From 53a3d24b95c33952dfeef7668c688fa717aa1fb1 Mon Sep 17 00:00:00 2001
From: Jake Bailey <5341706+jakebailey@users.noreply.github.com>
Date: Fri, 6 Oct 2023 16:23:54 -0700
Subject: [PATCH 1/7] Fix fallthrough and default in new switch-true narrowing
 (#55991)

---
 src/compiler/checker.ts                       |  36 +-
 ...rrowByClauseExpressionInSwitchTrue.symbols | 144 --------
 ...rowByClauseExpressionInSwitchTrue1.symbols | 144 ++++++++
 ...rrowByClauseExpressionInSwitchTrue1.types} |   4 +-
 ...owByClauseExpressionInSwitchTrue10.symbols | 107 ++++++
 ...rrowByClauseExpressionInSwitchTrue10.types | 111 ++++++
 ...rowByClauseExpressionInSwitchTrue2.symbols |  49 +++
 ...arrowByClauseExpressionInSwitchTrue2.types |  61 +++
 ...ByClauseExpressionInSwitchTrue3.errors.txt |  32 ++
 ...rowByClauseExpressionInSwitchTrue3.symbols |  60 +++
 ...arrowByClauseExpressionInSwitchTrue3.types |  77 ++++
 ...rowByClauseExpressionInSwitchTrue4.symbols |  21 ++
 ...arrowByClauseExpressionInSwitchTrue4.types |  27 ++
 ...rowByClauseExpressionInSwitchTrue5.symbols | 304 +++++++++++++++
 ...arrowByClauseExpressionInSwitchTrue5.types | 348 ++++++++++++++++++
 ...ByClauseExpressionInSwitchTrue6.errors.txt |  89 +++++
 ...rowByClauseExpressionInSwitchTrue6.symbols | 198 ++++++++++
 ...arrowByClauseExpressionInSwitchTrue6.types | 222 +++++++++++
 ...ByClauseExpressionInSwitchTrue7.errors.txt |  90 +++++
 ...rowByClauseExpressionInSwitchTrue7.symbols | 229 ++++++++++++
 ...arrowByClauseExpressionInSwitchTrue7.types | 253 +++++++++++++
 ...rowByClauseExpressionInSwitchTrue8.symbols |  57 +++
 ...arrowByClauseExpressionInSwitchTrue8.types |  59 +++
 ...rowByClauseExpressionInSwitchTrue9.symbols |  40 ++
 ...arrowByClauseExpressionInSwitchTrue9.types |  40 ++
 ... narrowByClauseExpressionInSwitchTrue1.ts} |   0
 .../narrowByClauseExpressionInSwitchTrue10.ts |  56 +++
 .../narrowByClauseExpressionInSwitchTrue2.ts  |  29 ++
 .../narrowByClauseExpressionInSwitchTrue3.ts  |  22 ++
 .../narrowByClauseExpressionInSwitchTrue4.ts  |  12 +
 .../narrowByClauseExpressionInSwitchTrue5.ts  | 133 +++++++
 .../narrowByClauseExpressionInSwitchTrue6.ts  |  78 ++++
 .../narrowByClauseExpressionInSwitchTrue7.ts  |  86 +++++
 .../narrowByClauseExpressionInSwitchTrue8.ts  |  32 ++
 .../narrowByClauseExpressionInSwitchTrue9.ts  |  20 +
 35 files changed, 3119 insertions(+), 151 deletions(-)
 delete mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue1.symbols
 rename tests/baselines/reference/{narrowByClauseExpressionInSwitchTrue.types => narrowByClauseExpressionInSwitchTrue1.types} (90%)
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue10.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue10.types
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue2.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue2.types
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.errors.txt
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.types
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue4.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue4.types
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue5.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue5.types
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.errors.txt
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.types
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.errors.txt
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.types
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue8.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue8.types
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue9.symbols
 create mode 100644 tests/baselines/reference/narrowByClauseExpressionInSwitchTrue9.types
 rename tests/cases/compiler/{narrowByClauseExpressionInSwitchTrue.ts => narrowByClauseExpressionInSwitchTrue1.ts} (100%)
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue10.ts
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue2.ts
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue3.ts
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue4.ts
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue5.ts
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue6.ts
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue7.ts
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue8.ts
 create mode 100644 tests/cases/compiler/narrowByClauseExpressionInSwitchTrue9.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 85700319fc371..2c9344679abd8 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -27456,11 +27456,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 type = narrowTypeBySwitchOnTypeOf(type, flow.switchStatement, flow.clauseStart, flow.clauseEnd);
             }
             else if (expr.kind === SyntaxKind.TrueKeyword) {
-                const clause = flow.switchStatement.caseBlock.clauses.find((_, index) => index === flow.clauseStart);
-                const clauseExpression = clause && clause.kind === SyntaxKind.CaseClause ? clause.expression : undefined;
-                if (clauseExpression) {
-                    type = narrowType(type, clauseExpression, /*assumeTrue*/ true);
-                }
+                type = narrowTypeBySwitchOnTrue(type, flow.switchStatement, flow.clauseStart, flow.clauseEnd);
             }
             else {
                 if (strictNullChecks) {
@@ -28075,6 +28071,36 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             return getUnionType(map(clauseWitnesses, text => text ? narrowTypeByTypeName(type, text) : neverType));
         }
 
+        function narrowTypeBySwitchOnTrue(type: Type, switchStatement: SwitchStatement, clauseStart: number, clauseEnd: number): Type {
+            const defaultIndex = findIndex(switchStatement.caseBlock.clauses, clause => clause.kind === SyntaxKind.DefaultClause);
+            const hasDefaultClause = clauseStart === clauseEnd || (defaultIndex >= clauseStart && defaultIndex < clauseEnd);
+
+            // First, narrow away all of the cases that preceded this set of cases.
+            for (let i = 0; i < clauseStart; i++) {
+                const clause = switchStatement.caseBlock.clauses[i];
+                if (clause.kind === SyntaxKind.CaseClause) {
+                    type = narrowType(type, clause.expression, /*assumeTrue*/ false);
+                }
+            }
+
+            // If our current set has a default, then none the other cases were hit either.
+            // There's no point in narrowing by the the other cases in the set, since we can
+            // get here through other paths.
+            if (hasDefaultClause) {
+                for (let i = clauseEnd; i < switchStatement.caseBlock.clauses.length; i++) {
+                    const clause = switchStatement.caseBlock.clauses[i];
+                    if (clause.kind === SyntaxKind.CaseClause) {
+                        type = narrowType(type, clause.expression, /*assumeTrue*/ false);
+                    }
+                }
+                return type;
+            }
+
+            // Now, narrow based on the cases in this set.
+            const clauses = switchStatement.caseBlock.clauses.slice(clauseStart, clauseEnd);
+            return getUnionType(map(clauses, clause => clause.kind === SyntaxKind.CaseClause ? narrowType(type, clause.expression, /*assumeTrue*/ true) : neverType));
+        }
+
         function isMatchingConstructorReference(expr: Expression) {
             return (isPropertyAccessExpression(expr) && idText(expr.name) === "constructor" ||
                 isElementAccessExpression(expr) && isStringLiteralLike(expr.argumentExpression) && expr.argumentExpression.text === "constructor") &&
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue.symbols
deleted file mode 100644
index 6461b7c88b263..0000000000000
--- a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue.symbols
+++ /dev/null
@@ -1,144 +0,0 @@
-//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue.ts] ////
-
-=== narrowByClauseExpressionInSwitchTrue.ts ===
-// https://github.com/microsoft/TypeScript/issues/37178
-
-type A = { type: "A" };
->A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue.ts, 0, 0))
->type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue.ts, 2, 10))
-
-type B = { type: "B" };
->B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue.ts, 2, 23))
->type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 10))
-
-type AorB = A | B;
->AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 23))
->A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue.ts, 0, 0))
->B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue.ts, 2, 23))
-
-const isA = (x: AorB): x is A => x.type === "A";
->isA : Symbol(isA, Decl(narrowByClauseExpressionInSwitchTrue.ts, 6, 5))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 6, 13))
->AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 23))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 6, 13))
->A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue.ts, 0, 0))
->x.type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 10))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 6, 13))
->type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 10))
-
-const isB = (x: AorB): x is B => x.type === "B";
->isB : Symbol(isB, Decl(narrowByClauseExpressionInSwitchTrue.ts, 7, 5))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 7, 13))
->AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 23))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 7, 13))
->B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue.ts, 2, 23))
->x.type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 10))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 7, 13))
->type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 10))
-
-function test1(x: AorB) {
->test1 : Symbol(test1, Decl(narrowByClauseExpressionInSwitchTrue.ts, 7, 48))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 9, 15))
->AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 23))
-
-  switch (true) {
-    case isA(x):
->isA : Symbol(isA, Decl(narrowByClauseExpressionInSwitchTrue.ts, 6, 5))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 9, 15))
-
-      x;
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 9, 15))
-
-      break;
-    case isB(x):
->isB : Symbol(isB, Decl(narrowByClauseExpressionInSwitchTrue.ts, 7, 5))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 9, 15))
-
-      x;
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 9, 15))
-
-      break;
-  }
-}
-
-function test2(x: AorB) {
->test2 : Symbol(test2, Decl(narrowByClauseExpressionInSwitchTrue.ts, 18, 1))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 20, 15))
->AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue.ts, 3, 23))
-
-  switch (true) {
-    case isA(x):
->isA : Symbol(isA, Decl(narrowByClauseExpressionInSwitchTrue.ts, 6, 5))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 20, 15))
-
-      x;
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 20, 15))
-
-    // fallthrough
-    case isB(x):
->isB : Symbol(isB, Decl(narrowByClauseExpressionInSwitchTrue.ts, 7, 5))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 20, 15))
-
-      x;
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 20, 15))
-
-      break;
-  }
-}
-
-let x: string | undefined;
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 31, 3))
-
-switch (true) {
-  case typeof x !== "undefined":
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 31, 3))
-
-    x.trim();
->x.trim : Symbol(String.trim, Decl(lib.es5.d.ts, --, --))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 31, 3))
->trim : Symbol(String.trim, Decl(lib.es5.d.ts, --, --))
-}
-
-type SomeType = { type: "SomeType" };
->SomeType : Symbol(SomeType, Decl(narrowByClauseExpressionInSwitchTrue.ts, 36, 1))
->type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue.ts, 38, 17))
-
-declare function isSomeType(x: unknown): x is SomeType;
->isSomeType : Symbol(isSomeType, Decl(narrowByClauseExpressionInSwitchTrue.ts, 38, 37))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 39, 28))
->x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue.ts, 39, 28))
->SomeType : Symbol(SomeType, Decl(narrowByClauseExpressionInSwitchTrue.ts, 36, 1))
-
-function processInput(input: string | RegExp | SomeType) {
->processInput : Symbol(processInput, Decl(narrowByClauseExpressionInSwitchTrue.ts, 39, 55))
->input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue.ts, 41, 22))
->RegExp : Symbol(RegExp, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
->SomeType : Symbol(SomeType, Decl(narrowByClauseExpressionInSwitchTrue.ts, 36, 1))
-
-  switch (true) {
-    case typeof input === "string":
->input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue.ts, 41, 22))
-
-      input;
->input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue.ts, 41, 22))
-
-      break;
-    case input instanceof RegExp:
->input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue.ts, 41, 22))
->RegExp : Symbol(RegExp, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
-
-      input;
->input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue.ts, 41, 22))
-
-      break;
-    case isSomeType(input):
->isSomeType : Symbol(isSomeType, Decl(narrowByClauseExpressionInSwitchTrue.ts, 38, 37))
->input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue.ts, 41, 22))
-
-      input;
->input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue.ts, 41, 22))
-
-      break;
-  }
-}
-
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue1.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue1.symbols
new file mode 100644
index 0000000000000..3892a6c7fddf4
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue1.symbols
@@ -0,0 +1,144 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue1.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue1.ts ===
+// https://github.com/microsoft/TypeScript/issues/37178
+
+type A = { type: "A" };
+>A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 0, 0))
+>type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 2, 10))
+
+type B = { type: "B" };
+>B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 2, 23))
+>type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 10))
+
+type AorB = A | B;
+>AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 23))
+>A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 0, 0))
+>B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 2, 23))
+
+const isA = (x: AorB): x is A => x.type === "A";
+>isA : Symbol(isA, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 6, 5))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 6, 13))
+>AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 23))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 6, 13))
+>A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 0, 0))
+>x.type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 10))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 6, 13))
+>type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 10))
+
+const isB = (x: AorB): x is B => x.type === "B";
+>isB : Symbol(isB, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 7, 5))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 7, 13))
+>AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 23))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 7, 13))
+>B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 2, 23))
+>x.type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 10))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 7, 13))
+>type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 10))
+
+function test1(x: AorB) {
+>test1 : Symbol(test1, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 7, 48))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 9, 15))
+>AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 23))
+
+  switch (true) {
+    case isA(x):
+>isA : Symbol(isA, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 6, 5))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 9, 15))
+
+      x;
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 9, 15))
+
+      break;
+    case isB(x):
+>isB : Symbol(isB, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 7, 5))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 9, 15))
+
+      x;
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 9, 15))
+
+      break;
+  }
+}
+
+function test2(x: AorB) {
+>test2 : Symbol(test2, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 18, 1))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 20, 15))
+>AorB : Symbol(AorB, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 3, 23))
+
+  switch (true) {
+    case isA(x):
+>isA : Symbol(isA, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 6, 5))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 20, 15))
+
+      x;
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 20, 15))
+
+    // fallthrough
+    case isB(x):
+>isB : Symbol(isB, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 7, 5))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 20, 15))
+
+      x;
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 20, 15))
+
+      break;
+  }
+}
+
+let x: string | undefined;
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 31, 3))
+
+switch (true) {
+  case typeof x !== "undefined":
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 31, 3))
+
+    x.trim();
+>x.trim : Symbol(String.trim, Decl(lib.es5.d.ts, --, --))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 31, 3))
+>trim : Symbol(String.trim, Decl(lib.es5.d.ts, --, --))
+}
+
+type SomeType = { type: "SomeType" };
+>SomeType : Symbol(SomeType, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 36, 1))
+>type : Symbol(type, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 38, 17))
+
+declare function isSomeType(x: unknown): x is SomeType;
+>isSomeType : Symbol(isSomeType, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 38, 37))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 39, 28))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 39, 28))
+>SomeType : Symbol(SomeType, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 36, 1))
+
+function processInput(input: string | RegExp | SomeType) {
+>processInput : Symbol(processInput, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 39, 55))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 41, 22))
+>RegExp : Symbol(RegExp, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>SomeType : Symbol(SomeType, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 36, 1))
+
+  switch (true) {
+    case typeof input === "string":
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 41, 22))
+
+      input;
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 41, 22))
+
+      break;
+    case input instanceof RegExp:
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 41, 22))
+>RegExp : Symbol(RegExp, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+
+      input;
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 41, 22))
+
+      break;
+    case isSomeType(input):
+>isSomeType : Symbol(isSomeType, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 38, 37))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 41, 22))
+
+      input;
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue1.ts, 41, 22))
+
+      break;
+  }
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue1.types
similarity index 90%
rename from tests/baselines/reference/narrowByClauseExpressionInSwitchTrue.types
rename to tests/baselines/reference/narrowByClauseExpressionInSwitchTrue1.types
index f8a1d9bc87e42..fa20aae9246ba 100644
--- a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue.types
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue1.types
@@ -1,6 +1,6 @@
-//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue.ts] ////
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue1.ts] ////
 
-=== narrowByClauseExpressionInSwitchTrue.ts ===
+=== narrowByClauseExpressionInSwitchTrue1.ts ===
 // https://github.com/microsoft/TypeScript/issues/37178
 
 type A = { type: "A" };
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue10.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue10.symbols
new file mode 100644
index 0000000000000..2abb5fc5d41ec
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue10.symbols
@@ -0,0 +1,107 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue10.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue10.ts ===
+function foo(cond1: boolean, cond2: boolean) {
+>foo : Symbol(foo, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 0))
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 13))
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 28))
+
+    switch (true) {
+        case cond1 || cond2:
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 13))
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 28))
+
+            cond1; // boolean
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 13))
+
+            //  ^?
+            cond2; // boolean
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 28))
+
+            //  ^?
+            break;
+
+        case cond2:
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 28))
+
+            cond1; // false
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 13))
+
+            //  ^?
+            cond2;; // never
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 28))
+
+            //  ^?
+            break;
+
+        default:
+            cond1; // false
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 13))
+
+            //  ^?
+            cond2; // false
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 28))
+
+            //  ^?
+            break;
+    }
+
+    cond1; // boolean
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 13))
+
+    //  ^?
+    cond2; // boolean
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 0, 28))
+
+    //  ^?
+}
+
+function blah(cond1: boolean, cond2: boolean) {
+>blah : Symbol(blah, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 28, 1))
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 14))
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 29))
+
+    if (cond1 || cond2) {
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 14))
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 29))
+
+        cond1; // boolean
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 14))
+
+        //  ^?
+        cond2; // boolean
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 29))
+
+        //  ^?
+    } else if (cond2) {
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 29))
+
+        cond1; // false
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 14))
+
+        //  ^?
+        cond2; // never
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 29))
+
+        //  ^?
+    } else {
+        cond1; // false
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 14))
+
+        //  ^?
+        cond2; // false
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 29))
+
+        //  ^?
+    }
+
+    cond1; // boolean
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 14))
+
+    //  ^?
+    cond2; // boolean
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue10.ts, 30, 29))
+
+    //  ^?
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue10.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue10.types
new file mode 100644
index 0000000000000..d6e8cedfdc64e
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue10.types
@@ -0,0 +1,111 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue10.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue10.ts ===
+function foo(cond1: boolean, cond2: boolean) {
+>foo : (cond1: boolean, cond2: boolean) => void
+>cond1 : boolean
+>cond2 : boolean
+
+    switch (true) {
+>true : true
+
+        case cond1 || cond2:
+>cond1 || cond2 : boolean
+>cond1 : boolean
+>cond2 : boolean
+
+            cond1; // boolean
+>cond1 : boolean
+
+            //  ^?
+            cond2; // boolean
+>cond2 : boolean
+
+            //  ^?
+            break;
+
+        case cond2:
+>cond2 : boolean
+
+            cond1; // false
+>cond1 : false
+
+            //  ^?
+            cond2;; // never
+>cond2 : never
+
+            //  ^?
+            break;
+
+        default:
+            cond1; // false
+>cond1 : false
+
+            //  ^?
+            cond2; // false
+>cond2 : false
+
+            //  ^?
+            break;
+    }
+
+    cond1; // boolean
+>cond1 : boolean
+
+    //  ^?
+    cond2; // boolean
+>cond2 : boolean
+
+    //  ^?
+}
+
+function blah(cond1: boolean, cond2: boolean) {
+>blah : (cond1: boolean, cond2: boolean) => void
+>cond1 : boolean
+>cond2 : boolean
+
+    if (cond1 || cond2) {
+>cond1 || cond2 : boolean
+>cond1 : boolean
+>cond2 : boolean
+
+        cond1; // boolean
+>cond1 : boolean
+
+        //  ^?
+        cond2; // boolean
+>cond2 : boolean
+
+        //  ^?
+    } else if (cond2) {
+>cond2 : false
+
+        cond1; // false
+>cond1 : false
+
+        //  ^?
+        cond2; // never
+>cond2 : never
+
+        //  ^?
+    } else {
+        cond1; // false
+>cond1 : false
+
+        //  ^?
+        cond2; // false
+>cond2 : false
+
+        //  ^?
+    }
+
+    cond1; // boolean
+>cond1 : boolean
+
+    //  ^?
+    cond2; // boolean
+>cond2 : boolean
+
+    //  ^?
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue2.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue2.symbols
new file mode 100644
index 0000000000000..8ce5e2928f487
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue2.symbols
@@ -0,0 +1,49 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue2.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue2.ts ===
+// https://github.com/microsoft/TypeScript/issues/55986
+
+declare const f: 'a' | 'b' | 'c';
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+switch(true) {
+    case f === 'a':
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+    case f === 'b':
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+        f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+        break
+    default:
+        f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+}
+
+f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+switch(true) {
+    case f === 'a':
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+        f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+    case f === 'b':
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+        f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
+        break
+    default:
+        f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+}
+
+f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue2.ts, 2, 13))
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue2.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue2.types
new file mode 100644
index 0000000000000..d1637eb248fd5
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue2.types
@@ -0,0 +1,61 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue2.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue2.ts ===
+// https://github.com/microsoft/TypeScript/issues/55986
+
+declare const f: 'a' | 'b' | 'c';
+>f : "a" | "b" | "c"
+
+switch(true) {
+>true : true
+
+    case f === 'a':
+>f === 'a' : boolean
+>f : "a" | "b" | "c"
+>'a' : "a"
+
+    case f === 'b':
+>f === 'b' : boolean
+>f : "a" | "b" | "c"
+>'b' : "b"
+
+        f;
+>f : "a" | "b"
+
+        break
+    default:
+        f;
+>f : "c"
+}
+
+f;
+>f : "a" | "b" | "c"
+
+switch(true) {
+>true : true
+
+    case f === 'a':
+>f === 'a' : boolean
+>f : "a" | "b" | "c"
+>'a' : "a"
+
+        f;
+>f : "a"
+
+    case f === 'b':
+>f === 'b' : boolean
+>f : "a" | "b" | "c"
+>'b' : "b"
+
+        f;
+>f : "a" | "b"
+
+        break
+    default:
+        f;
+>f : "c"
+}
+
+f;
+>f : "a" | "b" | "c"
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.errors.txt b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.errors.txt
new file mode 100644
index 0000000000000..cec1802a21fcf
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.errors.txt
@@ -0,0 +1,32 @@
+narrowByClauseExpressionInSwitchTrue3.ts(12,9): error TS2367: This comparison appears to be unintentional because the types '"square"' and '"circle"' have no overlap.
+narrowByClauseExpressionInSwitchTrue3.ts(13,32): error TS2339: Property 'radius' does not exist on type 'never'.
+narrowByClauseExpressionInSwitchTrue3.ts(15,14): error TS2367: This comparison appears to be unintentional because the types '"square"' and '"circle"' have no overlap.
+
+
+==== narrowByClauseExpressionInSwitchTrue3.ts (3 errors) ====
+    type Shape =
+        | { kind: "circle", radius: number }
+        | { kind: "square", sideLength: number }
+    
+    function wat(shape: Shape) {
+        switch (true) {
+            case shape.kind === "circle":
+                return Math.PI * shape.radius ** 2;
+            case shape.kind === "circle": // should error
+        }
+    
+        if (shape.kind === "circle") {
+            ~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2367: This comparison appears to be unintentional because the types '"square"' and '"circle"' have no overlap.
+            return Math.PI * shape.radius ** 2;
+                                   ~~~~~~
+!!! error TS2339: Property 'radius' does not exist on type 'never'.
+        }
+        else if (shape.kind === "circle") {
+                 ~~~~~~~~~~~~~~~~~~~~~~~
+!!! error TS2367: This comparison appears to be unintentional because the types '"square"' and '"circle"' have no overlap.
+            //         ~~~~
+            // Property 'kind' does not exist on type 'never'.
+        }
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.symbols
new file mode 100644
index 0000000000000..b6811492524e1
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.symbols
@@ -0,0 +1,60 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue3.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue3.ts ===
+type Shape =
+>Shape : Symbol(Shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 0, 0))
+
+    | { kind: "circle", radius: number }
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 1, 7))
+>radius : Symbol(radius, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 1, 23))
+
+    | { kind: "square", sideLength: number }
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+>sideLength : Symbol(sideLength, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 23))
+
+function wat(shape: Shape) {
+>wat : Symbol(wat, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 44))
+>shape : Symbol(shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 4, 13))
+>Shape : Symbol(Shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 0, 0))
+
+    switch (true) {
+        case shape.kind === "circle":
+>shape.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 1, 7), Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+>shape : Symbol(shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 4, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 1, 7), Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+
+            return Math.PI * shape.radius ** 2;
+>Math.PI : Symbol(Math.PI, Decl(lib.es5.d.ts, --, --))
+>Math : Symbol(Math, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>PI : Symbol(Math.PI, Decl(lib.es5.d.ts, --, --))
+>shape.radius : Symbol(radius, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 1, 23))
+>shape : Symbol(shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 4, 13))
+>radius : Symbol(radius, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 1, 23))
+
+        case shape.kind === "circle": // should error
+>shape.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 1, 7), Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+>shape : Symbol(shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 4, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 1, 7), Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+    }
+
+    if (shape.kind === "circle") {
+>shape.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+>shape : Symbol(shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 4, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+
+        return Math.PI * shape.radius ** 2;
+>Math.PI : Symbol(Math.PI, Decl(lib.es5.d.ts, --, --))
+>Math : Symbol(Math, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>PI : Symbol(Math.PI, Decl(lib.es5.d.ts, --, --))
+>shape : Symbol(shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 4, 13))
+    }
+    else if (shape.kind === "circle") {
+>shape.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+>shape : Symbol(shape, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 4, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue3.ts, 2, 7))
+
+        //         ~~~~
+        // Property 'kind' does not exist on type 'never'.
+    }
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.types
new file mode 100644
index 0000000000000..1fde85a02984d
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue3.types
@@ -0,0 +1,77 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue3.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue3.ts ===
+type Shape =
+>Shape : { kind: "circle"; radius: number; } | { kind: "square"; sideLength: number; }
+
+    | { kind: "circle", radius: number }
+>kind : "circle"
+>radius : number
+
+    | { kind: "square", sideLength: number }
+>kind : "square"
+>sideLength : number
+
+function wat(shape: Shape) {
+>wat : (shape: Shape) => number | undefined
+>shape : Shape
+
+    switch (true) {
+>true : true
+
+        case shape.kind === "circle":
+>shape.kind === "circle" : boolean
+>shape.kind : "circle" | "square"
+>shape : Shape
+>kind : "circle" | "square"
+>"circle" : "circle"
+
+            return Math.PI * shape.radius ** 2;
+>Math.PI * shape.radius ** 2 : number
+>Math.PI : number
+>Math : Math
+>PI : number
+>shape.radius ** 2 : number
+>shape.radius : number
+>shape : { kind: "circle"; radius: number; }
+>radius : number
+>2 : 2
+
+        case shape.kind === "circle": // should error
+>shape.kind === "circle" : boolean
+>shape.kind : "circle" | "square"
+>shape : Shape
+>kind : "circle" | "square"
+>"circle" : "circle"
+    }
+
+    if (shape.kind === "circle") {
+>shape.kind === "circle" : boolean
+>shape.kind : "square"
+>shape : { kind: "square"; sideLength: number; }
+>kind : "square"
+>"circle" : "circle"
+
+        return Math.PI * shape.radius ** 2;
+>Math.PI * shape.radius ** 2 : number
+>Math.PI : number
+>Math : Math
+>PI : number
+>shape.radius ** 2 : number
+>shape.radius : any
+>shape : never
+>radius : any
+>2 : 2
+    }
+    else if (shape.kind === "circle") {
+>shape.kind === "circle" : boolean
+>shape.kind : "square"
+>shape : { kind: "square"; sideLength: number; }
+>kind : "square"
+>"circle" : "circle"
+
+        //         ~~~~
+        // Property 'kind' does not exist on type 'never'.
+    }
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue4.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue4.symbols
new file mode 100644
index 0000000000000..c505b1d47c975
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue4.symbols
@@ -0,0 +1,21 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue4.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue4.ts ===
+declare const f: 'a' | 'b' | 'c';
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue4.ts, 0, 13))
+
+switch (true) {
+  case f === "a":
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue4.ts, 0, 13))
+
+  default:
+    f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue4.ts, 0, 13))
+
+  case f === "b":
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue4.ts, 0, 13))
+
+    f;
+>f : Symbol(f, Decl(narrowByClauseExpressionInSwitchTrue4.ts, 0, 13))
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue4.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue4.types
new file mode 100644
index 0000000000000..8dc6062a2b695
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue4.types
@@ -0,0 +1,27 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue4.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue4.ts ===
+declare const f: 'a' | 'b' | 'c';
+>f : "a" | "b" | "c"
+
+switch (true) {
+>true : true
+
+  case f === "a":
+>f === "a" : boolean
+>f : "a" | "b" | "c"
+>"a" : "a"
+
+  default:
+    f;
+>f : "a" | "c"
+
+  case f === "b":
+>f === "b" : boolean
+>f : "a" | "b" | "c"
+>"b" : "b"
+
+    f;
+>f : "a" | "b" | "c"
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue5.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue5.symbols
new file mode 100644
index 0000000000000..3c890662516f5
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue5.symbols
@@ -0,0 +1,304 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue5.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue5.ts ===
+type A = { kind: "A", value: number };
+>A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 0))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10))
+>value : Symbol(value, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 21))
+
+type B = { kind: "B", name: string };
+>B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 38))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+>name : Symbol(name, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 21))
+
+type C = { kind: "C", cond: boolean };
+>C : Symbol(C, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 37))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10))
+>cond : Symbol(cond, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 21))
+
+type D = { kind: "D", value: boolean };
+>D : Symbol(D, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 38))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10))
+>value : Symbol(value, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 21))
+
+type E = { kind: "E", x: number, y: number };
+>E : Symbol(E, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 39))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 21))
+>y : Symbol(y, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 32))
+
+type All = A | B | C | D | E;
+>All : Symbol(All, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 45))
+>A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 0))
+>B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 38))
+>C : Symbol(C, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 37))
+>D : Symbol(D, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 38))
+>E : Symbol(E, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 39))
+
+function fn1switch(input: All) {
+>fn1switch : Symbol(fn1switch, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 6, 29))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+>All : Symbol(All, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 45))
+
+    switch (true) {
+        case input.kind === "A":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+        case input.kind === "B":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+            if (input.kind === "A") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+
+                return;
+            }
+
+            input; // Should be B;
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+
+            //  ^?
+
+            // fallthrough
+        case input.kind === "C":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+            input; // Should be B | C
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+
+            //  ^?
+            break;
+        default:
+            input; // Should be D | E
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+
+            //  ^?
+    }
+
+    input; // Should not be A
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 8, 19))
+
+    //  ^?
+}
+
+function fn1ifelse(input: All) {
+>fn1ifelse : Symbol(fn1ifelse, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 31, 1))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+>All : Symbol(All, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 45))
+
+    if (input.kind === "A" || input.kind === "B") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+        if (input.kind === "A") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+
+            return;
+        }
+
+        input; // Should be B;
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+
+        //  ^?
+    }
+    if (input.kind === "C" || input.kind === "B") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+        input; // Should be B | C
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+
+        //  ^?
+    }
+    else {
+        input; // Should be D | E
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+
+        //  ^?
+    }
+
+    input; // Should not be A
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 33, 19))
+
+    //  ^?
+}
+
+function fn2switch(input: All) {
+>fn2switch : Symbol(fn2switch, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 53, 1))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+>All : Symbol(All, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 45))
+
+    switch (true) {
+        case input.kind === "A":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+        case input.kind === "B":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+            if (input.kind === "A") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+
+                return;
+            }
+
+            input; // Should be B;
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+
+            //  ^?
+
+            // fallthrough
+        case input.kind === "C":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+            input; // Should be B | C
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+
+            //  ^?
+            break;
+        default:
+            input; // Should be D | E
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+
+            //  ^?
+            return;
+    }
+
+    input; // Should be B | C
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 55, 19))
+
+    //  ^?
+}
+
+function fn2ifelse(input: All) {
+>fn2ifelse : Symbol(fn2ifelse, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 79, 1))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+>All : Symbol(All, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 45))
+
+    if (input.kind === "A" || input.kind === "B") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+        if (input.kind === "A") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+
+            return;
+        }
+
+        input; // Should be B;
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+
+        //  ^?
+    }
+    if (input.kind === "C" || input.kind === "B") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+        input; // Should be B | C
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+
+        //  ^?
+    }
+    else {
+        input; // Should be D | E
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+
+        //  ^?
+        return;
+    }
+
+    input; // Should be B | C
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 81, 19))
+
+    //  ^?
+}
+
+function fn3switch(input: All) {
+>fn3switch : Symbol(fn3switch, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 102, 1))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+>All : Symbol(All, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 45))
+
+    switch (true) {
+        case input.kind === "A":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+        case input.kind === "B":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+            if (input.kind === "A") {
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10))
+
+                return;
+            }
+
+            input; // Should be B;
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+
+            //  ^?
+
+            // fallthrough
+        default:
+            input; // Should be B | D | E
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+
+            //  ^?
+            break;
+
+        case input.kind === "C":
+>input.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 0, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 1, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 2, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 3, 10), Decl(narrowByClauseExpressionInSwitchTrue5.ts, 4, 10))
+
+            input; // Should be C
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+
+            //  ^?
+            break;
+    }
+
+    input; // Should not be A
+>input : Symbol(input, Decl(narrowByClauseExpressionInSwitchTrue5.ts, 104, 19))
+
+    //  ^?
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue5.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue5.types
new file mode 100644
index 0000000000000..d2b4c5c0780de
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue5.types
@@ -0,0 +1,348 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue5.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue5.ts ===
+type A = { kind: "A", value: number };
+>A : { kind: "A"; value: number; }
+>kind : "A"
+>value : number
+
+type B = { kind: "B", name: string };
+>B : { kind: "B"; name: string; }
+>kind : "B"
+>name : string
+
+type C = { kind: "C", cond: boolean };
+>C : { kind: "C"; cond: boolean; }
+>kind : "C"
+>cond : boolean
+
+type D = { kind: "D", value: boolean };
+>D : { kind: "D"; value: boolean; }
+>kind : "D"
+>value : boolean
+
+type E = { kind: "E", x: number, y: number };
+>E : { kind: "E"; x: number; y: number; }
+>kind : "E"
+>x : number
+>y : number
+
+type All = A | B | C | D | E;
+>All : A | B | C | D | E
+
+function fn1switch(input: All) {
+>fn1switch : (input: All) => void
+>input : All
+
+    switch (true) {
+>true : true
+
+        case input.kind === "A":
+>input.kind === "A" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"A" : "A"
+
+        case input.kind === "B":
+>input.kind === "B" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"B" : "B"
+
+            if (input.kind === "A") {
+>input.kind === "A" : boolean
+>input.kind : "A" | "B"
+>input : A | B
+>kind : "A" | "B"
+>"A" : "A"
+
+                return;
+            }
+
+            input; // Should be B;
+>input : B
+
+            //  ^?
+
+            // fallthrough
+        case input.kind === "C":
+>input.kind === "C" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"C" : "C"
+
+            input; // Should be B | C
+>input : B | C
+
+            //  ^?
+            break;
+        default:
+            input; // Should be D | E
+>input : D | E
+
+            //  ^?
+    }
+
+    input; // Should not be A
+>input : B | C | D | E
+
+    //  ^?
+}
+
+function fn1ifelse(input: All) {
+>fn1ifelse : (input: All) => void
+>input : All
+
+    if (input.kind === "A" || input.kind === "B") {
+>input.kind === "A" || input.kind === "B" : boolean
+>input.kind === "A" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"A" : "A"
+>input.kind === "B" : boolean
+>input.kind : "B" | "C" | "D" | "E"
+>input : B | C | D | E
+>kind : "B" | "C" | "D" | "E"
+>"B" : "B"
+
+        if (input.kind === "A") {
+>input.kind === "A" : boolean
+>input.kind : "A" | "B"
+>input : A | B
+>kind : "A" | "B"
+>"A" : "A"
+
+            return;
+        }
+
+        input; // Should be B;
+>input : B
+
+        //  ^?
+    }
+    if (input.kind === "C" || input.kind === "B") {
+>input.kind === "C" || input.kind === "B" : boolean
+>input.kind === "C" : boolean
+>input.kind : "B" | "C" | "D" | "E"
+>input : B | C | D | E
+>kind : "B" | "C" | "D" | "E"
+>"C" : "C"
+>input.kind === "B" : boolean
+>input.kind : "B" | "D" | "E"
+>input : B | D | E
+>kind : "B" | "D" | "E"
+>"B" : "B"
+
+        input; // Should be B | C
+>input : B | C
+
+        //  ^?
+    }
+    else {
+        input; // Should be D | E
+>input : D | E
+
+        //  ^?
+    }
+
+    input; // Should not be A
+>input : B | C | D | E
+
+    //  ^?
+}
+
+function fn2switch(input: All) {
+>fn2switch : (input: All) => void
+>input : All
+
+    switch (true) {
+>true : true
+
+        case input.kind === "A":
+>input.kind === "A" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"A" : "A"
+
+        case input.kind === "B":
+>input.kind === "B" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"B" : "B"
+
+            if (input.kind === "A") {
+>input.kind === "A" : boolean
+>input.kind : "A" | "B"
+>input : A | B
+>kind : "A" | "B"
+>"A" : "A"
+
+                return;
+            }
+
+            input; // Should be B;
+>input : B
+
+            //  ^?
+
+            // fallthrough
+        case input.kind === "C":
+>input.kind === "C" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"C" : "C"
+
+            input; // Should be B | C
+>input : B | C
+
+            //  ^?
+            break;
+        default:
+            input; // Should be D | E
+>input : D | E
+
+            //  ^?
+            return;
+    }
+
+    input; // Should be B | C
+>input : B | C
+
+    //  ^?
+}
+
+function fn2ifelse(input: All) {
+>fn2ifelse : (input: All) => void
+>input : All
+
+    if (input.kind === "A" || input.kind === "B") {
+>input.kind === "A" || input.kind === "B" : boolean
+>input.kind === "A" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"A" : "A"
+>input.kind === "B" : boolean
+>input.kind : "B" | "C" | "D" | "E"
+>input : B | C | D | E
+>kind : "B" | "C" | "D" | "E"
+>"B" : "B"
+
+        if (input.kind === "A") {
+>input.kind === "A" : boolean
+>input.kind : "A" | "B"
+>input : A | B
+>kind : "A" | "B"
+>"A" : "A"
+
+            return;
+        }
+
+        input; // Should be B;
+>input : B
+
+        //  ^?
+    }
+    if (input.kind === "C" || input.kind === "B") {
+>input.kind === "C" || input.kind === "B" : boolean
+>input.kind === "C" : boolean
+>input.kind : "B" | "C" | "D" | "E"
+>input : B | C | D | E
+>kind : "B" | "C" | "D" | "E"
+>"C" : "C"
+>input.kind === "B" : boolean
+>input.kind : "B" | "D" | "E"
+>input : B | D | E
+>kind : "B" | "D" | "E"
+>"B" : "B"
+
+        input; // Should be B | C
+>input : B | C
+
+        //  ^?
+    }
+    else {
+        input; // Should be D | E
+>input : D | E
+
+        //  ^?
+        return;
+    }
+
+    input; // Should be B | C
+>input : B | C
+
+    //  ^?
+}
+
+function fn3switch(input: All) {
+>fn3switch : (input: All) => void
+>input : All
+
+    switch (true) {
+>true : true
+
+        case input.kind === "A":
+>input.kind === "A" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"A" : "A"
+
+        case input.kind === "B":
+>input.kind === "B" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"B" : "B"
+
+            if (input.kind === "A") {
+>input.kind === "A" : boolean
+>input.kind : "A" | "B"
+>input : A | B
+>kind : "A" | "B"
+>"A" : "A"
+
+                return;
+            }
+
+            input; // Should be B;
+>input : B
+
+            //  ^?
+
+            // fallthrough
+        default:
+            input; // Should be B | D | E
+>input : B | D | E
+
+            //  ^?
+            break;
+
+        case input.kind === "C":
+>input.kind === "C" : boolean
+>input.kind : "A" | "B" | "C" | "D" | "E"
+>input : All
+>kind : "A" | "B" | "C" | "D" | "E"
+>"C" : "C"
+
+            input; // Should be C
+>input : C
+
+            //  ^?
+            break;
+    }
+
+    input; // Should not be A
+>input : B | C | D | E
+
+    //  ^?
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.errors.txt b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.errors.txt
new file mode 100644
index 0000000000000..e33e6ac6fceab
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.errors.txt
@@ -0,0 +1,89 @@
+narrowByClauseExpressionInSwitchTrue6.ts(70,15): error TS2339: Property 'bProps' does not exist on type 'A | B'.
+  Property 'bProps' does not exist on type 'A'.
+narrowByClauseExpressionInSwitchTrue6.ts(73,15): error TS2339: Property 'cProps' does not exist on type 'MyType'.
+  Property 'cProps' does not exist on type 'A'.
+
+
+==== narrowByClauseExpressionInSwitchTrue6.ts (2 errors) ====
+    interface A {
+        kind: "a";
+        aProps: string;
+    }
+    
+    interface B {
+        kind: "b";
+        bProps: string;
+    }
+    
+    interface C {
+        kind: "c";
+        cProps: string;
+    }
+    
+    
+    type MyType = A | B | C;
+    
+    function isA(x: MyType) {
+        switch (true) {
+            default:
+                const never: never = x;
+            case x.kind === "a":
+                x.aProps;
+                break;
+            case x.kind === "b":
+                x.bProps;
+                break;
+            case x.kind === "c":
+                x.cProps;
+                break;
+        }
+    
+        switch (true) {
+            default:
+                const never: never = x;
+            case x.kind === "a": {
+                x.aProps;
+                break;
+            }
+            case x.kind === "b": {
+                x.bProps;
+                break;
+            }
+            case x.kind === "c": {
+                x.cProps;
+                break;
+            }
+        }
+        
+        switch (true) {
+            default:
+                x.aProps;
+                break;
+            case x.kind === "b":
+                x.bProps;
+                break;
+            case x.kind === "c":
+                x.cProps;
+                break;
+        }
+    
+        switch (true) {
+            default:
+                const never: never = x;
+            case x.kind === "a":
+                x.aProps;
+                // fallthrough
+            case x.kind === "b":
+                x.bProps;
+                  ~~~~~~
+!!! error TS2339: Property 'bProps' does not exist on type 'A | B'.
+!!! error TS2339:   Property 'bProps' does not exist on type 'A'.
+                // fallthrough
+            case x.kind === "c":
+                x.cProps;
+                  ~~~~~~
+!!! error TS2339: Property 'cProps' does not exist on type 'MyType'.
+!!! error TS2339:   Property 'cProps' does not exist on type 'A'.
+        }
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.symbols
new file mode 100644
index 0000000000000..9ed6be6a7cf6c
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.symbols
@@ -0,0 +1,198 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue6.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue6.ts ===
+interface A {
+>A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 0))
+
+    kind: "a";
+>kind : Symbol(A.kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13))
+
+    aProps: string;
+>aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+}
+
+interface B {
+>B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 3, 1))
+
+    kind: "b";
+>kind : Symbol(B.kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13))
+
+    bProps: string;
+>bProps : Symbol(B.bProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 6, 14))
+}
+
+interface C {
+>C : Symbol(C, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 8, 1))
+
+    kind: "c";
+>kind : Symbol(C.kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+    cProps: string;
+>cProps : Symbol(C.cProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 11, 14))
+}
+
+
+type MyType = A | B | C;
+>MyType : Symbol(MyType, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 13, 1))
+>A : Symbol(A, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 0))
+>B : Symbol(B, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 3, 1))
+>C : Symbol(C, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 8, 1))
+
+function isA(x: MyType) {
+>isA : Symbol(isA, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 16, 24))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>MyType : Symbol(MyType, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 13, 1))
+
+    switch (true) {
+        default:
+            const never: never = x;
+>never : Symbol(never, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 21, 17))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+
+        case x.kind === "a":
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.aProps;
+>x.aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+
+            break;
+        case x.kind === "b":
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.bProps;
+>x.bProps : Symbol(B.bProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 6, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>bProps : Symbol(B.bProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 6, 14))
+
+            break;
+        case x.kind === "c":
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.cProps;
+>x.cProps : Symbol(C.cProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 11, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>cProps : Symbol(C.cProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 11, 14))
+
+            break;
+    }
+
+    switch (true) {
+        default:
+            const never: never = x;
+>never : Symbol(never, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 35, 17))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+
+        case x.kind === "a": {
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.aProps;
+>x.aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+
+            break;
+        }
+        case x.kind === "b": {
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.bProps;
+>x.bProps : Symbol(B.bProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 6, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>bProps : Symbol(B.bProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 6, 14))
+
+            break;
+        }
+        case x.kind === "c": {
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.cProps;
+>x.cProps : Symbol(C.cProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 11, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>cProps : Symbol(C.cProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 11, 14))
+
+            break;
+        }
+    }
+    
+    switch (true) {
+        default:
+            x.aProps;
+>x.aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+
+            break;
+        case x.kind === "b":
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.bProps;
+>x.bProps : Symbol(B.bProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 6, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>bProps : Symbol(B.bProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 6, 14))
+
+            break;
+        case x.kind === "c":
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.cProps;
+>x.cProps : Symbol(C.cProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 11, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>cProps : Symbol(C.cProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 11, 14))
+
+            break;
+    }
+
+    switch (true) {
+        default:
+            const never: never = x;
+>never : Symbol(never, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 64, 17))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+
+        case x.kind === "a":
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.aProps;
+>x.aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>aProps : Symbol(A.aProps, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 1, 14))
+
+            // fallthrough
+        case x.kind === "b":
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.bProps;
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+
+            // fallthrough
+        case x.kind === "c":
+>x.kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+>kind : Symbol(kind, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 0, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 5, 13), Decl(narrowByClauseExpressionInSwitchTrue6.ts, 10, 13))
+
+            x.cProps;
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue6.ts, 18, 13))
+    }
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.types
new file mode 100644
index 0000000000000..4a96c67b07136
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue6.types
@@ -0,0 +1,222 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue6.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue6.ts ===
+interface A {
+    kind: "a";
+>kind : "a"
+
+    aProps: string;
+>aProps : string
+}
+
+interface B {
+    kind: "b";
+>kind : "b"
+
+    bProps: string;
+>bProps : string
+}
+
+interface C {
+    kind: "c";
+>kind : "c"
+
+    cProps: string;
+>cProps : string
+}
+
+
+type MyType = A | B | C;
+>MyType : A | B | C
+
+function isA(x: MyType) {
+>isA : (x: MyType) => void
+>x : MyType
+
+    switch (true) {
+>true : true
+
+        default:
+            const never: never = x;
+>never : never
+>x : never
+
+        case x.kind === "a":
+>x.kind === "a" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"a" : "a"
+
+            x.aProps;
+>x.aProps : string
+>x : A
+>aProps : string
+
+            break;
+        case x.kind === "b":
+>x.kind === "b" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"b" : "b"
+
+            x.bProps;
+>x.bProps : string
+>x : B
+>bProps : string
+
+            break;
+        case x.kind === "c":
+>x.kind === "c" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"c" : "c"
+
+            x.cProps;
+>x.cProps : string
+>x : C
+>cProps : string
+
+            break;
+    }
+
+    switch (true) {
+>true : true
+
+        default:
+            const never: never = x;
+>never : never
+>x : never
+
+        case x.kind === "a": {
+>x.kind === "a" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"a" : "a"
+
+            x.aProps;
+>x.aProps : string
+>x : A
+>aProps : string
+
+            break;
+        }
+        case x.kind === "b": {
+>x.kind === "b" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"b" : "b"
+
+            x.bProps;
+>x.bProps : string
+>x : B
+>bProps : string
+
+            break;
+        }
+        case x.kind === "c": {
+>x.kind === "c" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"c" : "c"
+
+            x.cProps;
+>x.cProps : string
+>x : C
+>cProps : string
+
+            break;
+        }
+    }
+    
+    switch (true) {
+>true : true
+
+        default:
+            x.aProps;
+>x.aProps : string
+>x : A
+>aProps : string
+
+            break;
+        case x.kind === "b":
+>x.kind === "b" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"b" : "b"
+
+            x.bProps;
+>x.bProps : string
+>x : B
+>bProps : string
+
+            break;
+        case x.kind === "c":
+>x.kind === "c" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"c" : "c"
+
+            x.cProps;
+>x.cProps : string
+>x : C
+>cProps : string
+
+            break;
+    }
+
+    switch (true) {
+>true : true
+
+        default:
+            const never: never = x;
+>never : never
+>x : never
+
+        case x.kind === "a":
+>x.kind === "a" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"a" : "a"
+
+            x.aProps;
+>x.aProps : string
+>x : A
+>aProps : string
+
+            // fallthrough
+        case x.kind === "b":
+>x.kind === "b" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"b" : "b"
+
+            x.bProps;
+>x.bProps : any
+>x : A | B
+>bProps : any
+
+            // fallthrough
+        case x.kind === "c":
+>x.kind === "c" : boolean
+>x.kind : "a" | "b" | "c"
+>x : MyType
+>kind : "a" | "b" | "c"
+>"c" : "c"
+
+            x.cProps;
+>x.cProps : any
+>x : MyType
+>cProps : any
+    }
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.errors.txt b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.errors.txt
new file mode 100644
index 0000000000000..ae09d39b7ca88
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.errors.txt
@@ -0,0 +1,90 @@
+narrowByClauseExpressionInSwitchTrue7.ts(80,19): error TS2322: Type 'Derived2' is not assignable to type 'never'.
+
+
+==== narrowByClauseExpressionInSwitchTrue7.ts (1 errors) ====
+    class Base {
+        basey: string = "";
+    }
+    
+    class Derived1 extends Base {
+        d: string = "";
+    }
+    
+    class Derived2 extends Base {
+        d: string = "";
+        other: string = "";
+    }
+    
+    function classy(base: Base, someDerived: Derived1 | Derived2) {
+        switch (true) {
+            case base instanceof Derived1:
+                base.d
+                // fallthrough
+            default:
+                base.basey
+        }
+    
+        switch (true) {
+            case someDerived instanceof Derived1:
+                someDerived.d
+                break;
+            case someDerived instanceof Derived2:
+                someDerived.d
+                break
+            default:
+                const never: never = someDerived;
+        }
+    
+        switch (true) {
+            case someDerived instanceof Derived1:
+                someDerived.d
+                // fallthrough
+            case someDerived instanceof Derived2:
+                someDerived.d
+                break
+            default:
+                const never: never = someDerived;
+        }
+    
+        switch (true) {
+            default:
+                const never: never = someDerived;
+            case someDerived instanceof Derived1:
+                someDerived.d;
+                someDerived.basey;
+                break
+            case someDerived instanceof Derived2:
+                someDerived.d;
+                someDerived.other;
+        }
+    
+        switch (true) {
+            case someDerived instanceof Derived1:
+                someDerived.d;
+                someDerived.basey;
+                break
+            default:
+                const never: never = someDerived;
+            case someDerived instanceof Derived2:
+                someDerived.d;
+                someDerived.other;
+        }
+    
+        switch (true) {
+            case someDerived instanceof Derived1:
+                someDerived.d;
+                someDerived.basey;
+                break
+            case someDerived instanceof Derived2:
+                someDerived.d;
+                someDerived.other;
+            default:
+                someDerived.d;
+                someDerived.other;
+                const never: never = someDerived;
+                      ~~~~~
+!!! error TS2322: Type 'Derived2' is not assignable to type 'never'.
+        }
+    
+    }
+    
\ No newline at end of file
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.symbols
new file mode 100644
index 0000000000000..ad0dd8f89d894
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.symbols
@@ -0,0 +1,229 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue7.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue7.ts ===
+class Base {
+>Base : Symbol(Base, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 0))
+
+    basey: string = "";
+>basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+}
+
+class Derived1 extends Base {
+>Derived1 : Symbol(Derived1, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 2, 1))
+>Base : Symbol(Base, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 0))
+
+    d: string = "";
+>d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+}
+
+class Derived2 extends Base {
+>Derived2 : Symbol(Derived2, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 6, 1))
+>Base : Symbol(Base, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 0))
+
+    d: string = "";
+>d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+
+    other: string = "";
+>other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+}
+
+function classy(base: Base, someDerived: Derived1 | Derived2) {
+>classy : Symbol(classy, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 11, 1))
+>base : Symbol(base, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 16))
+>Base : Symbol(Base, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 0))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived1 : Symbol(Derived1, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 2, 1))
+>Derived2 : Symbol(Derived2, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 6, 1))
+
+    switch (true) {
+        case base instanceof Derived1:
+>base : Symbol(base, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 16))
+>Derived1 : Symbol(Derived1, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 2, 1))
+
+            base.d
+>base.d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+>base : Symbol(base, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 16))
+>d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+
+            // fallthrough
+        default:
+            base.basey
+>base.basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+>base : Symbol(base, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 16))
+>basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+    }
+
+    switch (true) {
+        case someDerived instanceof Derived1:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived1 : Symbol(Derived1, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 2, 1))
+
+            someDerived.d
+>someDerived.d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+
+            break;
+        case someDerived instanceof Derived2:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived2 : Symbol(Derived2, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 6, 1))
+
+            someDerived.d
+>someDerived.d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+
+            break
+        default:
+            const never: never = someDerived;
+>never : Symbol(never, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 30, 17))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+    }
+
+    switch (true) {
+        case someDerived instanceof Derived1:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived1 : Symbol(Derived1, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 2, 1))
+
+            someDerived.d
+>someDerived.d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+
+            // fallthrough
+        case someDerived instanceof Derived2:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived2 : Symbol(Derived2, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 6, 1))
+
+            someDerived.d
+>someDerived.d : Symbol(d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29), Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29), Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+
+            break
+        default:
+            const never: never = someDerived;
+>never : Symbol(never, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 41, 17))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+    }
+
+    switch (true) {
+        default:
+            const never: never = someDerived;
+>never : Symbol(never, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 46, 17))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+
+        case someDerived instanceof Derived1:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived1 : Symbol(Derived1, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 2, 1))
+
+            someDerived.d;
+>someDerived.d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+
+            someDerived.basey;
+>someDerived.basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+
+            break
+        case someDerived instanceof Derived2:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived2 : Symbol(Derived2, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 6, 1))
+
+            someDerived.d;
+>someDerived.d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+
+            someDerived.other;
+>someDerived.other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+    }
+
+    switch (true) {
+        case someDerived instanceof Derived1:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived1 : Symbol(Derived1, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 2, 1))
+
+            someDerived.d;
+>someDerived.d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+
+            someDerived.basey;
+>someDerived.basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+
+            break
+        default:
+            const never: never = someDerived;
+>never : Symbol(never, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 62, 17))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+
+        case someDerived instanceof Derived2:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived2 : Symbol(Derived2, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 6, 1))
+
+            someDerived.d;
+>someDerived.d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+
+            someDerived.other;
+>someDerived.other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+    }
+
+    switch (true) {
+        case someDerived instanceof Derived1:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived1 : Symbol(Derived1, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 2, 1))
+
+            someDerived.d;
+>someDerived.d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived1.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 4, 29))
+
+            someDerived.basey;
+>someDerived.basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>basey : Symbol(Base.basey, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 0, 12))
+
+            break
+        case someDerived instanceof Derived2:
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>Derived2 : Symbol(Derived2, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 6, 1))
+
+            someDerived.d;
+>someDerived.d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+
+            someDerived.other;
+>someDerived.other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+
+        default:
+            someDerived.d;
+>someDerived.d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>d : Symbol(Derived2.d, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 8, 29))
+
+            someDerived.other;
+>someDerived.other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+>other : Symbol(Derived2.other, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 9, 19))
+
+            const never: never = someDerived;
+>never : Symbol(never, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 79, 17))
+>someDerived : Symbol(someDerived, Decl(narrowByClauseExpressionInSwitchTrue7.ts, 13, 27))
+    }
+
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.types
new file mode 100644
index 0000000000000..a783c583b22f3
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue7.types
@@ -0,0 +1,253 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue7.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue7.ts ===
+class Base {
+>Base : Base
+
+    basey: string = "";
+>basey : string
+>"" : ""
+}
+
+class Derived1 extends Base {
+>Derived1 : Derived1
+>Base : Base
+
+    d: string = "";
+>d : string
+>"" : ""
+}
+
+class Derived2 extends Base {
+>Derived2 : Derived2
+>Base : Base
+
+    d: string = "";
+>d : string
+>"" : ""
+
+    other: string = "";
+>other : string
+>"" : ""
+}
+
+function classy(base: Base, someDerived: Derived1 | Derived2) {
+>classy : (base: Base, someDerived: Derived1 | Derived2) => void
+>base : Base
+>someDerived : Derived1 | Derived2
+
+    switch (true) {
+>true : true
+
+        case base instanceof Derived1:
+>base instanceof Derived1 : boolean
+>base : Base
+>Derived1 : typeof Derived1
+
+            base.d
+>base.d : string
+>base : Derived1
+>d : string
+
+            // fallthrough
+        default:
+            base.basey
+>base.basey : string
+>base : Base
+>basey : string
+    }
+
+    switch (true) {
+>true : true
+
+        case someDerived instanceof Derived1:
+>someDerived instanceof Derived1 : boolean
+>someDerived : Derived1 | Derived2
+>Derived1 : typeof Derived1
+
+            someDerived.d
+>someDerived.d : string
+>someDerived : Derived1
+>d : string
+
+            break;
+        case someDerived instanceof Derived2:
+>someDerived instanceof Derived2 : boolean
+>someDerived : Derived1 | Derived2
+>Derived2 : typeof Derived2
+
+            someDerived.d
+>someDerived.d : string
+>someDerived : Derived2
+>d : string
+
+            break
+        default:
+            const never: never = someDerived;
+>never : never
+>someDerived : never
+    }
+
+    switch (true) {
+>true : true
+
+        case someDerived instanceof Derived1:
+>someDerived instanceof Derived1 : boolean
+>someDerived : Derived1 | Derived2
+>Derived1 : typeof Derived1
+
+            someDerived.d
+>someDerived.d : string
+>someDerived : Derived1
+>d : string
+
+            // fallthrough
+        case someDerived instanceof Derived2:
+>someDerived instanceof Derived2 : boolean
+>someDerived : Derived1 | Derived2
+>Derived2 : typeof Derived2
+
+            someDerived.d
+>someDerived.d : string
+>someDerived : Derived1 | Derived2
+>d : string
+
+            break
+        default:
+            const never: never = someDerived;
+>never : never
+>someDerived : never
+    }
+
+    switch (true) {
+>true : true
+
+        default:
+            const never: never = someDerived;
+>never : never
+>someDerived : never
+
+        case someDerived instanceof Derived1:
+>someDerived instanceof Derived1 : boolean
+>someDerived : Derived1 | Derived2
+>Derived1 : typeof Derived1
+
+            someDerived.d;
+>someDerived.d : string
+>someDerived : Derived1
+>d : string
+
+            someDerived.basey;
+>someDerived.basey : string
+>someDerived : Derived1
+>basey : string
+
+            break
+        case someDerived instanceof Derived2:
+>someDerived instanceof Derived2 : boolean
+>someDerived : Derived1 | Derived2
+>Derived2 : typeof Derived2
+
+            someDerived.d;
+>someDerived.d : string
+>someDerived : Derived2
+>d : string
+
+            someDerived.other;
+>someDerived.other : string
+>someDerived : Derived2
+>other : string
+    }
+
+    switch (true) {
+>true : true
+
+        case someDerived instanceof Derived1:
+>someDerived instanceof Derived1 : boolean
+>someDerived : Derived1 | Derived2
+>Derived1 : typeof Derived1
+
+            someDerived.d;
+>someDerived.d : string
+>someDerived : Derived1
+>d : string
+
+            someDerived.basey;
+>someDerived.basey : string
+>someDerived : Derived1
+>basey : string
+
+            break
+        default:
+            const never: never = someDerived;
+>never : never
+>someDerived : never
+
+        case someDerived instanceof Derived2:
+>someDerived instanceof Derived2 : boolean
+>someDerived : Derived1 | Derived2
+>Derived2 : typeof Derived2
+
+            someDerived.d;
+>someDerived.d : string
+>someDerived : Derived2
+>d : string
+
+            someDerived.other;
+>someDerived.other : string
+>someDerived : Derived2
+>other : string
+    }
+
+    switch (true) {
+>true : true
+
+        case someDerived instanceof Derived1:
+>someDerived instanceof Derived1 : boolean
+>someDerived : Derived1 | Derived2
+>Derived1 : typeof Derived1
+
+            someDerived.d;
+>someDerived.d : string
+>someDerived : Derived1
+>d : string
+
+            someDerived.basey;
+>someDerived.basey : string
+>someDerived : Derived1
+>basey : string
+
+            break
+        case someDerived instanceof Derived2:
+>someDerived instanceof Derived2 : boolean
+>someDerived : Derived1 | Derived2
+>Derived2 : typeof Derived2
+
+            someDerived.d;
+>someDerived.d : string
+>someDerived : Derived2
+>d : string
+
+            someDerived.other;
+>someDerived.other : string
+>someDerived : Derived2
+>other : string
+
+        default:
+            someDerived.d;
+>someDerived.d : string
+>someDerived : Derived2
+>d : string
+
+            someDerived.other;
+>someDerived.other : string
+>someDerived : Derived2
+>other : string
+
+            const never: never = someDerived;
+>never : never
+>someDerived : Derived2
+    }
+
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue8.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue8.symbols
new file mode 100644
index 0000000000000..ec14234e62b6c
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue8.symbols
@@ -0,0 +1,57 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue8.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue8.ts ===
+function foo(cond1: boolean, cond2: boolean) {
+>foo : Symbol(foo, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 0))
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 13))
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 28))
+
+    switch (true) {
+        case cond1:
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 13))
+
+            cond1; // Should be true
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 13))
+
+            //  ^?
+            cond2; // Should be boolean
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 28))
+
+            //  ^?
+            break;
+
+        case cond2:
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 28))
+
+            cond1; // Should be false?
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 13))
+
+            //  ^?
+            cond2; // Should be true
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 28))
+
+            //  ^?
+            break;
+
+        default:
+            cond1; // Should be false?
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 13))
+
+            //  ^?
+            cond2; // Should be false?
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 28))
+
+            //  ^?
+            break;
+    }
+
+    cond1; // Should be boolean
+>cond1 : Symbol(cond1, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 13))
+
+    //  ^?
+    cond2; // Should be boolean
+>cond2 : Symbol(cond2, Decl(narrowByClauseExpressionInSwitchTrue8.ts, 0, 28))
+
+    //  ^?
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue8.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue8.types
new file mode 100644
index 0000000000000..45230dc5e12b9
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue8.types
@@ -0,0 +1,59 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue8.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue8.ts ===
+function foo(cond1: boolean, cond2: boolean) {
+>foo : (cond1: boolean, cond2: boolean) => void
+>cond1 : boolean
+>cond2 : boolean
+
+    switch (true) {
+>true : true
+
+        case cond1:
+>cond1 : boolean
+
+            cond1; // Should be true
+>cond1 : true
+
+            //  ^?
+            cond2; // Should be boolean
+>cond2 : boolean
+
+            //  ^?
+            break;
+
+        case cond2:
+>cond2 : boolean
+
+            cond1; // Should be false?
+>cond1 : false
+
+            //  ^?
+            cond2; // Should be true
+>cond2 : true
+
+            //  ^?
+            break;
+
+        default:
+            cond1; // Should be false?
+>cond1 : false
+
+            //  ^?
+            cond2; // Should be false?
+>cond2 : false
+
+            //  ^?
+            break;
+    }
+
+    cond1; // Should be boolean
+>cond1 : boolean
+
+    //  ^?
+    cond2; // Should be boolean
+>cond2 : boolean
+
+    //  ^?
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue9.symbols b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue9.symbols
new file mode 100644
index 0000000000000..1cbdfc55b276d
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue9.symbols
@@ -0,0 +1,40 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue9.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue9.ts ===
+interface IProps {
+>IProps : Symbol(IProps, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 0, 0))
+
+    one: boolean;
+>one : Symbol(IProps.one, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 0, 18))
+}
+
+class Foo {
+>Foo : Symbol(Foo, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 2, 1))
+
+    mine: string = "";
+>mine : Symbol(Foo.mine, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 4, 11))
+
+    myMethod(x: IProps) {
+>myMethod : Symbol(Foo.myMethod, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 5, 22))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 7, 13))
+>IProps : Symbol(IProps, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 0, 0))
+
+        const { one } = x;
+>one : Symbol(one, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 8, 15))
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 7, 13))
+
+        switch (true) {
+            case one:
+>one : Symbol(one, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 8, 15))
+
+                break;
+            default:
+                let x = this.mine;
+>x : Symbol(x, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 13, 19))
+>this.mine : Symbol(Foo.mine, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 4, 11))
+>this : Symbol(Foo, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 2, 1))
+>mine : Symbol(Foo.mine, Decl(narrowByClauseExpressionInSwitchTrue9.ts, 4, 11))
+        }
+    }
+}
+
diff --git a/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue9.types b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue9.types
new file mode 100644
index 0000000000000..75557462a5b20
--- /dev/null
+++ b/tests/baselines/reference/narrowByClauseExpressionInSwitchTrue9.types
@@ -0,0 +1,40 @@
+//// [tests/cases/compiler/narrowByClauseExpressionInSwitchTrue9.ts] ////
+
+=== narrowByClauseExpressionInSwitchTrue9.ts ===
+interface IProps {
+    one: boolean;
+>one : boolean
+}
+
+class Foo {
+>Foo : Foo
+
+    mine: string = "";
+>mine : string
+>"" : ""
+
+    myMethod(x: IProps) {
+>myMethod : (x: IProps) => void
+>x : IProps
+
+        const { one } = x;
+>one : boolean
+>x : IProps
+
+        switch (true) {
+>true : true
+
+            case one:
+>one : boolean
+
+                break;
+            default:
+                let x = this.mine;
+>x : string
+>this.mine : string
+>this : this
+>mine : string
+        }
+    }
+}
+
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue1.ts
similarity index 100%
rename from tests/cases/compiler/narrowByClauseExpressionInSwitchTrue.ts
rename to tests/cases/compiler/narrowByClauseExpressionInSwitchTrue1.ts
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue10.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue10.ts
new file mode 100644
index 0000000000000..7d48369ca34e0
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue10.ts
@@ -0,0 +1,56 @@
+// @strict: true
+// @noEmit: true
+
+function foo(cond1: boolean, cond2: boolean) {
+    switch (true) {
+        case cond1 || cond2:
+            cond1; // boolean
+            //  ^?
+            cond2; // boolean
+            //  ^?
+            break;
+
+        case cond2:
+            cond1; // false
+            //  ^?
+            cond2;; // never
+            //  ^?
+            break;
+
+        default:
+            cond1; // false
+            //  ^?
+            cond2; // false
+            //  ^?
+            break;
+    }
+
+    cond1; // boolean
+    //  ^?
+    cond2; // boolean
+    //  ^?
+}
+
+function blah(cond1: boolean, cond2: boolean) {
+    if (cond1 || cond2) {
+        cond1; // boolean
+        //  ^?
+        cond2; // boolean
+        //  ^?
+    } else if (cond2) {
+        cond1; // false
+        //  ^?
+        cond2; // never
+        //  ^?
+    } else {
+        cond1; // false
+        //  ^?
+        cond2; // false
+        //  ^?
+    }
+
+    cond1; // boolean
+    //  ^?
+    cond2; // boolean
+    //  ^?
+}
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue2.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue2.ts
new file mode 100644
index 0000000000000..461e3505c393a
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue2.ts
@@ -0,0 +1,29 @@
+// @strict: true
+// @noEmit: true
+
+// https://github.com/microsoft/TypeScript/issues/55986
+
+declare const f: 'a' | 'b' | 'c';
+
+switch(true) {
+    case f === 'a':
+    case f === 'b':
+        f;
+        break
+    default:
+        f;
+}
+
+f;
+
+switch(true) {
+    case f === 'a':
+        f;
+    case f === 'b':
+        f;
+        break
+    default:
+        f;
+}
+
+f;
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue3.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue3.ts
new file mode 100644
index 0000000000000..d0dbafccbb108
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue3.ts
@@ -0,0 +1,22 @@
+// @strict: true
+// @noEmit: true
+
+type Shape =
+    | { kind: "circle", radius: number }
+    | { kind: "square", sideLength: number }
+
+function wat(shape: Shape) {
+    switch (true) {
+        case shape.kind === "circle":
+            return Math.PI * shape.radius ** 2;
+        case shape.kind === "circle": // should error
+    }
+
+    if (shape.kind === "circle") {
+        return Math.PI * shape.radius ** 2;
+    }
+    else if (shape.kind === "circle") {
+        //         ~~~~
+        // Property 'kind' does not exist on type 'never'.
+    }
+}
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue4.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue4.ts
new file mode 100644
index 0000000000000..15596fd7ad11a
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue4.ts
@@ -0,0 +1,12 @@
+// @strict: true
+// @noEmit: true
+
+declare const f: 'a' | 'b' | 'c';
+
+switch (true) {
+  case f === "a":
+  default:
+    f;
+  case f === "b":
+    f;
+}
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue5.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue5.ts
new file mode 100644
index 0000000000000..f4aee3ff151e1
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue5.ts
@@ -0,0 +1,133 @@
+// @strict: true
+// @noEmit: true
+
+type A = { kind: "A", value: number };
+type B = { kind: "B", name: string };
+type C = { kind: "C", cond: boolean };
+type D = { kind: "D", value: boolean };
+type E = { kind: "E", x: number, y: number };
+
+type All = A | B | C | D | E;
+
+function fn1switch(input: All) {
+    switch (true) {
+        case input.kind === "A":
+        case input.kind === "B":
+            if (input.kind === "A") {
+                return;
+            }
+
+            input; // Should be B;
+            //  ^?
+
+            // fallthrough
+        case input.kind === "C":
+            input; // Should be B | C
+            //  ^?
+            break;
+        default:
+            input; // Should be D | E
+            //  ^?
+    }
+
+    input; // Should not be A
+    //  ^?
+}
+
+function fn1ifelse(input: All) {
+    if (input.kind === "A" || input.kind === "B") {
+        if (input.kind === "A") {
+            return;
+        }
+
+        input; // Should be B;
+        //  ^?
+    }
+    if (input.kind === "C" || input.kind === "B") {
+        input; // Should be B | C
+        //  ^?
+    }
+    else {
+        input; // Should be D | E
+        //  ^?
+    }
+
+    input; // Should not be A
+    //  ^?
+}
+
+function fn2switch(input: All) {
+    switch (true) {
+        case input.kind === "A":
+        case input.kind === "B":
+            if (input.kind === "A") {
+                return;
+            }
+
+            input; // Should be B;
+            //  ^?
+
+            // fallthrough
+        case input.kind === "C":
+            input; // Should be B | C
+            //  ^?
+            break;
+        default:
+            input; // Should be D | E
+            //  ^?
+            return;
+    }
+
+    input; // Should be B | C
+    //  ^?
+}
+
+function fn2ifelse(input: All) {
+    if (input.kind === "A" || input.kind === "B") {
+        if (input.kind === "A") {
+            return;
+        }
+
+        input; // Should be B;
+        //  ^?
+    }
+    if (input.kind === "C" || input.kind === "B") {
+        input; // Should be B | C
+        //  ^?
+    }
+    else {
+        input; // Should be D | E
+        //  ^?
+        return;
+    }
+
+    input; // Should be B | C
+    //  ^?
+}
+
+function fn3switch(input: All) {
+    switch (true) {
+        case input.kind === "A":
+        case input.kind === "B":
+            if (input.kind === "A") {
+                return;
+            }
+
+            input; // Should be B;
+            //  ^?
+
+            // fallthrough
+        default:
+            input; // Should be B | D | E
+            //  ^?
+            break;
+
+        case input.kind === "C":
+            input; // Should be C
+            //  ^?
+            break;
+    }
+
+    input; // Should not be A
+    //  ^?
+}
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue6.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue6.ts
new file mode 100644
index 0000000000000..491355b79e906
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue6.ts
@@ -0,0 +1,78 @@
+// @strict: true
+// @noEmit: true
+
+interface A {
+    kind: "a";
+    aProps: string;
+}
+
+interface B {
+    kind: "b";
+    bProps: string;
+}
+
+interface C {
+    kind: "c";
+    cProps: string;
+}
+
+
+type MyType = A | B | C;
+
+function isA(x: MyType) {
+    switch (true) {
+        default:
+            const never: never = x;
+        case x.kind === "a":
+            x.aProps;
+            break;
+        case x.kind === "b":
+            x.bProps;
+            break;
+        case x.kind === "c":
+            x.cProps;
+            break;
+    }
+
+    switch (true) {
+        default:
+            const never: never = x;
+        case x.kind === "a": {
+            x.aProps;
+            break;
+        }
+        case x.kind === "b": {
+            x.bProps;
+            break;
+        }
+        case x.kind === "c": {
+            x.cProps;
+            break;
+        }
+    }
+    
+    switch (true) {
+        default:
+            x.aProps;
+            break;
+        case x.kind === "b":
+            x.bProps;
+            break;
+        case x.kind === "c":
+            x.cProps;
+            break;
+    }
+
+    switch (true) {
+        default:
+            const never: never = x;
+        case x.kind === "a":
+            x.aProps;
+            // fallthrough
+        case x.kind === "b":
+            x.bProps;
+            // fallthrough
+        case x.kind === "c":
+            x.cProps;
+    }
+}
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue7.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue7.ts
new file mode 100644
index 0000000000000..d482d8fa033a4
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue7.ts
@@ -0,0 +1,86 @@
+// @strict: true
+// @noEmit: true
+
+class Base {
+    basey: string = "";
+}
+
+class Derived1 extends Base {
+    d: string = "";
+}
+
+class Derived2 extends Base {
+    d: string = "";
+    other: string = "";
+}
+
+function classy(base: Base, someDerived: Derived1 | Derived2) {
+    switch (true) {
+        case base instanceof Derived1:
+            base.d
+            // fallthrough
+        default:
+            base.basey
+    }
+
+    switch (true) {
+        case someDerived instanceof Derived1:
+            someDerived.d
+            break;
+        case someDerived instanceof Derived2:
+            someDerived.d
+            break
+        default:
+            const never: never = someDerived;
+    }
+
+    switch (true) {
+        case someDerived instanceof Derived1:
+            someDerived.d
+            // fallthrough
+        case someDerived instanceof Derived2:
+            someDerived.d
+            break
+        default:
+            const never: never = someDerived;
+    }
+
+    switch (true) {
+        default:
+            const never: never = someDerived;
+        case someDerived instanceof Derived1:
+            someDerived.d;
+            someDerived.basey;
+            break
+        case someDerived instanceof Derived2:
+            someDerived.d;
+            someDerived.other;
+    }
+
+    switch (true) {
+        case someDerived instanceof Derived1:
+            someDerived.d;
+            someDerived.basey;
+            break
+        default:
+            const never: never = someDerived;
+        case someDerived instanceof Derived2:
+            someDerived.d;
+            someDerived.other;
+    }
+
+    switch (true) {
+        case someDerived instanceof Derived1:
+            someDerived.d;
+            someDerived.basey;
+            break
+        case someDerived instanceof Derived2:
+            someDerived.d;
+            someDerived.other;
+        default:
+            someDerived.d;
+            someDerived.other;
+            const never: never = someDerived;
+    }
+
+}
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue8.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue8.ts
new file mode 100644
index 0000000000000..3572817cba99b
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue8.ts
@@ -0,0 +1,32 @@
+// @strict: true
+// @noEmit: true
+
+function foo(cond1: boolean, cond2: boolean) {
+    switch (true) {
+        case cond1:
+            cond1; // Should be true
+            //  ^?
+            cond2; // Should be boolean
+            //  ^?
+            break;
+
+        case cond2:
+            cond1; // Should be false?
+            //  ^?
+            cond2; // Should be true
+            //  ^?
+            break;
+
+        default:
+            cond1; // Should be false?
+            //  ^?
+            cond2; // Should be false?
+            //  ^?
+            break;
+    }
+
+    cond1; // Should be boolean
+    //  ^?
+    cond2; // Should be boolean
+    //  ^?
+}
diff --git a/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue9.ts b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue9.ts
new file mode 100644
index 0000000000000..1f8942d90b1fb
--- /dev/null
+++ b/tests/cases/compiler/narrowByClauseExpressionInSwitchTrue9.ts
@@ -0,0 +1,20 @@
+// @strict: true
+// @noEmit: true
+
+interface IProps {
+    one: boolean;
+}
+
+class Foo {
+    mine: string = "";
+
+    myMethod(x: IProps) {
+        const { one } = x;
+        switch (true) {
+            case one:
+                break;
+            default:
+                let x = this.mine;
+        }
+    }
+}

From d1a2e7e730cb8ebd44662ece6b263e2d4d885da2 Mon Sep 17 00:00:00 2001
From: TypeScript Bot <typescriptbot@microsoft.com>
Date: Sat, 7 Oct 2023 06:18:08 +0000
Subject: [PATCH 2/7] Update package-lock.json

---
 package-lock.json | 56 +++++++++++++++++++++++------------------------
 1 file changed, 28 insertions(+), 28 deletions(-)

diff --git a/package-lock.json b/package-lock.json
index d78e55a1e51bb..b9ccfc450477b 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -578,9 +578,9 @@
             }
         },
         "node_modules/@eslint/js": {
-            "version": "8.50.0",
-            "resolved": "https://registry.npmjs.org/@eslint/js/-/js-8.50.0.tgz",
-            "integrity": "sha512-NCC3zz2+nvYd+Ckfh87rA47zfu2QsQpvc6k1yzTk+b9KzRj0wkGa8LSoGOXN6Zv4lRf/EIoZ80biDh9HOI+RNQ==",
+            "version": "8.51.0",
+            "resolved": "https://registry.npmjs.org/@eslint/js/-/js-8.51.0.tgz",
+            "integrity": "sha512-HxjQ8Qn+4SI3/AFv6sOrDB+g6PpUTDwSJiQqOrnneEk8L71161srI9gjzzZvYVbzHiVg/BvcH95+cK/zfIt4pg==",
             "dev": true,
             "engines": {
                 "node": "^12.22.0 || ^14.17.0 || >=16.0.0"
@@ -938,9 +938,9 @@
             "dev": true
         },
         "node_modules/@types/node": {
-            "version": "20.8.2",
-            "resolved": "https://registry.npmjs.org/@types/node/-/node-20.8.2.tgz",
-            "integrity": "sha512-Vvycsc9FQdwhxE3y3DzeIxuEJbWGDsnrxvMADzTDF/lcdR9/K+AQIeAghTQsHtotg/q0j3WEOYS/jQgSdWue3w==",
+            "version": "20.8.3",
+            "resolved": "https://registry.npmjs.org/@types/node/-/node-20.8.3.tgz",
+            "integrity": "sha512-jxiZQFpb+NlH5kjW49vXxvxTjeeqlbsnTAdBTKpzEdPs9itay7MscYXz3Fo9VYFEsfQ6LJFitHad3faerLAjCw==",
             "dev": true
         },
         "node_modules/@types/semver": {
@@ -1801,15 +1801,15 @@
             }
         },
         "node_modules/eslint": {
-            "version": "8.50.0",
-            "resolved": "https://registry.npmjs.org/eslint/-/eslint-8.50.0.tgz",
-            "integrity": "sha512-FOnOGSuFuFLv/Sa+FDVRZl4GGVAAFFi8LecRsI5a1tMO5HIE8nCm4ivAlzt4dT3ol/PaaGC0rJEEXQmHJBGoOg==",
+            "version": "8.51.0",
+            "resolved": "https://registry.npmjs.org/eslint/-/eslint-8.51.0.tgz",
+            "integrity": "sha512-2WuxRZBrlwnXi+/vFSJyjMqrNjtJqiasMzehF0shoLaW7DzS3/9Yvrmq5JiT66+pNjiX4UBnLDiKHcWAr/OInA==",
             "dev": true,
             "dependencies": {
                 "@eslint-community/eslint-utils": "^4.2.0",
                 "@eslint-community/regexpp": "^4.6.1",
                 "@eslint/eslintrc": "^2.1.2",
-                "@eslint/js": "8.50.0",
+                "@eslint/js": "8.51.0",
                 "@humanwhocodes/config-array": "^0.11.11",
                 "@humanwhocodes/module-importer": "^1.0.1",
                 "@nodelib/fs.walk": "^1.2.8",
@@ -2143,12 +2143,12 @@
             }
         },
         "node_modules/flat-cache": {
-            "version": "3.1.0",
-            "resolved": "https://registry.npmjs.org/flat-cache/-/flat-cache-3.1.0.tgz",
-            "integrity": "sha512-OHx4Qwrrt0E4jEIcI5/Xb+f+QmJYNj2rrK8wiIdQOIrB9WrrJL8cjZvXdXuBTkkEwEqLycb5BeZDV1o2i9bTew==",
+            "version": "3.1.1",
+            "resolved": "https://registry.npmjs.org/flat-cache/-/flat-cache-3.1.1.tgz",
+            "integrity": "sha512-/qM2b3LUIaIgviBQovTLvijfyOQXPtSRnRK26ksj2J7rzPIecePUIpJsZ4T02Qg+xiAEKIs5K8dsHEd+VaKa/Q==",
             "dev": true,
             "dependencies": {
-                "flatted": "^3.2.7",
+                "flatted": "^3.2.9",
                 "keyv": "^4.5.3",
                 "rimraf": "^3.0.2"
             },
@@ -4178,9 +4178,9 @@
             }
         },
         "@eslint/js": {
-            "version": "8.50.0",
-            "resolved": "https://registry.npmjs.org/@eslint/js/-/js-8.50.0.tgz",
-            "integrity": "sha512-NCC3zz2+nvYd+Ckfh87rA47zfu2QsQpvc6k1yzTk+b9KzRj0wkGa8LSoGOXN6Zv4lRf/EIoZ80biDh9HOI+RNQ==",
+            "version": "8.51.0",
+            "resolved": "https://registry.npmjs.org/@eslint/js/-/js-8.51.0.tgz",
+            "integrity": "sha512-HxjQ8Qn+4SI3/AFv6sOrDB+g6PpUTDwSJiQqOrnneEk8L71161srI9gjzzZvYVbzHiVg/BvcH95+cK/zfIt4pg==",
             "dev": true
         },
         "@humanwhocodes/config-array": {
@@ -4468,9 +4468,9 @@
             "dev": true
         },
         "@types/node": {
-            "version": "20.8.2",
-            "resolved": "https://registry.npmjs.org/@types/node/-/node-20.8.2.tgz",
-            "integrity": "sha512-Vvycsc9FQdwhxE3y3DzeIxuEJbWGDsnrxvMADzTDF/lcdR9/K+AQIeAghTQsHtotg/q0j3WEOYS/jQgSdWue3w==",
+            "version": "20.8.3",
+            "resolved": "https://registry.npmjs.org/@types/node/-/node-20.8.3.tgz",
+            "integrity": "sha512-jxiZQFpb+NlH5kjW49vXxvxTjeeqlbsnTAdBTKpzEdPs9itay7MscYXz3Fo9VYFEsfQ6LJFitHad3faerLAjCw==",
             "dev": true
         },
         "@types/semver": {
@@ -5087,15 +5087,15 @@
             "dev": true
         },
         "eslint": {
-            "version": "8.50.0",
-            "resolved": "https://registry.npmjs.org/eslint/-/eslint-8.50.0.tgz",
-            "integrity": "sha512-FOnOGSuFuFLv/Sa+FDVRZl4GGVAAFFi8LecRsI5a1tMO5HIE8nCm4ivAlzt4dT3ol/PaaGC0rJEEXQmHJBGoOg==",
+            "version": "8.51.0",
+            "resolved": "https://registry.npmjs.org/eslint/-/eslint-8.51.0.tgz",
+            "integrity": "sha512-2WuxRZBrlwnXi+/vFSJyjMqrNjtJqiasMzehF0shoLaW7DzS3/9Yvrmq5JiT66+pNjiX4UBnLDiKHcWAr/OInA==",
             "dev": true,
             "requires": {
                 "@eslint-community/eslint-utils": "^4.2.0",
                 "@eslint-community/regexpp": "^4.6.1",
                 "@eslint/eslintrc": "^2.1.2",
-                "@eslint/js": "8.50.0",
+                "@eslint/js": "8.51.0",
                 "@humanwhocodes/config-array": "^0.11.11",
                 "@humanwhocodes/module-importer": "^1.0.1",
                 "@nodelib/fs.walk": "^1.2.8",
@@ -5329,12 +5329,12 @@
             "dev": true
         },
         "flat-cache": {
-            "version": "3.1.0",
-            "resolved": "https://registry.npmjs.org/flat-cache/-/flat-cache-3.1.0.tgz",
-            "integrity": "sha512-OHx4Qwrrt0E4jEIcI5/Xb+f+QmJYNj2rrK8wiIdQOIrB9WrrJL8cjZvXdXuBTkkEwEqLycb5BeZDV1o2i9bTew==",
+            "version": "3.1.1",
+            "resolved": "https://registry.npmjs.org/flat-cache/-/flat-cache-3.1.1.tgz",
+            "integrity": "sha512-/qM2b3LUIaIgviBQovTLvijfyOQXPtSRnRK26ksj2J7rzPIecePUIpJsZ4T02Qg+xiAEKIs5K8dsHEd+VaKa/Q==",
             "dev": true,
             "requires": {
-                "flatted": "^3.2.7",
+                "flatted": "^3.2.9",
                 "keyv": "^4.5.3",
                 "rimraf": "^3.0.2"
             }

From 61a96b1641abe24c4adc3633eb936df89eb991f2 Mon Sep 17 00:00:00 2001
From: TypeScript Bot <typescriptbot@microsoft.com>
Date: Sun, 8 Oct 2023 06:19:04 +0000
Subject: [PATCH 3/7] Update package-lock.json

---
 package-lock.json | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/package-lock.json b/package-lock.json
index b9ccfc450477b..facac0374d15e 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -2654,9 +2654,9 @@
             "dev": true
         },
         "node_modules/keyv": {
-            "version": "4.5.3",
-            "resolved": "https://registry.npmjs.org/keyv/-/keyv-4.5.3.tgz",
-            "integrity": "sha512-QCiSav9WaX1PgETJ+SpNnx2PRRapJ/oRSXM4VO5OGYGSjrxbKPVFVhB3l2OCbLCk329N8qyAtsJjSjvVBWzEug==",
+            "version": "4.5.4",
+            "resolved": "https://registry.npmjs.org/keyv/-/keyv-4.5.4.tgz",
+            "integrity": "sha512-oxVHkHR/EJf2CNXnWxRLW6mg7JyCCUcG0DtEGmL2ctUo1PNTin1PUil+r/+4r5MpVgC/fn1kjsx7mjSujKqIpw==",
             "dev": true,
             "dependencies": {
                 "json-buffer": "3.0.1"
@@ -5705,9 +5705,9 @@
             "dev": true
         },
         "keyv": {
-            "version": "4.5.3",
-            "resolved": "https://registry.npmjs.org/keyv/-/keyv-4.5.3.tgz",
-            "integrity": "sha512-QCiSav9WaX1PgETJ+SpNnx2PRRapJ/oRSXM4VO5OGYGSjrxbKPVFVhB3l2OCbLCk329N8qyAtsJjSjvVBWzEug==",
+            "version": "4.5.4",
+            "resolved": "https://registry.npmjs.org/keyv/-/keyv-4.5.4.tgz",
+            "integrity": "sha512-oxVHkHR/EJf2CNXnWxRLW6mg7JyCCUcG0DtEGmL2ctUo1PNTin1PUil+r/+4r5MpVgC/fn1kjsx7mjSujKqIpw==",
             "dev": true,
             "requires": {
                 "json-buffer": "3.0.1"

From 9144836360cc6bb4e930baf7afd3aa9699572929 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mateusz=20Burzy=C5=84ski?= <mateuszburzynski@gmail.com>
Date: Mon, 9 Oct 2023 20:36:16 +0200
Subject: [PATCH 4/7] Fixed type narrowing in switch statements with
 parenthesized expressions (#56035)

---
 src/compiler/checker.ts                       |  2 +-
 ...rowByParenthesizedSwitchExpression.symbols | 66 +++++++++++++++++++
 ...arrowByParenthesizedSwitchExpression.types | 63 ++++++++++++++++++
 .../narrowByParenthesizedSwitchExpression.ts  | 32 +++++++++
 4 files changed, 162 insertions(+), 1 deletion(-)
 create mode 100644 tests/baselines/reference/narrowByParenthesizedSwitchExpression.symbols
 create mode 100644 tests/baselines/reference/narrowByParenthesizedSwitchExpression.types
 create mode 100644 tests/cases/compiler/narrowByParenthesizedSwitchExpression.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 2c9344679abd8..4c31ece8602d0 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -27446,7 +27446,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         }
 
         function getTypeAtSwitchClause(flow: FlowSwitchClause): FlowType {
-            const expr = flow.switchStatement.expression;
+            const expr = skipParentheses(flow.switchStatement.expression);
             const flowType = getTypeAtFlowNode(flow.antecedent);
             let type = getTypeFromFlowType(flowType);
             if (isMatchingReference(reference, expr)) {
diff --git a/tests/baselines/reference/narrowByParenthesizedSwitchExpression.symbols b/tests/baselines/reference/narrowByParenthesizedSwitchExpression.symbols
new file mode 100644
index 0000000000000..4bcf3c49d1644
--- /dev/null
+++ b/tests/baselines/reference/narrowByParenthesizedSwitchExpression.symbols
@@ -0,0 +1,66 @@
+//// [tests/cases/compiler/narrowByParenthesizedSwitchExpression.ts] ////
+
+=== narrowByParenthesizedSwitchExpression.ts ===
+interface Base {
+>Base : Symbol(Base, Decl(narrowByParenthesizedSwitchExpression.ts, 0, 0))
+
+  type: "foo" | "bar";
+>type : Symbol(Base.type, Decl(narrowByParenthesizedSwitchExpression.ts, 0, 16))
+}
+
+interface Foo extends Base {
+>Foo : Symbol(Foo, Decl(narrowByParenthesizedSwitchExpression.ts, 2, 1))
+>Base : Symbol(Base, Decl(narrowByParenthesizedSwitchExpression.ts, 0, 0))
+
+  type: "foo";
+>type : Symbol(Foo.type, Decl(narrowByParenthesizedSwitchExpression.ts, 4, 28))
+
+  foo: string;
+>foo : Symbol(Foo.foo, Decl(narrowByParenthesizedSwitchExpression.ts, 5, 14))
+}
+
+interface Bar extends Base {
+>Bar : Symbol(Bar, Decl(narrowByParenthesizedSwitchExpression.ts, 7, 1))
+>Base : Symbol(Base, Decl(narrowByParenthesizedSwitchExpression.ts, 0, 0))
+
+  type: "bar";
+>type : Symbol(Bar.type, Decl(narrowByParenthesizedSwitchExpression.ts, 9, 28))
+
+  bar: number;
+>bar : Symbol(Bar.bar, Decl(narrowByParenthesizedSwitchExpression.ts, 10, 14))
+}
+
+function getV(): Foo | Bar {
+>getV : Symbol(getV, Decl(narrowByParenthesizedSwitchExpression.ts, 12, 1))
+>Foo : Symbol(Foo, Decl(narrowByParenthesizedSwitchExpression.ts, 2, 1))
+>Bar : Symbol(Bar, Decl(narrowByParenthesizedSwitchExpression.ts, 7, 1))
+
+  return null!;
+}
+
+const v = getV();
+>v : Symbol(v, Decl(narrowByParenthesizedSwitchExpression.ts, 18, 5))
+>getV : Symbol(getV, Decl(narrowByParenthesizedSwitchExpression.ts, 12, 1))
+
+switch ((v.type)) {
+>v.type : Symbol(type, Decl(narrowByParenthesizedSwitchExpression.ts, 4, 28), Decl(narrowByParenthesizedSwitchExpression.ts, 9, 28))
+>v : Symbol(v, Decl(narrowByParenthesizedSwitchExpression.ts, 18, 5))
+>type : Symbol(type, Decl(narrowByParenthesizedSwitchExpression.ts, 4, 28), Decl(narrowByParenthesizedSwitchExpression.ts, 9, 28))
+
+  case "bar":
+    v.bar;
+>v.bar : Symbol(Bar.bar, Decl(narrowByParenthesizedSwitchExpression.ts, 10, 14))
+>v : Symbol(v, Decl(narrowByParenthesizedSwitchExpression.ts, 18, 5))
+>bar : Symbol(Bar.bar, Decl(narrowByParenthesizedSwitchExpression.ts, 10, 14))
+
+    break;
+
+  case "foo":
+    v.foo;
+>v.foo : Symbol(Foo.foo, Decl(narrowByParenthesizedSwitchExpression.ts, 5, 14))
+>v : Symbol(v, Decl(narrowByParenthesizedSwitchExpression.ts, 18, 5))
+>foo : Symbol(Foo.foo, Decl(narrowByParenthesizedSwitchExpression.ts, 5, 14))
+
+    break;
+}
+
diff --git a/tests/baselines/reference/narrowByParenthesizedSwitchExpression.types b/tests/baselines/reference/narrowByParenthesizedSwitchExpression.types
new file mode 100644
index 0000000000000..6601417a33c13
--- /dev/null
+++ b/tests/baselines/reference/narrowByParenthesizedSwitchExpression.types
@@ -0,0 +1,63 @@
+//// [tests/cases/compiler/narrowByParenthesizedSwitchExpression.ts] ////
+
+=== narrowByParenthesizedSwitchExpression.ts ===
+interface Base {
+  type: "foo" | "bar";
+>type : "foo" | "bar"
+}
+
+interface Foo extends Base {
+  type: "foo";
+>type : "foo"
+
+  foo: string;
+>foo : string
+}
+
+interface Bar extends Base {
+  type: "bar";
+>type : "bar"
+
+  bar: number;
+>bar : number
+}
+
+function getV(): Foo | Bar {
+>getV : () => Foo | Bar
+
+  return null!;
+>null! : never
+}
+
+const v = getV();
+>v : Foo | Bar
+>getV() : Foo | Bar
+>getV : () => Foo | Bar
+
+switch ((v.type)) {
+>(v.type) : "foo" | "bar"
+>v.type : "foo" | "bar"
+>v : Foo | Bar
+>type : "foo" | "bar"
+
+  case "bar":
+>"bar" : "bar"
+
+    v.bar;
+>v.bar : number
+>v : Bar
+>bar : number
+
+    break;
+
+  case "foo":
+>"foo" : "foo"
+
+    v.foo;
+>v.foo : string
+>v : Foo
+>foo : string
+
+    break;
+}
+
diff --git a/tests/cases/compiler/narrowByParenthesizedSwitchExpression.ts b/tests/cases/compiler/narrowByParenthesizedSwitchExpression.ts
new file mode 100644
index 0000000000000..2f2d9330ce1d8
--- /dev/null
+++ b/tests/cases/compiler/narrowByParenthesizedSwitchExpression.ts
@@ -0,0 +1,32 @@
+// @strict: true
+// @noEmit: true
+
+interface Base {
+  type: "foo" | "bar";
+}
+
+interface Foo extends Base {
+  type: "foo";
+  foo: string;
+}
+
+interface Bar extends Base {
+  type: "bar";
+  bar: number;
+}
+
+function getV(): Foo | Bar {
+  return null!;
+}
+
+const v = getV();
+
+switch ((v.type)) {
+  case "bar":
+    v.bar;
+    break;
+
+  case "foo":
+    v.foo;
+    break;
+}

From d0d406747d580ec4972dc411a9f158c232695987 Mon Sep 17 00:00:00 2001
From: Andrew Branch <andrewbranch@users.noreply.github.com>
Date: Mon, 9 Oct 2023 11:38:15 -0700
Subject: [PATCH 5/7] Add type reference directive for all visited references
 to ambient modules (#56015)

---
 src/compiler/checker.ts                       |  5 +++
 src/compiler/emitter.ts                       |  1 +
 src/compiler/transformers/declarations.ts     | 27 ++++++++++++++--
 src/compiler/types.ts                         |  1 +
 src/compiler/utilities.ts                     |  5 ++-
 ...larationEmitBundleWithAmbientReferences.js |  1 +
 ...onEmitTripleSlashReferenceAmbientModule.js | 31 +++++++++++++++++++
 ...ImportHelpersCollisions2(module=node16).js |  1 +
 ...portHelpersCollisions2(module=nodenext).js |  1 +
 ...ModulesImportAssignments(module=node16).js |  3 ++
 ...dulesImportAssignments(module=nodenext).js |  3 ++
 ...ImportHelpersCollisions2(module=node16).js |  2 ++
 ...portHelpersCollisions2(module=nodenext).js |  2 ++
 ...ImportHelpersCollisions3(module=node16).js |  2 ++
 ...portHelpersCollisions3(module=nodenext).js |  2 ++
 ...onEmitTripleSlashReferenceAmbientModule.ts | 20 ++++++++++++
 16 files changed, 104 insertions(+), 3 deletions(-)
 create mode 100644 tests/baselines/reference/declarationEmitTripleSlashReferenceAmbientModule.js
 create mode 100644 tests/cases/compiler/declarationEmitTripleSlashReferenceAmbientModule.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 4c31ece8602d0..6098245cb6c67 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -47930,6 +47930,11 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                 return !sym.exports ? [] : nodeBuilder.symbolTableToDeclarationStatements(sym.exports, node, flags, tracker, bundled);
             },
             isImportRequiredByAugmentation,
+            tryFindAmbientModule: moduleReferenceExpression => {
+                const node = getParseTreeNode(moduleReferenceExpression);
+                const moduleSpecifier = node && isStringLiteralLike(node) ? node.text : undefined;
+                return moduleSpecifier !== undefined ? tryFindAmbientModule(moduleSpecifier, /*withAugmentations*/ true) : undefined;
+            },
         };
 
         function isImportRequiredByAugmentation(node: ImportDeclaration) {
diff --git a/src/compiler/emitter.ts b/src/compiler/emitter.ts
index 3d035053761af..463651bdb0049 100644
--- a/src/compiler/emitter.ts
+++ b/src/compiler/emitter.ts
@@ -1182,6 +1182,7 @@ export const notImplementedResolver: EmitResolver = {
     isBindingCapturedByNode: notImplemented,
     getDeclarationStatementsForSourceFile: notImplemented,
     isImportRequiredByAugmentation: notImplemented,
+    tryFindAmbientModule: notImplemented,
 };
 
 /**
diff --git a/src/compiler/transformers/declarations.ts b/src/compiler/transformers/declarations.ts
index 05b5ad1c8b9b4..512c2eb4704f8 100644
--- a/src/compiler/transformers/declarations.ts
+++ b/src/compiler/transformers/declarations.ts
@@ -212,6 +212,7 @@ import {
     TransformationContext,
     transformNodes,
     tryCast,
+    tryGetModuleSpecifierFromDeclaration,
     TypeAliasDeclaration,
     TypeNode,
     TypeParameterDeclaration,
@@ -345,6 +346,18 @@ export function transformDeclarations(context: TransformationContext) {
         refs.set(getOriginalNodeId(container), container);
     }
 
+    function trackReferencedAmbientModuleFromImport(node: ImportDeclaration | ExportDeclaration | ImportEqualsDeclaration | ImportTypeNode) {
+        const moduleSpecifier = tryGetModuleSpecifierFromDeclaration(node);
+        const symbol = moduleSpecifier && resolver.tryFindAmbientModule(moduleSpecifier);
+        if (symbol?.declarations) {
+            for (const decl of symbol.declarations) {
+                if (isAmbientModule(decl) && getSourceFileOfNode(decl) !== currentSourceFile) {
+                    trackReferencedAmbientModule(decl, symbol);
+                }
+            }
+        }
+    }
+
     function handleSymbolAccessibilityError(symbolAccessibilityResult: SymbolAccessibilityResult) {
         if (symbolAccessibilityResult.accessibility === SymbolAccessibility.Accessible) {
             // Add aliases back onto the possible imports list if they're not there so we can try them again with updated visibility info
@@ -1312,6 +1325,7 @@ export function transformDeclarations(context: TransformationContext) {
                 }
                 case SyntaxKind.ImportType: {
                     if (!isLiteralImportTypeNode(input)) return cleanup(input);
+                    trackReferencedAmbientModuleFromImport(input);
                     return cleanup(factory.updateImportTypeNode(
                         input,
                         factory.updateLiteralTypeNode(input.argument, rewriteModuleSpecifier(input, input.argument.literal)),
@@ -1370,6 +1384,7 @@ export function transformDeclarations(context: TransformationContext) {
                 }
                 resultHasScopeMarker = true;
                 // Always visible if the parent node isn't dropped for being not visible
+                trackReferencedAmbientModuleFromImport(input);
                 // Rewrite external module names if necessary
                 return factory.updateExportDeclaration(
                     input,
@@ -1456,10 +1471,18 @@ export function transformDeclarations(context: TransformationContext) {
         if (shouldStripInternal(input)) return;
         switch (input.kind) {
             case SyntaxKind.ImportEqualsDeclaration: {
-                return transformImportEqualsDeclaration(input);
+                const transformed = transformImportEqualsDeclaration(input);
+                if (transformed) {
+                    trackReferencedAmbientModuleFromImport(input);
+                }
+                return transformed;
             }
             case SyntaxKind.ImportDeclaration: {
-                return transformImportDeclaration(input);
+                const transformed = transformImportDeclaration(input);
+                if (transformed) {
+                    trackReferencedAmbientModuleFromImport(input);
+                }
+                return transformed;
             }
         }
         if (isDeclaration(input) && isDeclarationAndNotVisible(input)) return;
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index 9a185a4923249..a64c4c86b596d 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -5675,6 +5675,7 @@ export interface EmitResolver {
     isBindingCapturedByNode(node: Node, decl: VariableDeclaration | BindingElement): boolean;
     getDeclarationStatementsForSourceFile(node: SourceFile, flags: NodeBuilderFlags, tracker: SymbolTracker, bundled?: boolean): Statement[] | undefined;
     isImportRequiredByAugmentation(decl: ImportDeclaration): boolean;
+    tryFindAmbientModule(moduleReferenceExpression: Expression): Symbol | undefined;
 }
 
 // dprint-ignore
diff --git a/src/compiler/utilities.ts b/src/compiler/utilities.ts
index 126b74d91dac7..8d4a3d2496993 100644
--- a/src/compiler/utilities.ts
+++ b/src/compiler/utilities.ts
@@ -3975,12 +3975,13 @@ export function isFunctionSymbol(symbol: Symbol | undefined) {
 }
 
 /** @internal */
-export function tryGetModuleSpecifierFromDeclaration(node: AnyImportOrBareOrAccessedRequire | AliasDeclarationNode): StringLiteralLike | undefined {
+export function tryGetModuleSpecifierFromDeclaration(node: AnyImportOrBareOrAccessedRequire | AliasDeclarationNode | ExportDeclaration | ImportTypeNode): StringLiteralLike | undefined {
     switch (node.kind) {
         case SyntaxKind.VariableDeclaration:
         case SyntaxKind.BindingElement:
             return findAncestor(node.initializer, (node): node is RequireOrImportCall => isRequireCall(node, /*requireStringLiteralLikeArgument*/ true))?.arguments[0];
         case SyntaxKind.ImportDeclaration:
+        case SyntaxKind.ExportDeclaration:
             return tryCast(node.moduleSpecifier, isStringLiteralLike);
         case SyntaxKind.ImportEqualsDeclaration:
             return tryCast(tryCast(node.moduleReference, isExternalModuleReference)?.expression, isStringLiteralLike);
@@ -3992,6 +3993,8 @@ export function tryGetModuleSpecifierFromDeclaration(node: AnyImportOrBareOrAcce
             return tryCast(node.parent.parent.moduleSpecifier, isStringLiteralLike);
         case SyntaxKind.ImportSpecifier:
             return tryCast(node.parent.parent.parent.moduleSpecifier, isStringLiteralLike);
+        case SyntaxKind.ImportType:
+            return isLiteralImportTypeNode(node) ? node.argument.literal : undefined;
         default:
             Debug.assertNever(node);
     }
diff --git a/tests/baselines/reference/declarationEmitBundleWithAmbientReferences.js b/tests/baselines/reference/declarationEmitBundleWithAmbientReferences.js
index 0d6946277ad26..ece01c1794a0b 100644
--- a/tests/baselines/reference/declarationEmitBundleWithAmbientReferences.js
+++ b/tests/baselines/reference/declarationEmitBundleWithAmbientReferences.js
@@ -37,6 +37,7 @@ define("conditional_directive_field", ["require", "exports"], function (require,
 
 
 //// [datastore.bundle.d.ts]
+/// <reference path="../lib/lib.d.ts" />
 declare module "datastore_result" {
     import { Result } from "lib/result";
     export type T<T> = Result<Error, T>;
diff --git a/tests/baselines/reference/declarationEmitTripleSlashReferenceAmbientModule.js b/tests/baselines/reference/declarationEmitTripleSlashReferenceAmbientModule.js
new file mode 100644
index 0000000000000..b283b08edcd9e
--- /dev/null
+++ b/tests/baselines/reference/declarationEmitTripleSlashReferenceAmbientModule.js
@@ -0,0 +1,31 @@
+//// [tests/cases/compiler/declarationEmitTripleSlashReferenceAmbientModule.ts] ////
+
+//// [index.d.ts]
+declare module "url" {
+  export class Url {}
+  export function parse(): Url; 
+}
+
+//// [usage1.ts]
+export { parse } from "url";
+
+//// [usage2.ts]
+import { parse } from "url";
+export const thing: import("url").Url = parse(); 
+
+//// [usage3.ts]
+import { parse } from "url";
+export const thing = parse();
+
+
+
+
+//// [usage1.d.ts]
+/// <reference types="node" />
+export { parse } from "url";
+//// [usage2.d.ts]
+/// <reference types="node" />
+export declare const thing: import("url").Url;
+//// [usage3.d.ts]
+/// <reference types="node" />
+export declare const thing: import("url").Url;
diff --git a/tests/baselines/reference/nodeModulesAllowJsImportHelpersCollisions2(module=node16).js b/tests/baselines/reference/nodeModulesAllowJsImportHelpersCollisions2(module=node16).js
index 7c584a828615c..0d0046de24daa 100644
--- a/tests/baselines/reference/nodeModulesAllowJsImportHelpersCollisions2(module=node16).js
+++ b/tests/baselines/reference/nodeModulesAllowJsImportHelpersCollisions2(module=node16).js
@@ -40,6 +40,7 @@ export * as fs from "fs";
 
 
 //// [index.d.ts]
+/// <reference path="../../types.d.ts" />
 export * from "fs";
 export * as fs from "fs";
 //// [index.d.ts]
diff --git a/tests/baselines/reference/nodeModulesAllowJsImportHelpersCollisions2(module=nodenext).js b/tests/baselines/reference/nodeModulesAllowJsImportHelpersCollisions2(module=nodenext).js
index 7c584a828615c..0d0046de24daa 100644
--- a/tests/baselines/reference/nodeModulesAllowJsImportHelpersCollisions2(module=nodenext).js
+++ b/tests/baselines/reference/nodeModulesAllowJsImportHelpersCollisions2(module=nodenext).js
@@ -40,6 +40,7 @@ export * as fs from "fs";
 
 
 //// [index.d.ts]
+/// <reference path="../../types.d.ts" />
 export * from "fs";
 export * as fs from "fs";
 //// [index.d.ts]
diff --git a/tests/baselines/reference/nodeModulesImportAssignments(module=node16).js b/tests/baselines/reference/nodeModulesImportAssignments(module=node16).js
index e56ab00bb87c4..779a5236c5d5d 100644
--- a/tests/baselines/reference/nodeModulesImportAssignments(module=node16).js
+++ b/tests/baselines/reference/nodeModulesImportAssignments(module=node16).js
@@ -58,8 +58,11 @@ export { fs2 };
 
 
 //// [index.d.ts]
+/// <reference path="../types.d.ts" />
 export import fs2 = require("fs");
 //// [index.d.ts]
+/// <reference path="types.d.ts" />
 export import fs2 = require("fs");
 //// [file.d.ts]
+/// <reference path="types.d.ts" />
 export import fs2 = require("fs");
diff --git a/tests/baselines/reference/nodeModulesImportAssignments(module=nodenext).js b/tests/baselines/reference/nodeModulesImportAssignments(module=nodenext).js
index e56ab00bb87c4..779a5236c5d5d 100644
--- a/tests/baselines/reference/nodeModulesImportAssignments(module=nodenext).js
+++ b/tests/baselines/reference/nodeModulesImportAssignments(module=nodenext).js
@@ -58,8 +58,11 @@ export { fs2 };
 
 
 //// [index.d.ts]
+/// <reference path="../types.d.ts" />
 export import fs2 = require("fs");
 //// [index.d.ts]
+/// <reference path="types.d.ts" />
 export import fs2 = require("fs");
 //// [file.d.ts]
+/// <reference path="types.d.ts" />
 export import fs2 = require("fs");
diff --git a/tests/baselines/reference/nodeModulesImportHelpersCollisions2(module=node16).js b/tests/baselines/reference/nodeModulesImportHelpersCollisions2(module=node16).js
index e8e9b78464c55..53eeb9bd5a78a 100644
--- a/tests/baselines/reference/nodeModulesImportHelpersCollisions2(module=node16).js
+++ b/tests/baselines/reference/nodeModulesImportHelpersCollisions2(module=node16).js
@@ -40,8 +40,10 @@ export * as fs from "fs";
 
 
 //// [index.d.ts]
+/// <reference path="../types.d.ts" />
 export * from "fs";
 export * as fs from "fs";
 //// [index.d.ts]
+/// <reference path="types.d.ts" />
 export * from "fs";
 export * as fs from "fs";
diff --git a/tests/baselines/reference/nodeModulesImportHelpersCollisions2(module=nodenext).js b/tests/baselines/reference/nodeModulesImportHelpersCollisions2(module=nodenext).js
index e8e9b78464c55..53eeb9bd5a78a 100644
--- a/tests/baselines/reference/nodeModulesImportHelpersCollisions2(module=nodenext).js
+++ b/tests/baselines/reference/nodeModulesImportHelpersCollisions2(module=nodenext).js
@@ -40,8 +40,10 @@ export * as fs from "fs";
 
 
 //// [index.d.ts]
+/// <reference path="../types.d.ts" />
 export * from "fs";
 export * as fs from "fs";
 //// [index.d.ts]
+/// <reference path="types.d.ts" />
 export * from "fs";
 export * as fs from "fs";
diff --git a/tests/baselines/reference/nodeModulesImportHelpersCollisions3(module=node16).js b/tests/baselines/reference/nodeModulesImportHelpersCollisions3(module=node16).js
index 8abf8ba9adac3..5f98164aaaa84 100644
--- a/tests/baselines/reference/nodeModulesImportHelpersCollisions3(module=node16).js
+++ b/tests/baselines/reference/nodeModulesImportHelpersCollisions3(module=node16).js
@@ -39,6 +39,8 @@ export { default } from "fs";
 
 
 //// [index.d.ts]
+/// <reference path="../types.d.ts" />
 export { default } from "fs";
 //// [index.d.ts]
+/// <reference path="types.d.ts" />
 export { default } from "fs";
diff --git a/tests/baselines/reference/nodeModulesImportHelpersCollisions3(module=nodenext).js b/tests/baselines/reference/nodeModulesImportHelpersCollisions3(module=nodenext).js
index 8abf8ba9adac3..5f98164aaaa84 100644
--- a/tests/baselines/reference/nodeModulesImportHelpersCollisions3(module=nodenext).js
+++ b/tests/baselines/reference/nodeModulesImportHelpersCollisions3(module=nodenext).js
@@ -39,6 +39,8 @@ export { default } from "fs";
 
 
 //// [index.d.ts]
+/// <reference path="../types.d.ts" />
 export { default } from "fs";
 //// [index.d.ts]
+/// <reference path="types.d.ts" />
 export { default } from "fs";
diff --git a/tests/cases/compiler/declarationEmitTripleSlashReferenceAmbientModule.ts b/tests/cases/compiler/declarationEmitTripleSlashReferenceAmbientModule.ts
new file mode 100644
index 0000000000000..df9274fa371e2
--- /dev/null
+++ b/tests/cases/compiler/declarationEmitTripleSlashReferenceAmbientModule.ts
@@ -0,0 +1,20 @@
+// @declaration: true
+// @emitDeclarationOnly: true
+// @noTypesAndSymbols: true
+
+// @Filename: /node_modules/@types/node/index.d.ts
+declare module "url" {
+  export class Url {}
+  export function parse(): Url; 
+}
+
+// @Filename: /usage1.ts
+export { parse } from "url";
+
+// @Filename: /usage2.ts
+import { parse } from "url";
+export const thing: import("url").Url = parse(); 
+
+// @Filename: /usage3.ts
+import { parse } from "url";
+export const thing = parse();

From 3516ca96e552ba82c4c7d9215adba4afc53eeedc Mon Sep 17 00:00:00 2001
From: Sheetal Nandi <shkamat@microsoft.com>
Date: Mon, 9 Oct 2023 16:05:11 -0700
Subject: [PATCH 6/7] pass program update level to getExternalFiles in tsserver
 plugins so plugins can make decision about their cache based on that (#56047)

Co-authored-by: Andrew Branch <andrewbranch@users.noreply.github.com>
---
 src/compiler/tsbuildPublic.ts                 | 54 +++++++-------
 src/compiler/watchPublic.ts                   | 42 +++++------
 src/compiler/watchUtilities.ts                | 18 +++--
 src/server/editorServices.ts                  | 60 +++++++--------
 src/server/project.ts                         | 36 ++++-----
 .../unittests/tsserver/externalProjects.ts    |  6 +-
 src/testRunner/unittests/tsserver/plugins.ts  | 21 +++++-
 tests/baselines/reference/api/typescript.d.ts | 17 ++++-
 ...on-ts-extensions-with-wildcard-matching.js | 74 +++++++++++++++++--
 9 files changed, 213 insertions(+), 115 deletions(-)

diff --git a/src/compiler/tsbuildPublic.ts b/src/compiler/tsbuildPublic.ts
index 8512e52f07f86..070ad30f4c04b 100644
--- a/src/compiler/tsbuildPublic.ts
+++ b/src/compiler/tsbuildPublic.ts
@@ -14,7 +14,6 @@ import {
     CompilerHost,
     CompilerOptions,
     CompilerOptionsValue,
-    ConfigFileProgramReloadLevel,
     convertToRelativePath,
     copyProperties,
     createCompilerDiagnostic,
@@ -95,6 +94,7 @@ import {
     ProgramBundleEmitBuildInfo,
     ProgramHost,
     ProgramMultiFileEmitBuildInfo,
+    ProgramUpdateLevel,
     readBuilderProgram,
     ReadBuildProgramHost,
     resolveConfigFileProjectName,
@@ -287,7 +287,7 @@ export interface SolutionBuilder<T extends BuilderProgram> {
 
     // Testing only
     /** @internal */ getUpToDateStatusOfProject(project: string): UpToDateStatus;
-    /** @internal */ invalidateProject(configFilePath: ResolvedConfigFilePath, reloadLevel?: ConfigFileProgramReloadLevel): void;
+    /** @internal */ invalidateProject(configFilePath: ResolvedConfigFilePath, updateLevel?: ProgramUpdateLevel): void;
     /** @internal */ close(): void;
 }
 
@@ -389,7 +389,7 @@ interface SolutionBuilderState<T extends BuilderProgram> extends WatchFactory<Wa
 
     readonly builderPrograms: Map<ResolvedConfigFilePath, T>;
     readonly diagnostics: Map<ResolvedConfigFilePath, readonly Diagnostic[]>;
-    readonly projectPendingBuild: Map<ResolvedConfigFilePath, ConfigFileProgramReloadLevel>;
+    readonly projectPendingBuild: Map<ResolvedConfigFilePath, ProgramUpdateLevel>;
     readonly projectErrorsReported: Map<ResolvedConfigFilePath, true>;
 
     readonly compilerHost: CompilerHost & ReadBuildProgramHost;
@@ -795,13 +795,13 @@ function clearProjectStatus<T extends BuilderProgram>(state: SolutionBuilderStat
     state.diagnostics.delete(resolved);
 }
 
-function addProjToQueue<T extends BuilderProgram>({ projectPendingBuild }: SolutionBuilderState<T>, proj: ResolvedConfigFilePath, reloadLevel: ConfigFileProgramReloadLevel) {
+function addProjToQueue<T extends BuilderProgram>({ projectPendingBuild }: SolutionBuilderState<T>, proj: ResolvedConfigFilePath, updateLevel: ProgramUpdateLevel) {
     const value = projectPendingBuild.get(proj);
     if (value === undefined) {
-        projectPendingBuild.set(proj, reloadLevel);
+        projectPendingBuild.set(proj, updateLevel);
     }
-    else if (value < reloadLevel) {
-        projectPendingBuild.set(proj, reloadLevel);
+    else if (value < updateLevel) {
+        projectPendingBuild.set(proj, updateLevel);
     }
 }
 
@@ -815,7 +815,7 @@ function setupInitialBuild<T extends BuilderProgram>(state: SolutionBuilderState
     buildOrder.forEach(configFileName =>
         state.projectPendingBuild.set(
             toResolvedConfigFilePath(state, configFileName),
-            ConfigFileProgramReloadLevel.None,
+            ProgramUpdateLevel.Update,
         )
     );
 
@@ -1402,8 +1402,8 @@ function getNextInvalidatedProjectCreateInfo<T extends BuilderProgram>(
     for (let projectIndex = 0; projectIndex < buildOrder.length; projectIndex++) {
         const project = buildOrder[projectIndex];
         const projectPath = toResolvedConfigFilePath(state, project);
-        const reloadLevel = state.projectPendingBuild.get(projectPath);
-        if (reloadLevel === undefined) continue;
+        const updateLevel = state.projectPendingBuild.get(projectPath);
+        if (updateLevel === undefined) continue;
 
         if (reportQueue) {
             reportQueue = false;
@@ -1417,14 +1417,14 @@ function getNextInvalidatedProjectCreateInfo<T extends BuilderProgram>(
             continue;
         }
 
-        if (reloadLevel === ConfigFileProgramReloadLevel.Full) {
+        if (updateLevel === ProgramUpdateLevel.Full) {
             watchConfigFile(state, project, projectPath, config);
             watchExtendedConfigFiles(state, projectPath, config);
             watchWildCardDirectories(state, project, projectPath, config);
             watchInputFiles(state, project, projectPath, config);
             watchPackageJsonFiles(state, project, projectPath, config);
         }
-        else if (reloadLevel === ConfigFileProgramReloadLevel.Partial) {
+        else if (updateLevel === ProgramUpdateLevel.RootNamesAndUpdate) {
             // Update file names
             config.fileNames = getFileNamesFromConfigSpecs(config.options.configFile!.configFileSpecs!, getDirectoryPath(project), config.options, state.parseConfigFileHost);
             updateErrorForNoInputFiles(config.fileNames, project, config.options.configFile!.configFileSpecs!, config.errors, canJsonReportNoInputFiles(config.raw));
@@ -2169,7 +2169,7 @@ function queueReferencingProjects<T extends BuilderProgram>(
                         break;
                 }
             }
-            addProjToQueue(state, nextProjectPath, ConfigFileProgramReloadLevel.None);
+            addProjToQueue(state, nextProjectPath, ProgramUpdateLevel.Update);
             break;
         }
     }
@@ -2251,7 +2251,7 @@ function cleanWorker<T extends BuilderProgram>(state: SolutionBuilderState<T>, p
                 }
                 else {
                     host.deleteFile(output);
-                    invalidateProject(state, resolvedPath, ConfigFileProgramReloadLevel.None);
+                    invalidateProject(state, resolvedPath, ProgramUpdateLevel.Update);
                 }
             }
         }
@@ -2264,24 +2264,24 @@ function cleanWorker<T extends BuilderProgram>(state: SolutionBuilderState<T>, p
     return ExitStatus.Success;
 }
 
-function invalidateProject<T extends BuilderProgram>(state: SolutionBuilderState<T>, resolved: ResolvedConfigFilePath, reloadLevel: ConfigFileProgramReloadLevel) {
+function invalidateProject<T extends BuilderProgram>(state: SolutionBuilderState<T>, resolved: ResolvedConfigFilePath, updateLevel: ProgramUpdateLevel) {
     // If host implements getParsedCommandLine, we cant get list of files from parseConfigFileHost
-    if (state.host.getParsedCommandLine && reloadLevel === ConfigFileProgramReloadLevel.Partial) {
-        reloadLevel = ConfigFileProgramReloadLevel.Full;
+    if (state.host.getParsedCommandLine && updateLevel === ProgramUpdateLevel.RootNamesAndUpdate) {
+        updateLevel = ProgramUpdateLevel.Full;
     }
-    if (reloadLevel === ConfigFileProgramReloadLevel.Full) {
+    if (updateLevel === ProgramUpdateLevel.Full) {
         state.configFileCache.delete(resolved);
         state.buildOrder = undefined;
     }
     state.needsSummary = true;
     clearProjectStatus(state, resolved);
-    addProjToQueue(state, resolved, reloadLevel);
+    addProjToQueue(state, resolved, updateLevel);
     enableCache(state);
 }
 
-function invalidateProjectAndScheduleBuilds<T extends BuilderProgram>(state: SolutionBuilderState<T>, resolvedPath: ResolvedConfigFilePath, reloadLevel: ConfigFileProgramReloadLevel) {
+function invalidateProjectAndScheduleBuilds<T extends BuilderProgram>(state: SolutionBuilderState<T>, resolvedPath: ResolvedConfigFilePath, updateLevel: ProgramUpdateLevel) {
     state.reportFileChangeDetected = true;
-    invalidateProject(state, resolvedPath, reloadLevel);
+    invalidateProject(state, resolvedPath, updateLevel);
     scheduleBuildInvalidatedProject(state, 250, /*changeDetected*/ true);
 }
 
@@ -2344,7 +2344,7 @@ function watchConfigFile<T extends BuilderProgram>(state: SolutionBuilderState<T
         watchFile(
             state,
             resolved,
-            () => invalidateProjectAndScheduleBuilds(state, resolvedPath, ConfigFileProgramReloadLevel.Full),
+            () => invalidateProjectAndScheduleBuilds(state, resolvedPath, ProgramUpdateLevel.Full),
             PollingInterval.High,
             parsed?.watchOptions,
             WatchType.ConfigFile,
@@ -2362,7 +2362,7 @@ function watchExtendedConfigFiles<T extends BuilderProgram>(state: SolutionBuild
             watchFile(
                 state,
                 extendedConfigFileName,
-                () => state.allWatchedExtendedConfigFiles.get(extendedConfigFilePath)?.projects.forEach(projectConfigFilePath => invalidateProjectAndScheduleBuilds(state, projectConfigFilePath, ConfigFileProgramReloadLevel.Full)),
+                () => state.allWatchedExtendedConfigFiles.get(extendedConfigFilePath)?.projects.forEach(projectConfigFilePath => invalidateProjectAndScheduleBuilds(state, projectConfigFilePath, ProgramUpdateLevel.Full)),
                 PollingInterval.High,
                 parsed?.watchOptions,
                 WatchType.ExtendedConfigFile,
@@ -2395,7 +2395,7 @@ function watchWildCardDirectories<T extends BuilderProgram>(state: SolutionBuild
                         })
                     ) return;
 
-                    invalidateProjectAndScheduleBuilds(state, resolvedPath, ConfigFileProgramReloadLevel.Partial);
+                    invalidateProjectAndScheduleBuilds(state, resolvedPath, ProgramUpdateLevel.RootNamesAndUpdate);
                 },
                 flags,
                 parsed?.watchOptions,
@@ -2415,7 +2415,7 @@ function watchInputFiles<T extends BuilderProgram>(state: SolutionBuilderState<T
                 watchFile(
                     state,
                     input,
-                    () => invalidateProjectAndScheduleBuilds(state, resolvedPath, ConfigFileProgramReloadLevel.None),
+                    () => invalidateProjectAndScheduleBuilds(state, resolvedPath, ProgramUpdateLevel.Update),
                     PollingInterval.Low,
                     parsed?.watchOptions,
                     WatchType.SourceFile,
@@ -2436,7 +2436,7 @@ function watchPackageJsonFiles<T extends BuilderProgram>(state: SolutionBuilderS
                 watchFile(
                     state,
                     path,
-                    () => invalidateProjectAndScheduleBuilds(state, resolvedPath, ConfigFileProgramReloadLevel.None),
+                    () => invalidateProjectAndScheduleBuilds(state, resolvedPath, ProgramUpdateLevel.Update),
                     PollingInterval.High,
                     parsed?.watchOptions,
                     WatchType.PackageJson,
@@ -2503,7 +2503,7 @@ function createSolutionBuilderWorker<T extends BuilderProgram>(watch: boolean, h
             const configFilePath = toResolvedConfigFilePath(state, configFileName);
             return getUpToDateStatus(state, parseConfigFile(state, configFileName, configFilePath), configFilePath);
         },
-        invalidateProject: (configFilePath, reloadLevel) => invalidateProject(state, configFilePath, reloadLevel || ConfigFileProgramReloadLevel.None),
+        invalidateProject: (configFilePath, updateLevel) => invalidateProject(state, configFilePath, updateLevel || ProgramUpdateLevel.Update),
         close: () => stopWatching(state),
     };
 }
diff --git a/src/compiler/watchPublic.ts b/src/compiler/watchPublic.ts
index 135c8bdc53887..ac2c666ea8986 100644
--- a/src/compiler/watchPublic.ts
+++ b/src/compiler/watchPublic.ts
@@ -12,7 +12,6 @@ import {
     CompilerHost,
     CompilerOptions,
     ConfigFileDiagnosticsReporter,
-    ConfigFileProgramReloadLevel,
     createBuilderProgramUsingProgramBuildInfo,
     createCachedDirectoryStructureHost,
     createCompilerDiagnostic,
@@ -64,6 +63,7 @@ import {
     Path,
     perfLogger,
     PollingInterval,
+    ProgramUpdateLevel,
     ProjectReference,
     ResolutionCache,
     ResolutionCacheHost,
@@ -399,8 +399,8 @@ interface ParsedConfig {
     watcher?: FileWatcher;
     /** Wild card directories watched from this config file */
     watchedDirectories?: Map<string, WildcardDirectoryWatcher>;
-    /** Reload to be done for this config file */
-    reloadLevel?: ConfigFileProgramReloadLevel.Partial | ConfigFileProgramReloadLevel.Full;
+    /** Level of program update to be done for this config file */
+    updateLevel?: ProgramUpdateLevel.RootNamesAndUpdate | ProgramUpdateLevel.Full;
 }
 
 // All of one and partial of the other, or vice versa.
@@ -431,7 +431,7 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
     type HostFileInfo = FilePresentOnHost | FileMissingOnHost | FilePresenceUnknownOnHost;
 
     let builderProgram: T;
-    let reloadLevel: ConfigFileProgramReloadLevel; // level to indicate if the program needs to be reloaded from config file/just filenames etc
+    let updateLevel: ProgramUpdateLevel; // level to indicate if the program needs to be reloaded from config file/just filenames etc
     let missingFilesMap: Map<Path, FileWatcher>; // Map of file watchers for the missing files
     let watchedWildcardDirectories: Map<string, WildcardDirectoryWatcher>; // map of watchers for the wild card directories in the config file
     let timerToUpdateProgram: any; // timer callback to recompile the program
@@ -872,7 +872,7 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
 
     function scheduleProgramReload() {
         Debug.assert(!!configFileName);
-        reloadLevel = ConfigFileProgramReloadLevel.Full;
+        updateLevel = ProgramUpdateLevel.Full;
         scheduleProgramUpdate();
     }
 
@@ -883,12 +883,12 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
     }
 
     function updateProgram() {
-        switch (reloadLevel) {
-            case ConfigFileProgramReloadLevel.Partial:
+        switch (updateLevel) {
+            case ProgramUpdateLevel.RootNamesAndUpdate:
                 perfLogger?.logStartUpdateProgram("PartialConfigReload");
                 reloadFileNamesFromConfigFile();
                 break;
-            case ConfigFileProgramReloadLevel.Full:
+            case ProgramUpdateLevel.Full:
                 perfLogger?.logStartUpdateProgram("FullConfigReload");
                 reloadConfigFile();
                 break;
@@ -907,7 +907,7 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
         Debug.assert(compilerOptions);
         Debug.assert(configFileName);
 
-        reloadLevel = ConfigFileProgramReloadLevel.None;
+        updateLevel = ProgramUpdateLevel.Update;
         rootFileNames = getFileNamesFromConfigSpecs(compilerOptions.configFile!.configFileSpecs!, getNormalizedAbsolutePath(getDirectoryPath(configFileName), currentDirectory), compilerOptions, parseConfigFileHost, extraFileExtensions);
         if (updateErrorForNoInputFiles(rootFileNames, getNormalizedAbsolutePath(configFileName, currentDirectory), compilerOptions.configFile!.configFileSpecs!, configFileParsingDiagnostics!, canConfigFileJsonReportNoInputFiles)) {
             hasChangedConfigFileParsingErrors = true;
@@ -920,7 +920,7 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
     function reloadConfigFile() {
         Debug.assert(configFileName);
         writeLog(`Reloading config file: ${configFileName}`);
-        reloadLevel = ConfigFileProgramReloadLevel.None;
+        updateLevel = ProgramUpdateLevel.Update;
 
         if (cachedDirectoryStructureHost) {
             cachedDirectoryStructureHost.clearCache();
@@ -965,9 +965,9 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
         const configPath = toPath(configFileName);
         let config = parsedConfigs?.get(configPath);
         if (config) {
-            if (!config.reloadLevel) return config.parsedCommandLine;
+            if (!config.updateLevel) return config.parsedCommandLine;
             // With host implementing getParsedCommandLine we cant just update file names
-            if (config.parsedCommandLine && config.reloadLevel === ConfigFileProgramReloadLevel.Partial && !host.getParsedCommandLine) {
+            if (config.parsedCommandLine && config.updateLevel === ProgramUpdateLevel.RootNamesAndUpdate && !host.getParsedCommandLine) {
                 writeLog("Reloading new file names and options");
                 Debug.assert(compilerOptions);
                 const fileNames = getFileNamesFromConfigSpecs(
@@ -977,7 +977,7 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
                     parseConfigFileHost,
                 );
                 config.parsedCommandLine = { ...config.parsedCommandLine, fileNames };
-                config.reloadLevel = undefined;
+                config.updateLevel = undefined;
                 return config.parsedCommandLine;
             }
         }
@@ -988,7 +988,7 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
             getParsedCommandLineFromConfigFileHost(configFileName);
         if (config) {
             config.parsedCommandLine = parsedCommandLine;
-            config.reloadLevel = undefined;
+            config.updateLevel = undefined;
         }
         else {
             (parsedConfigs ||= new Map()).set(configPath, config = { parsedCommandLine });
@@ -1120,8 +1120,8 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
                 ) return;
 
                 // Reload is pending, do the reload
-                if (reloadLevel !== ConfigFileProgramReloadLevel.Full) {
-                    reloadLevel = ConfigFileProgramReloadLevel.Partial;
+                if (updateLevel !== ProgramUpdateLevel.Full) {
+                    updateLevel = ProgramUpdateLevel.RootNamesAndUpdate;
 
                     // Schedule Update the program
                     scheduleProgramUpdate();
@@ -1152,12 +1152,12 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
                         projects.forEach(projectPath => {
                             if (configFileName && toPath(configFileName) === projectPath) {
                                 // If this is the config file of the project, reload completely
-                                reloadLevel = ConfigFileProgramReloadLevel.Full;
+                                updateLevel = ProgramUpdateLevel.Full;
                             }
                             else {
                                 // Reload config for the referenced projects and remove the resolutions from referenced projects since the config file changed
                                 const config = parsedConfigs?.get(projectPath);
-                                if (config) config.reloadLevel = ConfigFileProgramReloadLevel.Full;
+                                if (config) config.updateLevel = ProgramUpdateLevel.Full;
                                 resolutionCache.removeResolutionsFromProjectReferenceRedirects(projectPath);
                             }
                             scheduleProgramUpdate();
@@ -1178,7 +1178,7 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
             (_fileName, eventKind) => {
                 updateCachedSystemWithFile(configFileName, configPath, eventKind);
                 const config = parsedConfigs?.get(configPath);
-                if (config) config.reloadLevel = ConfigFileProgramReloadLevel.Full;
+                if (config) config.updateLevel = ProgramUpdateLevel.Full;
                 resolutionCache.removeResolutionsFromProjectReferenceRedirects(configPath);
                 scheduleProgramUpdate();
             },
@@ -1220,8 +1220,8 @@ export function createWatchProgram<T extends BuilderProgram>(host: WatchCompiler
                             ) return;
 
                             // Reload is pending, do the reload
-                            if (config.reloadLevel !== ConfigFileProgramReloadLevel.Full) {
-                                config.reloadLevel = ConfigFileProgramReloadLevel.Partial;
+                            if (config.updateLevel !== ProgramUpdateLevel.Full) {
+                                config.updateLevel = ProgramUpdateLevel.RootNamesAndUpdate;
 
                                 // Schedule Update the program
                                 scheduleProgramUpdate();
diff --git a/src/compiler/watchUtilities.ts b/src/compiler/watchUtilities.ts
index 422ec2f70be4c..c259f2ac9db95 100644
--- a/src/compiler/watchUtilities.ts
+++ b/src/compiler/watchUtilities.ts
@@ -365,12 +365,18 @@ export function createCachedDirectoryStructureHost(host: DirectoryStructureHost,
     }
 }
 
-/** @internal */
-export enum ConfigFileProgramReloadLevel {
-    None,
-    /** Update the file name list from the disk */
-    Partial,
-    /** Reload completely by re-reading contents of config file from disk and updating program */
+export enum ProgramUpdateLevel {
+    /** Program is updated with same root file names and options */
+    Update,
+    /** Loads program after updating root file names from the disk */
+    RootNamesAndUpdate,
+    /**
+     * Loads program completely, including:
+     *  - re-reading contents of config file from disk
+     *  - calculating root file names for the program
+     *  - Updating the program
+     */
+
     Full,
 }
 
diff --git a/src/server/editorServices.ts b/src/server/editorServices.ts
index 9f3da93b674c8..976ce0a27cb38 100644
--- a/src/server/editorServices.ts
+++ b/src/server/editorServices.ts
@@ -14,7 +14,6 @@ import {
     CommandLineOption,
     CompilerOptions,
     CompletionInfo,
-    ConfigFileProgramReloadLevel,
     contains,
     containsPath,
     convertCompilerOptionsForTelemetry,
@@ -95,6 +94,7 @@ import {
     PerformanceEvent,
     PluginImport,
     PollingInterval,
+    ProgramUpdateLevel,
     ProjectPackageJsonInfo,
     ProjectReference,
     ReadMapFile,
@@ -874,7 +874,7 @@ export interface ParsedConfig {
      * true if watchedDirectories need to be updated as per parsedCommandLine's updated watched directories
      */
     watchedDirectoriesStale?: boolean;
-    reloadLevel?: ConfigFileProgramReloadLevel.Partial | ConfigFileProgramReloadLevel.Full;
+    updateLevel?: ProgramUpdateLevel.RootNamesAndUpdate | ProgramUpdateLevel.Full;
 }
 
 function createProjectNameFactoryWithCounter(nameFactory: (counter: number) => string) {
@@ -1671,7 +1671,7 @@ export class ProjectService {
                 ) return;
 
                 // Reload is pending, do the reload
-                if (config.reloadLevel !== ConfigFileProgramReloadLevel.Full) config.reloadLevel = ConfigFileProgramReloadLevel.Partial;
+                if (config.updateLevel !== ProgramUpdateLevel.Full) config.updateLevel = ProgramUpdateLevel.RootNamesAndUpdate;
                 config.projects.forEach((watchWildcardDirectories, projectCanonicalPath) => {
                     if (!watchWildcardDirectories) return;
                     const project = this.getConfiguredProjectByCanonicalConfigFilePath(projectCanonicalPath);
@@ -1679,23 +1679,23 @@ export class ProjectService {
 
                     // Load root file names for configured project with the config file name
                     // But only schedule update if project references this config file
-                    const reloadLevel = configuredProjectForConfig === project ? ConfigFileProgramReloadLevel.Partial : ConfigFileProgramReloadLevel.None;
-                    if (project.pendingReload !== undefined && project.pendingReload > reloadLevel) return;
+                    const updateLevel = configuredProjectForConfig === project ? ProgramUpdateLevel.RootNamesAndUpdate : ProgramUpdateLevel.Update;
+                    if (project.pendingUpdateLevel !== undefined && project.pendingUpdateLevel > updateLevel) return;
 
                     // don't trigger callback on open, existing files
                     if (this.openFiles.has(fileOrDirectoryPath)) {
                         const info = Debug.checkDefined(this.getScriptInfoForPath(fileOrDirectoryPath));
                         if (info.isAttached(project)) {
-                            const loadLevelToSet = Math.max(reloadLevel, project.openFileWatchTriggered.get(fileOrDirectoryPath) || ConfigFileProgramReloadLevel.None) as ConfigFileProgramReloadLevel;
+                            const loadLevelToSet = Math.max(updateLevel, project.openFileWatchTriggered.get(fileOrDirectoryPath) || ProgramUpdateLevel.Update) as ProgramUpdateLevel;
                             project.openFileWatchTriggered.set(fileOrDirectoryPath, loadLevelToSet);
                         }
                         else {
-                            project.pendingReload = reloadLevel;
+                            project.pendingUpdateLevel = updateLevel;
                             this.delayUpdateProjectGraphAndEnsureProjectStructureForOpenFiles(project);
                         }
                     }
                     else {
-                        project.pendingReload = reloadLevel;
+                        project.pendingUpdateLevel = updateLevel;
                         this.delayUpdateProjectGraphAndEnsureProjectStructureForOpenFiles(project);
                     }
                 });
@@ -1708,12 +1708,12 @@ export class ProjectService {
     }
 
     /** @internal */
-    private delayUpdateProjectsFromParsedConfigOnConfigFileChange(canonicalConfigFilePath: NormalizedPath, reloadReason: string) {
+    private delayUpdateProjectsFromParsedConfigOnConfigFileChange(canonicalConfigFilePath: NormalizedPath, loadReason: string) {
         const configFileExistenceInfo = this.configFileExistenceInfoCache.get(canonicalConfigFilePath);
         if (!configFileExistenceInfo?.config) return false;
         let scheduledAnyProjectUpdate = false;
         // Update projects watching cached config
-        configFileExistenceInfo.config.reloadLevel = ConfigFileProgramReloadLevel.Full;
+        configFileExistenceInfo.config.updateLevel = ProgramUpdateLevel.Full;
 
         configFileExistenceInfo.config.projects.forEach((_watchWildcardDirectories, projectCanonicalPath) => {
             const project = this.getConfiguredProjectByCanonicalConfigFilePath(projectCanonicalPath);
@@ -1723,8 +1723,8 @@ export class ProjectService {
             if (projectCanonicalPath === canonicalConfigFilePath) {
                 // Skip refresh if project is not yet loaded
                 if (project.isInitialLoadPending()) return;
-                project.pendingReload = ConfigFileProgramReloadLevel.Full;
-                project.pendingReloadReason = reloadReason;
+                project.pendingUpdateLevel = ProgramUpdateLevel.Full;
+                project.pendingUpdateReason = loadReason;
                 this.delayUpdateProjectGraph(project);
             }
             else {
@@ -1922,11 +1922,11 @@ export class ProjectService {
 
                 // If project had open file affecting
                 // Reload the root Files from config if its not already scheduled
-                const reloadLevel = p.openFileWatchTriggered.get(info.path);
-                if (reloadLevel !== undefined) {
+                const updateLevel = p.openFileWatchTriggered.get(info.path);
+                if (updateLevel !== undefined) {
                     p.openFileWatchTriggered.delete(info.path);
-                    if (p.pendingReload !== undefined && p.pendingReload < reloadLevel) {
-                        p.pendingReload = reloadLevel;
+                    if (p.pendingUpdateLevel !== undefined && p.pendingUpdateLevel < updateLevel) {
+                        p.pendingUpdateLevel = updateLevel;
                         p.markFileAsDirty(info.path);
                     }
                 }
@@ -2438,7 +2438,7 @@ export class ProjectService {
             configFileExistenceInfo.config = {
                 cachedDirectoryStructureHost: createCachedDirectoryStructureHost(this.host, this.host.getCurrentDirectory(), this.host.useCaseSensitiveFileNames)!,
                 projects: new Map(),
-                reloadLevel: ConfigFileProgramReloadLevel.Full,
+                updateLevel: ProgramUpdateLevel.Full,
             };
         }
 
@@ -2457,8 +2457,8 @@ export class ProjectService {
     /** @internal */
     private createConfiguredProjectWithDelayLoad(configFileName: NormalizedPath, reason: string) {
         const project = this.createConfiguredProject(configFileName);
-        project.pendingReload = ConfigFileProgramReloadLevel.Full;
-        project.pendingReloadReason = reason;
+        project.pendingUpdateLevel = ProgramUpdateLevel.Full;
+        project.pendingUpdateReason = reason;
         return project;
     }
 
@@ -2521,7 +2521,7 @@ export class ProjectService {
             this.watchWildcards(configFilename, configFileExistenceInfo, project);
         }
         project.enablePluginsWithOptions(compilerOptions);
-        const filesToAdd = parsedCommandLine.fileNames.concat(project.getExternalFiles());
+        const filesToAdd = parsedCommandLine.fileNames.concat(project.getExternalFiles(ProgramUpdateLevel.Full));
         this.updateRootAndOptionsOfNonInferredProject(project, filesToAdd, fileNamePropertyReader, compilerOptions, parsedCommandLine.typeAcquisition!, parsedCommandLine.compileOnSave, parsedCommandLine.watchOptions);
         tracing?.pop();
     }
@@ -2529,8 +2529,8 @@ export class ProjectService {
     /** @internal */
     ensureParsedConfigUptoDate(configFilename: NormalizedPath, canonicalConfigFilePath: NormalizedPath, configFileExistenceInfo: ConfigFileExistenceInfo, forProject: ConfiguredProject): ConfigFileExistenceInfo {
         if (configFileExistenceInfo.config) {
-            if (!configFileExistenceInfo.config.reloadLevel) return configFileExistenceInfo;
-            if (configFileExistenceInfo.config.reloadLevel === ConfigFileProgramReloadLevel.Partial) {
+            if (!configFileExistenceInfo.config.updateLevel) return configFileExistenceInfo;
+            if (configFileExistenceInfo.config.updateLevel === ProgramUpdateLevel.RootNamesAndUpdate) {
                 this.reloadFileNamesOfParsedConfig(configFilename, configFileExistenceInfo.config);
                 return configFileExistenceInfo;
             }
@@ -2580,7 +2580,7 @@ export class ProjectService {
         else {
             configFileExistenceInfo.config.parsedCommandLine = parsedCommandLine;
             configFileExistenceInfo.config.watchedDirectoriesStale = true;
-            configFileExistenceInfo.config.reloadLevel = undefined;
+            configFileExistenceInfo.config.updateLevel = undefined;
         }
 
         // If watch options different than older options when setting for the first time, update the config file watcher
@@ -2761,14 +2761,14 @@ export class ProjectService {
     reloadFileNamesOfConfiguredProject(project: ConfiguredProject) {
         const fileNames = this.reloadFileNamesOfParsedConfig(project.getConfigFilePath(), this.configFileExistenceInfoCache.get(project.canonicalConfigFilePath)!.config!);
         project.updateErrorOnNoInputFiles(fileNames);
-        this.updateNonInferredProjectFiles(project, fileNames.concat(project.getExternalFiles()), fileNamePropertyReader);
+        this.updateNonInferredProjectFiles(project, fileNames.concat(project.getExternalFiles(ProgramUpdateLevel.RootNamesAndUpdate)), fileNamePropertyReader);
         return project.updateGraph();
     }
 
     /** @internal */
     private reloadFileNamesOfParsedConfig(configFileName: NormalizedPath, config: ParsedConfig) {
-        if (config.reloadLevel === undefined) return config.parsedCommandLine!.fileNames;
-        Debug.assert(config.reloadLevel === ConfigFileProgramReloadLevel.Partial);
+        if (config.updateLevel === undefined) return config.parsedCommandLine!.fileNames;
+        Debug.assert(config.updateLevel === ProgramUpdateLevel.RootNamesAndUpdate);
         const configFileSpecs = config.parsedCommandLine!.options.configFile!.configFileSpecs!;
         const fileNames = getFileNamesFromConfigSpecs(
             configFileSpecs,
@@ -3398,7 +3398,7 @@ export class ProjectService {
                     this.configuredProjects.forEach(project => {
                         if (
                             project.hasExternalProjectRef() &&
-                            project.pendingReload === ConfigFileProgramReloadLevel.Full &&
+                            project.pendingUpdateLevel === ProgramUpdateLevel.Full &&
                             !this.pendingProjectUpdates.has(project.getProjectName())
                         ) {
                             project.updateGraph();
@@ -3468,7 +3468,7 @@ export class ProjectService {
 
         // Ensure everything is reloaded for cached configs
         this.configFileExistenceInfoCache.forEach(info => {
-            if (info.config) info.config.reloadLevel = ConfigFileProgramReloadLevel.Full;
+            if (info.config) info.config.updateLevel = ProgramUpdateLevel.Full;
         });
 
         // Reload Projects
@@ -3517,8 +3517,8 @@ export class ProjectService {
                 if (!updatedProjects.has(project.canonicalConfigFilePath)) {
                     updatedProjects.set(project.canonicalConfigFilePath, true);
                     if (delayReload) {
-                        project.pendingReload = ConfigFileProgramReloadLevel.Full;
-                        project.pendingReloadReason = reason;
+                        project.pendingUpdateLevel = ProgramUpdateLevel.Full;
+                        project.pendingUpdateReason = reason;
                         if (clearSemanticCache) this.clearSemanticCache(project);
                         this.delayUpdateProjectGraph(project);
                     }
diff --git a/src/server/project.ts b/src/server/project.ts
index 8bffa1f281a86..5293e06fa540b 100644
--- a/src/server/project.ts
+++ b/src/server/project.ts
@@ -17,7 +17,6 @@ import {
     CompilerHost,
     CompilerOptions,
     concatenate,
-    ConfigFileProgramReloadLevel,
     containsPath,
     createCacheableExportInfoMap,
     createLanguageService,
@@ -98,6 +97,7 @@ import {
     PluginImport,
     PollingInterval,
     Program,
+    ProgramUpdateLevel,
     ProjectPackageJsonInfo,
     ProjectReference,
     removeFileExtension,
@@ -254,7 +254,7 @@ export interface PluginCreateInfo {
 
 export interface PluginModule {
     create(createInfo: PluginCreateInfo): LanguageService;
-    getExternalFiles?(proj: Project): string[];
+    getExternalFiles?(proj: Project, updateLevel: ProgramUpdateLevel): string[];
     onConfigurationChanged?(config: any): void;
 }
 
@@ -1027,11 +1027,11 @@ export abstract class Project implements LanguageServiceHost, ModuleResolutionHo
         return { ...newTypeAcquisition, include: this.removeExistingTypings(newTypeAcquisition.include) };
     }
 
-    getExternalFiles(): SortedReadonlyArray<string> {
+    getExternalFiles(updateLevel?: ProgramUpdateLevel): SortedReadonlyArray<string> {
         return sort(flatMap(this.plugins, plugin => {
             if (typeof plugin.module.getExternalFiles !== "function") return;
             try {
-                return plugin.module.getExternalFiles(this);
+                return plugin.module.getExternalFiles(this, updateLevel || ProgramUpdateLevel.Update);
             }
             catch (e) {
                 this.projectService.logger.info(`A plugin threw an exception in getExternalFiles: ${e}`);
@@ -1892,10 +1892,10 @@ export abstract class Project implements LanguageServiceHost, ModuleResolutionHo
             }
             // compute and return the difference
             const lastReportedFileNames = this.lastReportedFileNames;
-            const externalFiles = this.getExternalFiles().map((f): protocol.FileWithProjectReferenceRedirectInfo => ({
+            const externalFiles = this.externalFiles?.map((f): protocol.FileWithProjectReferenceRedirectInfo => ({
                 fileName: toNormalizedPath(f),
                 isSourceOfProjectReferenceRedirect: false,
-            }));
+            })) || emptyArray;
             const currentFiles = arrayToMap(
                 this.getFileNamesWithRedirectInfo(!!includeProjectReferenceRedirectInfo).concat(externalFiles),
                 info => info.fileName,
@@ -1945,10 +1945,10 @@ export abstract class Project implements LanguageServiceHost, ModuleResolutionHo
         else {
             // unknown version - return everything
             const projectFileNames = this.getFileNamesWithRedirectInfo(!!includeProjectReferenceRedirectInfo);
-            const externalFiles = this.getExternalFiles().map((f): protocol.FileWithProjectReferenceRedirectInfo => ({
+            const externalFiles = this.externalFiles?.map((f): protocol.FileWithProjectReferenceRedirectInfo => ({
                 fileName: toNormalizedPath(f),
                 isSourceOfProjectReferenceRedirect: false,
-            }));
+            })) || emptyArray;
             const allFiles = projectFileNames.concat(externalFiles);
             this.lastReportedFileNames = arrayToMap(
                 allFiles,
@@ -2679,12 +2679,12 @@ export class AutoImportProviderProject extends Project {
  */
 export class ConfiguredProject extends Project {
     /** @internal */
-    pendingReload: ConfigFileProgramReloadLevel | undefined;
+    pendingUpdateLevel: ProgramUpdateLevel | undefined;
     /** @internal */
-    pendingReloadReason: string | undefined;
+    pendingUpdateReason: string | undefined;
 
     /** @internal */
-    openFileWatchTriggered = new Map<string, ConfigFileProgramReloadLevel>();
+    openFileWatchTriggered = new Map<string, ProgramUpdateLevel>();
 
     /** @internal */
     canConfigFileJsonReportNoInputFiles = false;
@@ -2775,18 +2775,18 @@ export class ConfiguredProject extends Project {
     override updateGraph(): boolean {
         const isInitialLoad = this.isInitialLoadPending();
         this.isInitialLoadPending = returnFalse;
-        const reloadLevel = this.pendingReload;
-        this.pendingReload = ConfigFileProgramReloadLevel.None;
+        const updateLevel = this.pendingUpdateLevel;
+        this.pendingUpdateLevel = ProgramUpdateLevel.Update;
         let result: boolean;
-        switch (reloadLevel) {
-            case ConfigFileProgramReloadLevel.Partial:
+        switch (updateLevel) {
+            case ProgramUpdateLevel.RootNamesAndUpdate:
                 this.openFileWatchTriggered.clear();
                 result = this.projectService.reloadFileNamesOfConfiguredProject(this);
                 break;
-            case ConfigFileProgramReloadLevel.Full:
+            case ProgramUpdateLevel.Full:
                 this.openFileWatchTriggered.clear();
-                const reason = Debug.checkDefined(this.pendingReloadReason);
-                this.pendingReloadReason = undefined;
+                const reason = Debug.checkDefined(this.pendingUpdateReason);
+                this.pendingUpdateReason = undefined;
                 this.projectService.reloadConfiguredProject(this, reason, isInitialLoad, /*clearSemanticCache*/ false);
                 result = true;
                 break;
diff --git a/src/testRunner/unittests/tsserver/externalProjects.ts b/src/testRunner/unittests/tsserver/externalProjects.ts
index 5c6727ba5310d..62653cd49a235 100644
--- a/src/testRunner/unittests/tsserver/externalProjects.ts
+++ b/src/testRunner/unittests/tsserver/externalProjects.ts
@@ -685,10 +685,10 @@ describe("unittests:: tsserver:: externalProjects", () => {
             options: {},
         } as ts.server.protocol.ExternalProject);
         const project = service.configuredProjects.get(config.path)!;
-        assert.equal(project.pendingReload, ts.ConfigFileProgramReloadLevel.Full); // External project referenced configured project pending to be reloaded
+        assert.equal(project.pendingUpdateLevel, ts.ProgramUpdateLevel.Full); // External project referenced configured project pending to be reloaded
 
         service.setHostConfiguration({ preferences: { lazyConfiguredProjectsFromExternalProject: false } });
-        assert.equal(project.pendingReload, ts.ConfigFileProgramReloadLevel.None); // External project referenced configured project loaded
+        assert.equal(project.pendingUpdateLevel, ts.ProgramUpdateLevel.Update); // External project referenced configured project loaded
 
         service.closeExternalProject(projectFileName);
 
@@ -698,7 +698,7 @@ describe("unittests:: tsserver:: externalProjects", () => {
             options: {},
         } as ts.server.protocol.ExternalProject);
         const project2 = service.configuredProjects.get(config.path)!;
-        assert.equal(project2.pendingReload, ts.ConfigFileProgramReloadLevel.None); // External project referenced configured project loaded
+        assert.equal(project2.pendingUpdateLevel, ts.ProgramUpdateLevel.Update); // External project referenced configured project loaded
         baselineTsserverLogs("externalProjects", "handles loads existing configured projects of external projects when lazyConfiguredProjectsFromExternalProject is disabled", service);
     });
 
diff --git a/src/testRunner/unittests/tsserver/plugins.ts b/src/testRunner/unittests/tsserver/plugins.ts
index bcc1add3b9706..c73f12b987d76 100644
--- a/src/testRunner/unittests/tsserver/plugins.ts
+++ b/src/testRunner/unittests/tsserver/plugins.ts
@@ -225,6 +225,10 @@ describe("unittests:: tsserver:: plugins:: supportedExtensions::", () => {
             path: "/user/username/projects/myproject/a.ts",
             content: `export const a = 10;`,
         };
+        const dTs: File = {
+            path: "/user/username/projects/myproject/d.ts",
+            content: `export const d = 10;`,
+        };
         const bVue: File = {
             path: "/user/username/projects/myproject/b.vue",
             content: "bVue file",
@@ -240,7 +244,8 @@ describe("unittests:: tsserver:: plugins:: supportedExtensions::", () => {
                 " ",
             ),
         };
-        const host = createServerHost([aTs, bVue, config, libFile]);
+        const host = createServerHost([aTs, dTs, bVue, config, libFile]);
+        const externalFiles = new Map<ts.server.Project, string[]>();
         host.require = () => {
             return {
                 module: () => ({
@@ -258,8 +263,16 @@ describe("unittests:: tsserver:: plugins:: supportedExtensions::", () => {
                                 originalGetScriptSnapshot(fileName);
                         return proxy;
                     },
-                    getExternalFiles: (project: ts.server.Project) => {
+                    getExternalFiles: (project: ts.server.Project, updateLevel: ts.ProgramUpdateLevel) => {
                         if (project.projectKind !== ts.server.ProjectKind.Configured) return [];
+                        if (updateLevel === ts.ProgramUpdateLevel.Update) {
+                            const existing = externalFiles.get(project);
+                            if (existing) {
+                                session.logger.log(`getExternalFiles:: Returning cached .vue files`);
+                                return existing;
+                            }
+                        }
+                        session.logger.log(`getExternalFiles:: Getting new list of .vue files`);
                         const configFile = project.getProjectName();
                         const config = ts.readJsonConfigFile(configFile, project.readFile.bind(project));
                         const parseHost: ts.ParseConfigHost = {
@@ -272,6 +285,7 @@ describe("unittests:: tsserver:: plugins:: supportedExtensions::", () => {
                             },
                         };
                         const parsed = ts.parseJsonSourceFileConfigFileContent(config, parseHost, project.getCurrentDirectory());
+                        externalFiles.set(project, parsed.fileNames);
                         return parsed.fileNames;
                     },
                 }),
@@ -284,6 +298,9 @@ describe("unittests:: tsserver:: plugins:: supportedExtensions::", () => {
         host.writeFile("/user/username/projects/myproject/c.vue", "cVue file");
         host.runQueuedTimeoutCallbacks();
 
+        host.appendFile(dTs.path, "export const x = 10;");
+        host.runQueuedTimeoutCallbacks();
+
         baselineTsserverLogs("plugins", "new files with non ts extensions with wildcard matching", session);
     });
 });
diff --git a/tests/baselines/reference/api/typescript.d.ts b/tests/baselines/reference/api/typescript.d.ts
index 00e41bf46de3f..4b783a4b8dca4 100644
--- a/tests/baselines/reference/api/typescript.d.ts
+++ b/tests/baselines/reference/api/typescript.d.ts
@@ -3274,7 +3274,7 @@ declare namespace ts {
         }
         interface PluginModule {
             create(createInfo: PluginCreateInfo): LanguageService;
-            getExternalFiles?(proj: Project): string[];
+            getExternalFiles?(proj: Project, updateLevel: ProgramUpdateLevel): string[];
             onConfigurationChanged?(config: any): void;
         }
         interface PluginModuleWithName {
@@ -3379,7 +3379,7 @@ declare namespace ts {
             disableLanguageService(lastFileExceededProgramSize?: string): void;
             getProjectName(): string;
             protected removeLocalTypingsFromTypeAcquisition(newTypeAcquisition: TypeAcquisition): TypeAcquisition;
-            getExternalFiles(): SortedReadonlyArray<string>;
+            getExternalFiles(updateLevel?: ProgramUpdateLevel): SortedReadonlyArray<string>;
             getSourceFile(path: Path): ts.SourceFile | undefined;
             close(): void;
             private detachScriptInfoIfNotRoot;
@@ -9829,6 +9829,19 @@ declare namespace ts {
     function getTsBuildInfoEmitOutputFilePath(options: CompilerOptions): string | undefined;
     function getOutputFileNames(commandLine: ParsedCommandLine, inputFileName: string, ignoreCase: boolean): readonly string[];
     function createPrinter(printerOptions?: PrinterOptions, handlers?: PrintHandlers): Printer;
+    enum ProgramUpdateLevel {
+        /** Program is updated with same root file names and options */
+        Update = 0,
+        /** Loads program after updating root file names from the disk */
+        RootNamesAndUpdate = 1,
+        /**
+         * Loads program completely, including:
+         *  - re-reading contents of config file from disk
+         *  - calculating root file names for the program
+         *  - Updating the program
+         */
+        Full = 2,
+    }
     function findConfigFile(searchPath: string, fileExists: (fileName: string) => boolean, configName?: string): string | undefined;
     function resolveTripleslashReference(moduleName: string, containingFile: string): string;
     function createCompilerHost(options: CompilerOptions, setParentNodes?: boolean): CompilerHost;
diff --git a/tests/baselines/reference/tsserver/plugins/new-files-with-non-ts-extensions-with-wildcard-matching.js b/tests/baselines/reference/tsserver/plugins/new-files-with-non-ts-extensions-with-wildcard-matching.js
index d8ff142f2819c..891fc361e9f8d 100644
--- a/tests/baselines/reference/tsserver/plugins/new-files-with-non-ts-extensions-with-wildcard-matching.js
+++ b/tests/baselines/reference/tsserver/plugins/new-files-with-non-ts-extensions-with-wildcard-matching.js
@@ -4,6 +4,9 @@ Before request
 //// [/user/username/projects/myproject/a.ts]
 export const a = 10;
 
+//// [/user/username/projects/myproject/d.ts]
+export const d = 10;
+
 //// [/user/username/projects/myproject/b.vue]
 bVue file
 
@@ -47,7 +50,8 @@ Info seq  [hh:mm:ss:mss] Creating configuration project /user/username/projects/
 Info seq  [hh:mm:ss:mss] FileWatcher:: Added:: WatchInfo: /user/username/projects/myproject/tsconfig.json 2000 undefined Project: /user/username/projects/myproject/tsconfig.json WatchType: Config file
 Info seq  [hh:mm:ss:mss] Config: /user/username/projects/myproject/tsconfig.json : {
  "rootNames": [
-  "/user/username/projects/myproject/a.ts"
+  "/user/username/projects/myproject/a.ts",
+  "/user/username/projects/myproject/d.ts"
  ],
  "options": {
   "composite": true,
@@ -60,6 +64,8 @@ Info seq  [hh:mm:ss:mss] Loading global plugin myplugin
 Info seq  [hh:mm:ss:mss] Enabling plugin myplugin from candidate paths: /a/lib/tsc.js/../../..
 Info seq  [hh:mm:ss:mss] Loading myplugin from /a/lib/tsc.js/../../.. (resolved to /a/lib/tsc.js/../../../node_modules)
 Info seq  [hh:mm:ss:mss] Plugin validation succeeded
+getExternalFiles:: Getting new list of .vue files
+Info seq  [hh:mm:ss:mss] FileWatcher:: Added:: WatchInfo: /user/username/projects/myproject/d.ts 500 undefined WatchType: Closed Script info
 Info seq  [hh:mm:ss:mss] FileWatcher:: Added:: WatchInfo: /user/username/projects/myproject/b.vue 500 undefined WatchType: Closed Script info
 Info seq  [hh:mm:ss:mss] Starting updateGraphWorker: Project: /user/username/projects/myproject/tsconfig.json
 Info seq  [hh:mm:ss:mss] FileWatcher:: Added:: WatchInfo: /a/lib/lib.d.ts 500 undefined WatchType: Closed Script info
@@ -67,11 +73,13 @@ Info seq  [hh:mm:ss:mss] DirectoryWatcher:: Added:: WatchInfo: /user/username/pr
 Info seq  [hh:mm:ss:mss] Elapsed:: *ms DirectoryWatcher:: Added:: WatchInfo: /user/username/projects/myproject/node_modules/@types 1 undefined Project: /user/username/projects/myproject/tsconfig.json WatchType: Type roots
 Info seq  [hh:mm:ss:mss] DirectoryWatcher:: Added:: WatchInfo: /user/username/projects/node_modules/@types 1 undefined Project: /user/username/projects/myproject/tsconfig.json WatchType: Type roots
 Info seq  [hh:mm:ss:mss] Elapsed:: *ms DirectoryWatcher:: Added:: WatchInfo: /user/username/projects/node_modules/@types 1 undefined Project: /user/username/projects/myproject/tsconfig.json WatchType: Type roots
+getExternalFiles:: Returning cached .vue files
 Info seq  [hh:mm:ss:mss] Finishing updateGraphWorker: Project: /user/username/projects/myproject/tsconfig.json Version: 1 structureChanged: true structureIsReused:: Not Elapsed:: *ms
 Info seq  [hh:mm:ss:mss] Project '/user/username/projects/myproject/tsconfig.json' (Configured)
-Info seq  [hh:mm:ss:mss] 	Files (3)
+Info seq  [hh:mm:ss:mss] 	Files (4)
 	/a/lib/lib.d.ts Text-1 "/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }"
 	/user/username/projects/myproject/a.ts SVC-1-0 "export const a = 10;"
+	/user/username/projects/myproject/d.ts Text-1 "export const d = 10;"
 	/user/username/projects/myproject/b.vue Text-1 "export const y = \"bVue file\";"
 
 
@@ -79,6 +87,8 @@ Info seq  [hh:mm:ss:mss] 	Files (3)
 	  Default library for target 'es5'
 	a.ts
 	  Matched by include pattern '*.ts' in 'tsconfig.json'
+	d.ts
+	  Matched by include pattern '*.ts' in 'tsconfig.json'
 	b.vue
 	  Matched by include pattern '*.vue' in 'tsconfig.json'
 
@@ -86,7 +96,7 @@ Info seq  [hh:mm:ss:mss] -----------------------------------------------
 Info seq  [hh:mm:ss:mss] Search path: /user/username/projects/myproject
 Info seq  [hh:mm:ss:mss] For info: /user/username/projects/myproject/tsconfig.json :: No config files found.
 Info seq  [hh:mm:ss:mss] Project '/user/username/projects/myproject/tsconfig.json' (Configured)
-Info seq  [hh:mm:ss:mss] 	Files (3)
+Info seq  [hh:mm:ss:mss] 	Files (4)
 
 Info seq  [hh:mm:ss:mss] -----------------------------------------------
 Info seq  [hh:mm:ss:mss] Open files: 
@@ -111,6 +121,8 @@ FsWatches::
   {}
 /user/username/projects/myproject/b.vue: *new*
   {}
+/user/username/projects/myproject/d.ts: *new*
+  {}
 /user/username/projects/myproject/tsconfig.json: *new*
   {}
 
@@ -126,13 +138,16 @@ cVue file
 
 
 Info seq  [hh:mm:ss:mss] Running: /user/username/projects/myproject/tsconfig.json
+getExternalFiles:: Getting new list of .vue files
 Info seq  [hh:mm:ss:mss] FileWatcher:: Added:: WatchInfo: /user/username/projects/myproject/c.vue 500 undefined WatchType: Closed Script info
 Info seq  [hh:mm:ss:mss] Starting updateGraphWorker: Project: /user/username/projects/myproject/tsconfig.json
+getExternalFiles:: Returning cached .vue files
 Info seq  [hh:mm:ss:mss] Finishing updateGraphWorker: Project: /user/username/projects/myproject/tsconfig.json Version: 2 structureChanged: true structureIsReused:: Not Elapsed:: *ms
 Info seq  [hh:mm:ss:mss] Project '/user/username/projects/myproject/tsconfig.json' (Configured)
-Info seq  [hh:mm:ss:mss] 	Files (4)
+Info seq  [hh:mm:ss:mss] 	Files (5)
 	/a/lib/lib.d.ts Text-1 "/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }"
 	/user/username/projects/myproject/a.ts SVC-1-0 "export const a = 10;"
+	/user/username/projects/myproject/d.ts Text-1 "export const d = 10;"
 	/user/username/projects/myproject/b.vue Text-1 "export const y = \"bVue file\";"
 	/user/username/projects/myproject/c.vue Text-1 "export const y = \"cVue file\";"
 
@@ -141,6 +156,8 @@ Info seq  [hh:mm:ss:mss] 	Files (4)
 	  Default library for target 'es5'
 	a.ts
 	  Matched by include pattern '*.ts' in 'tsconfig.json'
+	d.ts
+	  Matched by include pattern '*.ts' in 'tsconfig.json'
 	b.vue
 	  Matched by include pattern '*.vue' in 'tsconfig.json'
 	c.vue
@@ -150,7 +167,7 @@ Info seq  [hh:mm:ss:mss] -----------------------------------------------
 Info seq  [hh:mm:ss:mss] Running: *ensureProjectForOpenFiles*
 Info seq  [hh:mm:ss:mss] Before ensureProjectForOpenFiles:
 Info seq  [hh:mm:ss:mss] Project '/user/username/projects/myproject/tsconfig.json' (Configured)
-Info seq  [hh:mm:ss:mss] 	Files (4)
+Info seq  [hh:mm:ss:mss] 	Files (5)
 
 Info seq  [hh:mm:ss:mss] -----------------------------------------------
 Info seq  [hh:mm:ss:mss] Open files: 
@@ -158,7 +175,7 @@ Info seq  [hh:mm:ss:mss] 	FileName: /user/username/projects/myproject/a.ts Proje
 Info seq  [hh:mm:ss:mss] 		Projects: /user/username/projects/myproject/tsconfig.json
 Info seq  [hh:mm:ss:mss] After ensureProjectForOpenFiles:
 Info seq  [hh:mm:ss:mss] Project '/user/username/projects/myproject/tsconfig.json' (Configured)
-Info seq  [hh:mm:ss:mss] 	Files (4)
+Info seq  [hh:mm:ss:mss] 	Files (5)
 
 Info seq  [hh:mm:ss:mss] -----------------------------------------------
 Info seq  [hh:mm:ss:mss] Open files: 
@@ -181,5 +198,50 @@ FsWatches::
   {}
 /user/username/projects/myproject/c.vue: *new*
   {}
+/user/username/projects/myproject/d.ts:
+  {}
 /user/username/projects/myproject/tsconfig.json:
   {}
+
+Info seq  [hh:mm:ss:mss] FileWatcher:: Triggered with /user/username/projects/myproject/d.ts 1:: WatchInfo: /user/username/projects/myproject/d.ts 500 undefined WatchType: Closed Script info
+Info seq  [hh:mm:ss:mss] Scheduled: /user/username/projects/myproject/tsconfig.json
+Info seq  [hh:mm:ss:mss] Scheduled: *ensureProjectForOpenFiles*
+Info seq  [hh:mm:ss:mss] Elapsed:: *ms FileWatcher:: Triggered with /user/username/projects/myproject/d.ts 1:: WatchInfo: /user/username/projects/myproject/d.ts 500 undefined WatchType: Closed Script info
+Before running Timeout callback:: count: 2
+3: /user/username/projects/myproject/tsconfig.json
+4: *ensureProjectForOpenFiles*
+//// [/user/username/projects/myproject/d.ts]
+export const d = 10;export const x = 10;
+
+
+Info seq  [hh:mm:ss:mss] Running: /user/username/projects/myproject/tsconfig.json
+Info seq  [hh:mm:ss:mss] Starting updateGraphWorker: Project: /user/username/projects/myproject/tsconfig.json
+getExternalFiles:: Returning cached .vue files
+Info seq  [hh:mm:ss:mss] Finishing updateGraphWorker: Project: /user/username/projects/myproject/tsconfig.json Version: 3 structureChanged: false structureIsReused:: Completely Elapsed:: *ms
+Info seq  [hh:mm:ss:mss] Project '/user/username/projects/myproject/tsconfig.json' (Configured)
+Info seq  [hh:mm:ss:mss] 	Files (5)
+	/a/lib/lib.d.ts Text-1 "/// <reference no-default-lib=\"true\"/>\ninterface Boolean {}\ninterface Function {}\ninterface CallableFunction {}\ninterface NewableFunction {}\ninterface IArguments {}\ninterface Number { toExponential: any; }\ninterface Object {}\ninterface RegExp {}\ninterface String { charAt: any; }\ninterface Array<T> { length: number; [n: number]: T; }"
+	/user/username/projects/myproject/a.ts SVC-1-0 "export const a = 10;"
+	/user/username/projects/myproject/d.ts Text-2 "export const d = 10;export const x = 10;"
+	/user/username/projects/myproject/b.vue Text-1 "export const y = \"bVue file\";"
+	/user/username/projects/myproject/c.vue Text-1 "export const y = \"cVue file\";"
+
+Info seq  [hh:mm:ss:mss] -----------------------------------------------
+Info seq  [hh:mm:ss:mss] Running: *ensureProjectForOpenFiles*
+Info seq  [hh:mm:ss:mss] Before ensureProjectForOpenFiles:
+Info seq  [hh:mm:ss:mss] Project '/user/username/projects/myproject/tsconfig.json' (Configured)
+Info seq  [hh:mm:ss:mss] 	Files (5)
+
+Info seq  [hh:mm:ss:mss] -----------------------------------------------
+Info seq  [hh:mm:ss:mss] Open files: 
+Info seq  [hh:mm:ss:mss] 	FileName: /user/username/projects/myproject/a.ts ProjectRootPath: undefined
+Info seq  [hh:mm:ss:mss] 		Projects: /user/username/projects/myproject/tsconfig.json
+Info seq  [hh:mm:ss:mss] After ensureProjectForOpenFiles:
+Info seq  [hh:mm:ss:mss] Project '/user/username/projects/myproject/tsconfig.json' (Configured)
+Info seq  [hh:mm:ss:mss] 	Files (5)
+
+Info seq  [hh:mm:ss:mss] -----------------------------------------------
+Info seq  [hh:mm:ss:mss] Open files: 
+Info seq  [hh:mm:ss:mss] 	FileName: /user/username/projects/myproject/a.ts ProjectRootPath: undefined
+Info seq  [hh:mm:ss:mss] 		Projects: /user/username/projects/myproject/tsconfig.json
+After running Timeout callback:: count: 0

From 08d6df0813e9a2227afb26721e1f64ef0a402f6e Mon Sep 17 00:00:00 2001
From: TypeScript Bot <typescriptbot@microsoft.com>
Date: Tue, 10 Oct 2023 06:19:41 +0000
Subject: [PATCH 7/7] Update package-lock.json

---
 package-lock.json | 214 +++++++++++++++++++++++++---------------------
 1 file changed, 116 insertions(+), 98 deletions(-)

diff --git a/package-lock.json b/package-lock.json
index facac0374d15e..decca6968368a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -880,9 +880,9 @@
             }
         },
         "node_modules/@types/chai": {
-            "version": "4.3.6",
-            "resolved": "https://registry.npmjs.org/@types/chai/-/chai-4.3.6.tgz",
-            "integrity": "sha512-VOVRLM1mBxIRxydiViqPcKn6MIxZytrbMpd6RJLIWKxUNr3zux8no0Oc7kJx0WAPIitgZ0gkrDS+btlqQpubpw==",
+            "version": "4.3.7",
+            "resolved": "https://registry.npmjs.org/@types/chai/-/chai-4.3.7.tgz",
+            "integrity": "sha512-/k+vesl92vMvMygmQrFe9Aimxi6oQXFUX9mA5HanTrKUSAMoLauSi6PNFOdRw0oeqilaW600GNx2vSaT2f8aIQ==",
             "dev": true
         },
         "node_modules/@types/glob": {
@@ -938,10 +938,13 @@
             "dev": true
         },
         "node_modules/@types/node": {
-            "version": "20.8.3",
-            "resolved": "https://registry.npmjs.org/@types/node/-/node-20.8.3.tgz",
-            "integrity": "sha512-jxiZQFpb+NlH5kjW49vXxvxTjeeqlbsnTAdBTKpzEdPs9itay7MscYXz3Fo9VYFEsfQ6LJFitHad3faerLAjCw==",
-            "dev": true
+            "version": "20.8.4",
+            "resolved": "https://registry.npmjs.org/@types/node/-/node-20.8.4.tgz",
+            "integrity": "sha512-ZVPnqU58giiCjSxjVUESDtdPk4QR5WQhhINbc9UBrKLU68MX5BF6kbQzTrkwbolyr0X8ChBpXfavr5mZFKZQ5A==",
+            "dev": true,
+            "dependencies": {
+                "undici-types": "~5.25.1"
+            }
         },
         "node_modules/@types/semver": {
             "version": "7.5.3",
@@ -965,16 +968,16 @@
             "dev": true
         },
         "node_modules/@typescript-eslint/eslint-plugin": {
-            "version": "6.7.4",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/eslint-plugin/-/eslint-plugin-6.7.4.tgz",
-            "integrity": "sha512-DAbgDXwtX+pDkAHwiGhqP3zWUGpW49B7eqmgpPtg+BKJXwdct79ut9+ifqOFPJGClGKSHXn2PTBatCnldJRUoA==",
+            "version": "6.7.5",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/eslint-plugin/-/eslint-plugin-6.7.5.tgz",
+            "integrity": "sha512-JhtAwTRhOUcP96D0Y6KYnwig/MRQbOoLGXTON2+LlyB/N35SP9j1boai2zzwXb7ypKELXMx3DVk9UTaEq1vHEw==",
             "dev": true,
             "dependencies": {
                 "@eslint-community/regexpp": "^4.5.1",
-                "@typescript-eslint/scope-manager": "6.7.4",
-                "@typescript-eslint/type-utils": "6.7.4",
-                "@typescript-eslint/utils": "6.7.4",
-                "@typescript-eslint/visitor-keys": "6.7.4",
+                "@typescript-eslint/scope-manager": "6.7.5",
+                "@typescript-eslint/type-utils": "6.7.5",
+                "@typescript-eslint/utils": "6.7.5",
+                "@typescript-eslint/visitor-keys": "6.7.5",
                 "debug": "^4.3.4",
                 "graphemer": "^1.4.0",
                 "ignore": "^5.2.4",
@@ -1000,15 +1003,15 @@
             }
         },
         "node_modules/@typescript-eslint/parser": {
-            "version": "6.7.4",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/parser/-/parser-6.7.4.tgz",
-            "integrity": "sha512-I5zVZFY+cw4IMZUeNCU7Sh2PO5O57F7Lr0uyhgCJmhN/BuTlnc55KxPonR4+EM3GBdfiCyGZye6DgMjtubQkmA==",
+            "version": "6.7.5",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/parser/-/parser-6.7.5.tgz",
+            "integrity": "sha512-bIZVSGx2UME/lmhLcjdVc7ePBwn7CLqKarUBL4me1C5feOd663liTGjMBGVcGr+BhnSLeP4SgwdvNnnkbIdkCw==",
             "dev": true,
             "dependencies": {
-                "@typescript-eslint/scope-manager": "6.7.4",
-                "@typescript-eslint/types": "6.7.4",
-                "@typescript-eslint/typescript-estree": "6.7.4",
-                "@typescript-eslint/visitor-keys": "6.7.4",
+                "@typescript-eslint/scope-manager": "6.7.5",
+                "@typescript-eslint/types": "6.7.5",
+                "@typescript-eslint/typescript-estree": "6.7.5",
+                "@typescript-eslint/visitor-keys": "6.7.5",
                 "debug": "^4.3.4"
             },
             "engines": {
@@ -1028,13 +1031,13 @@
             }
         },
         "node_modules/@typescript-eslint/scope-manager": {
-            "version": "6.7.4",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/scope-manager/-/scope-manager-6.7.4.tgz",
-            "integrity": "sha512-SdGqSLUPTXAXi7c3Ob7peAGVnmMoGzZ361VswK2Mqf8UOYcODiYvs8rs5ILqEdfvX1lE7wEZbLyELCW+Yrql1A==",
+            "version": "6.7.5",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/scope-manager/-/scope-manager-6.7.5.tgz",
+            "integrity": "sha512-GAlk3eQIwWOJeb9F7MKQ6Jbah/vx1zETSDw8likab/eFcqkjSD7BI75SDAeC5N2L0MmConMoPvTsmkrg71+B1A==",
             "dev": true,
             "dependencies": {
-                "@typescript-eslint/types": "6.7.4",
-                "@typescript-eslint/visitor-keys": "6.7.4"
+                "@typescript-eslint/types": "6.7.5",
+                "@typescript-eslint/visitor-keys": "6.7.5"
             },
             "engines": {
                 "node": "^16.0.0 || >=18.0.0"
@@ -1045,13 +1048,13 @@
             }
         },
         "node_modules/@typescript-eslint/type-utils": {
-            "version": "6.7.4",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/type-utils/-/type-utils-6.7.4.tgz",
-            "integrity": "sha512-n+g3zi1QzpcAdHFP9KQF+rEFxMb2KxtnJGID3teA/nxKHOVi3ylKovaqEzGBbVY2pBttU6z85gp0D00ufLzViQ==",
+            "version": "6.7.5",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/type-utils/-/type-utils-6.7.5.tgz",
+            "integrity": "sha512-Gs0qos5wqxnQrvpYv+pf3XfcRXW6jiAn9zE/K+DlmYf6FcpxeNYN0AIETaPR7rHO4K2UY+D0CIbDP9Ut0U4m1g==",
             "dev": true,
             "dependencies": {
-                "@typescript-eslint/typescript-estree": "6.7.4",
-                "@typescript-eslint/utils": "6.7.4",
+                "@typescript-eslint/typescript-estree": "6.7.5",
+                "@typescript-eslint/utils": "6.7.5",
                 "debug": "^4.3.4",
                 "ts-api-utils": "^1.0.1"
             },
@@ -1072,9 +1075,9 @@
             }
         },
         "node_modules/@typescript-eslint/types": {
-            "version": "6.7.4",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/types/-/types-6.7.4.tgz",
-            "integrity": "sha512-o9XWK2FLW6eSS/0r/tgjAGsYasLAnOWg7hvZ/dGYSSNjCh+49k5ocPN8OmG5aZcSJ8pclSOyVKP2x03Sj+RrCA==",
+            "version": "6.7.5",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/types/-/types-6.7.5.tgz",
+            "integrity": "sha512-WboQBlOXtdj1tDFPyIthpKrUb+kZf2VroLZhxKa/VlwLlLyqv/PwUNgL30BlTVZV1Wu4Asu2mMYPqarSO4L5ZQ==",
             "dev": true,
             "engines": {
                 "node": "^16.0.0 || >=18.0.0"
@@ -1085,13 +1088,13 @@
             }
         },
         "node_modules/@typescript-eslint/typescript-estree": {
-            "version": "6.7.4",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-6.7.4.tgz",
-            "integrity": "sha512-ty8b5qHKatlNYd9vmpHooQz3Vki3gG+3PchmtsA4TgrZBKWHNjWfkQid7K7xQogBqqc7/BhGazxMD5vr6Ha+iQ==",
+            "version": "6.7.5",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/typescript-estree/-/typescript-estree-6.7.5.tgz",
+            "integrity": "sha512-NhJiJ4KdtwBIxrKl0BqG1Ur+uw7FiOnOThcYx9DpOGJ/Abc9z2xNzLeirCG02Ig3vkvrc2qFLmYSSsaITbKjlg==",
             "dev": true,
             "dependencies": {
-                "@typescript-eslint/types": "6.7.4",
-                "@typescript-eslint/visitor-keys": "6.7.4",
+                "@typescript-eslint/types": "6.7.5",
+                "@typescript-eslint/visitor-keys": "6.7.5",
                 "debug": "^4.3.4",
                 "globby": "^11.1.0",
                 "is-glob": "^4.0.3",
@@ -1112,17 +1115,17 @@
             }
         },
         "node_modules/@typescript-eslint/utils": {
-            "version": "6.7.4",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/utils/-/utils-6.7.4.tgz",
-            "integrity": "sha512-PRQAs+HUn85Qdk+khAxsVV+oULy3VkbH3hQ8hxLRJXWBEd7iI+GbQxH5SEUSH7kbEoTp6oT1bOwyga24ELALTA==",
+            "version": "6.7.5",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/utils/-/utils-6.7.5.tgz",
+            "integrity": "sha512-pfRRrH20thJbzPPlPc4j0UNGvH1PjPlhlCMq4Yx7EGjV7lvEeGX0U6MJYe8+SyFutWgSHsdbJ3BXzZccYggezA==",
             "dev": true,
             "dependencies": {
                 "@eslint-community/eslint-utils": "^4.4.0",
                 "@types/json-schema": "^7.0.12",
                 "@types/semver": "^7.5.0",
-                "@typescript-eslint/scope-manager": "6.7.4",
-                "@typescript-eslint/types": "6.7.4",
-                "@typescript-eslint/typescript-estree": "6.7.4",
+                "@typescript-eslint/scope-manager": "6.7.5",
+                "@typescript-eslint/types": "6.7.5",
+                "@typescript-eslint/typescript-estree": "6.7.5",
                 "semver": "^7.5.4"
             },
             "engines": {
@@ -1137,12 +1140,12 @@
             }
         },
         "node_modules/@typescript-eslint/visitor-keys": {
-            "version": "6.7.4",
-            "resolved": "https://registry.npmjs.org/@typescript-eslint/visitor-keys/-/visitor-keys-6.7.4.tgz",
-            "integrity": "sha512-pOW37DUhlTZbvph50x5zZCkFn3xzwkGtNoJHzIM3svpiSkJzwOYr/kVBaXmf+RAQiUDs1AHEZVNPg6UJCJpwRA==",
+            "version": "6.7.5",
+            "resolved": "https://registry.npmjs.org/@typescript-eslint/visitor-keys/-/visitor-keys-6.7.5.tgz",
+            "integrity": "sha512-3MaWdDZtLlsexZzDSdQWsFQ9l9nL8B80Z4fImSpyllFC/KLqWQRdEcB+gGGO+N3Q2uL40EsG66wZLsohPxNXvg==",
             "dev": true,
             "dependencies": {
-                "@typescript-eslint/types": "6.7.4",
+                "@typescript-eslint/types": "6.7.5",
                 "eslint-visitor-keys": "^3.4.1"
             },
             "engines": {
@@ -3729,6 +3732,12 @@
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