From 3a439401f75f8634b75aede2db8c8cb44bce9721 Mon Sep 17 00:00:00 2001
From: Wesley Wigham <wewigham@microsoft.com>
Date: Wed, 14 Aug 2024 13:08:22 -0700
Subject: [PATCH] Expand intersection reduction division strategy down to
 3-member intersections (#59425)

---
 src/compiler/checker.ts                       |   4 +-
 .../reference/pickOfLargeObjectUnionWorks.js  |  85 ++++++
 .../pickOfLargeObjectUnionWorks.symbols       | 226 ++++++++++++++
 .../pickOfLargeObjectUnionWorks.types         | 275 ++++++++++++++++++
 .../compiler/pickOfLargeObjectUnionWorks.ts   |  79 +++++
 5 files changed, 667 insertions(+), 2 deletions(-)
 create mode 100644 tests/baselines/reference/pickOfLargeObjectUnionWorks.js
 create mode 100644 tests/baselines/reference/pickOfLargeObjectUnionWorks.symbols
 create mode 100644 tests/baselines/reference/pickOfLargeObjectUnionWorks.types
 create mode 100644 tests/cases/compiler/pickOfLargeObjectUnionWorks.ts

diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index a5bcfbd4fa976..1673c6c032716 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -18188,8 +18188,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
                     removeFromEach(typeSet, TypeFlags.Null);
                     result = getUnionType([getIntersectionType(typeSet, flags), nullType], UnionReduction.Literal, aliasSymbol, aliasTypeArguments);
                 }
-                else if (typeSet.length >= 4) {
-                    // When we have four or more constituents, some of which are unions, we employ a "divide and conquer" strategy
+                else if (typeSet.length >= 3 && types.length > 2) {
+                    // When we have three or more constituents, more than two inputs (to head off infinite reexpansion), some of which are unions, we employ a "divide and conquer" strategy
                     // where A & B & C & D is processed as (A & B) & (C & D). Since intersections of unions often produce far smaller
                     // unions of intersections than the full cartesian product (due to some intersections becoming `never`), this can
                     // dramatically reduce the overall work.
diff --git a/tests/baselines/reference/pickOfLargeObjectUnionWorks.js b/tests/baselines/reference/pickOfLargeObjectUnionWorks.js
new file mode 100644
index 0000000000000..fbe9db615a0e7
--- /dev/null
+++ b/tests/baselines/reference/pickOfLargeObjectUnionWorks.js
@@ -0,0 +1,85 @@
+//// [tests/cases/compiler/pickOfLargeObjectUnionWorks.ts] ////
+
+//// [pickOfLargeObjectUnionWorks.ts]
+interface HTMLDataAttributes {
+    [data: `data-${string}`]: unknown
+}
+
+interface Base {
+    id: string;
+    prop01: string;
+    prop02: string;
+    prop03: string;
+    prop04: string;
+    prop05: string;
+    prop06: string;
+    prop07: string;
+    prop08: string;
+    prop09: string;
+    prop10: string;
+    prop11: string;
+    prop12: string;
+    prop13: string;
+    prop14: string;
+    prop15: string;
+    prop16: string;
+    prop17: string;
+    prop18: string;
+    prop19: string;
+    prop20: string;
+    prop21: string;
+    prop22: string;
+    prop23: string;
+    prop24: string;
+    prop25: string;
+    prop26: string;
+    prop27: string;
+    prop28: string;
+    prop29: string;
+    prop30: string;
+    prop31: string;
+    prop32: string;
+    prop33: string;
+    prop34: string;
+    prop35: string;
+    prop36: string;
+    prop37: string;
+  }
+  
+  interface A extends Base, HTMLDataAttributes {
+    a1: string;
+    a2: string;
+    a3: string;
+    a4: string;
+    a5: string;
+    a6: string;
+    a7: string;
+    a8: string;
+  }
+  
+  interface B extends Base, HTMLDataAttributes {
+    b1: string;
+    b2: string;
+    b3: string;
+    b4: string;
+    b5: string;
+    b6: string;
+    b7: string;
+    b8: string;
+  }
+  
+  interface C extends Base, HTMLDataAttributes {
+    c1: string;
+    c2: string;
+    c3: string;
+    c4: string;
+    c5: string;
+    c6: string;
+    c7: string;
+    c8: string;
+  }
+  
+  const xyz: Pick<A | B | C, 'id'> = {id: 'id'}
+
+//// [pickOfLargeObjectUnionWorks.js]
+var xyz = { id: 'id' };
diff --git a/tests/baselines/reference/pickOfLargeObjectUnionWorks.symbols b/tests/baselines/reference/pickOfLargeObjectUnionWorks.symbols
new file mode 100644
index 0000000000000..dae25147b997b
--- /dev/null
+++ b/tests/baselines/reference/pickOfLargeObjectUnionWorks.symbols
@@ -0,0 +1,226 @@
+//// [tests/cases/compiler/pickOfLargeObjectUnionWorks.ts] ////
+
+=== pickOfLargeObjectUnionWorks.ts ===
+interface HTMLDataAttributes {
+>HTMLDataAttributes : Symbol(HTMLDataAttributes, Decl(pickOfLargeObjectUnionWorks.ts, 0, 0))
+
+    [data: `data-${string}`]: unknown
+>data : Symbol(data, Decl(pickOfLargeObjectUnionWorks.ts, 1, 5))
+}
+
+interface Base {
+>Base : Symbol(Base, Decl(pickOfLargeObjectUnionWorks.ts, 2, 1))
+
+    id: string;
+>id : Symbol(Base.id, Decl(pickOfLargeObjectUnionWorks.ts, 4, 16))
+
+    prop01: string;
+>prop01 : Symbol(Base.prop01, Decl(pickOfLargeObjectUnionWorks.ts, 5, 15))
+
+    prop02: string;
+>prop02 : Symbol(Base.prop02, Decl(pickOfLargeObjectUnionWorks.ts, 6, 19))
+
+    prop03: string;
+>prop03 : Symbol(Base.prop03, Decl(pickOfLargeObjectUnionWorks.ts, 7, 19))
+
+    prop04: string;
+>prop04 : Symbol(Base.prop04, Decl(pickOfLargeObjectUnionWorks.ts, 8, 19))
+
+    prop05: string;
+>prop05 : Symbol(Base.prop05, Decl(pickOfLargeObjectUnionWorks.ts, 9, 19))
+
+    prop06: string;
+>prop06 : Symbol(Base.prop06, Decl(pickOfLargeObjectUnionWorks.ts, 10, 19))
+
+    prop07: string;
+>prop07 : Symbol(Base.prop07, Decl(pickOfLargeObjectUnionWorks.ts, 11, 19))
+
+    prop08: string;
+>prop08 : Symbol(Base.prop08, Decl(pickOfLargeObjectUnionWorks.ts, 12, 19))
+
+    prop09: string;
+>prop09 : Symbol(Base.prop09, Decl(pickOfLargeObjectUnionWorks.ts, 13, 19))
+
+    prop10: string;
+>prop10 : Symbol(Base.prop10, Decl(pickOfLargeObjectUnionWorks.ts, 14, 19))
+
+    prop11: string;
+>prop11 : Symbol(Base.prop11, Decl(pickOfLargeObjectUnionWorks.ts, 15, 19))
+
+    prop12: string;
+>prop12 : Symbol(Base.prop12, Decl(pickOfLargeObjectUnionWorks.ts, 16, 19))
+
+    prop13: string;
+>prop13 : Symbol(Base.prop13, Decl(pickOfLargeObjectUnionWorks.ts, 17, 19))
+
+    prop14: string;
+>prop14 : Symbol(Base.prop14, Decl(pickOfLargeObjectUnionWorks.ts, 18, 19))
+
+    prop15: string;
+>prop15 : Symbol(Base.prop15, Decl(pickOfLargeObjectUnionWorks.ts, 19, 19))
+
+    prop16: string;
+>prop16 : Symbol(Base.prop16, Decl(pickOfLargeObjectUnionWorks.ts, 20, 19))
+
+    prop17: string;
+>prop17 : Symbol(Base.prop17, Decl(pickOfLargeObjectUnionWorks.ts, 21, 19))
+
+    prop18: string;
+>prop18 : Symbol(Base.prop18, Decl(pickOfLargeObjectUnionWorks.ts, 22, 19))
+
+    prop19: string;
+>prop19 : Symbol(Base.prop19, Decl(pickOfLargeObjectUnionWorks.ts, 23, 19))
+
+    prop20: string;
+>prop20 : Symbol(Base.prop20, Decl(pickOfLargeObjectUnionWorks.ts, 24, 19))
+
+    prop21: string;
+>prop21 : Symbol(Base.prop21, Decl(pickOfLargeObjectUnionWorks.ts, 25, 19))
+
+    prop22: string;
+>prop22 : Symbol(Base.prop22, Decl(pickOfLargeObjectUnionWorks.ts, 26, 19))
+
+    prop23: string;
+>prop23 : Symbol(Base.prop23, Decl(pickOfLargeObjectUnionWorks.ts, 27, 19))
+
+    prop24: string;
+>prop24 : Symbol(Base.prop24, Decl(pickOfLargeObjectUnionWorks.ts, 28, 19))
+
+    prop25: string;
+>prop25 : Symbol(Base.prop25, Decl(pickOfLargeObjectUnionWorks.ts, 29, 19))
+
+    prop26: string;
+>prop26 : Symbol(Base.prop26, Decl(pickOfLargeObjectUnionWorks.ts, 30, 19))
+
+    prop27: string;
+>prop27 : Symbol(Base.prop27, Decl(pickOfLargeObjectUnionWorks.ts, 31, 19))
+
+    prop28: string;
+>prop28 : Symbol(Base.prop28, Decl(pickOfLargeObjectUnionWorks.ts, 32, 19))
+
+    prop29: string;
+>prop29 : Symbol(Base.prop29, Decl(pickOfLargeObjectUnionWorks.ts, 33, 19))
+
+    prop30: string;
+>prop30 : Symbol(Base.prop30, Decl(pickOfLargeObjectUnionWorks.ts, 34, 19))
+
+    prop31: string;
+>prop31 : Symbol(Base.prop31, Decl(pickOfLargeObjectUnionWorks.ts, 35, 19))
+
+    prop32: string;
+>prop32 : Symbol(Base.prop32, Decl(pickOfLargeObjectUnionWorks.ts, 36, 19))
+
+    prop33: string;
+>prop33 : Symbol(Base.prop33, Decl(pickOfLargeObjectUnionWorks.ts, 37, 19))
+
+    prop34: string;
+>prop34 : Symbol(Base.prop34, Decl(pickOfLargeObjectUnionWorks.ts, 38, 19))
+
+    prop35: string;
+>prop35 : Symbol(Base.prop35, Decl(pickOfLargeObjectUnionWorks.ts, 39, 19))
+
+    prop36: string;
+>prop36 : Symbol(Base.prop36, Decl(pickOfLargeObjectUnionWorks.ts, 40, 19))
+
+    prop37: string;
+>prop37 : Symbol(Base.prop37, Decl(pickOfLargeObjectUnionWorks.ts, 41, 19))
+  }
+  
+  interface A extends Base, HTMLDataAttributes {
+>A : Symbol(A, Decl(pickOfLargeObjectUnionWorks.ts, 43, 3))
+>Base : Symbol(Base, Decl(pickOfLargeObjectUnionWorks.ts, 2, 1))
+>HTMLDataAttributes : Symbol(HTMLDataAttributes, Decl(pickOfLargeObjectUnionWorks.ts, 0, 0))
+
+    a1: string;
+>a1 : Symbol(A.a1, Decl(pickOfLargeObjectUnionWorks.ts, 45, 48))
+
+    a2: string;
+>a2 : Symbol(A.a2, Decl(pickOfLargeObjectUnionWorks.ts, 46, 15))
+
+    a3: string;
+>a3 : Symbol(A.a3, Decl(pickOfLargeObjectUnionWorks.ts, 47, 15))
+
+    a4: string;
+>a4 : Symbol(A.a4, Decl(pickOfLargeObjectUnionWorks.ts, 48, 15))
+
+    a5: string;
+>a5 : Symbol(A.a5, Decl(pickOfLargeObjectUnionWorks.ts, 49, 15))
+
+    a6: string;
+>a6 : Symbol(A.a6, Decl(pickOfLargeObjectUnionWorks.ts, 50, 15))
+
+    a7: string;
+>a7 : Symbol(A.a7, Decl(pickOfLargeObjectUnionWorks.ts, 51, 15))
+
+    a8: string;
+>a8 : Symbol(A.a8, Decl(pickOfLargeObjectUnionWorks.ts, 52, 15))
+  }
+  
+  interface B extends Base, HTMLDataAttributes {
+>B : Symbol(B, Decl(pickOfLargeObjectUnionWorks.ts, 54, 3))
+>Base : Symbol(Base, Decl(pickOfLargeObjectUnionWorks.ts, 2, 1))
+>HTMLDataAttributes : Symbol(HTMLDataAttributes, Decl(pickOfLargeObjectUnionWorks.ts, 0, 0))
+
+    b1: string;
+>b1 : Symbol(B.b1, Decl(pickOfLargeObjectUnionWorks.ts, 56, 48))
+
+    b2: string;
+>b2 : Symbol(B.b2, Decl(pickOfLargeObjectUnionWorks.ts, 57, 15))
+
+    b3: string;
+>b3 : Symbol(B.b3, Decl(pickOfLargeObjectUnionWorks.ts, 58, 15))
+
+    b4: string;
+>b4 : Symbol(B.b4, Decl(pickOfLargeObjectUnionWorks.ts, 59, 15))
+
+    b5: string;
+>b5 : Symbol(B.b5, Decl(pickOfLargeObjectUnionWorks.ts, 60, 15))
+
+    b6: string;
+>b6 : Symbol(B.b6, Decl(pickOfLargeObjectUnionWorks.ts, 61, 15))
+
+    b7: string;
+>b7 : Symbol(B.b7, Decl(pickOfLargeObjectUnionWorks.ts, 62, 15))
+
+    b8: string;
+>b8 : Symbol(B.b8, Decl(pickOfLargeObjectUnionWorks.ts, 63, 15))
+  }
+  
+  interface C extends Base, HTMLDataAttributes {
+>C : Symbol(C, Decl(pickOfLargeObjectUnionWorks.ts, 65, 3))
+>Base : Symbol(Base, Decl(pickOfLargeObjectUnionWorks.ts, 2, 1))
+>HTMLDataAttributes : Symbol(HTMLDataAttributes, Decl(pickOfLargeObjectUnionWorks.ts, 0, 0))
+
+    c1: string;
+>c1 : Symbol(C.c1, Decl(pickOfLargeObjectUnionWorks.ts, 67, 48))
+
+    c2: string;
+>c2 : Symbol(C.c2, Decl(pickOfLargeObjectUnionWorks.ts, 68, 15))
+
+    c3: string;
+>c3 : Symbol(C.c3, Decl(pickOfLargeObjectUnionWorks.ts, 69, 15))
+
+    c4: string;
+>c4 : Symbol(C.c4, Decl(pickOfLargeObjectUnionWorks.ts, 70, 15))
+
+    c5: string;
+>c5 : Symbol(C.c5, Decl(pickOfLargeObjectUnionWorks.ts, 71, 15))
+
+    c6: string;
+>c6 : Symbol(C.c6, Decl(pickOfLargeObjectUnionWorks.ts, 72, 15))
+
+    c7: string;
+>c7 : Symbol(C.c7, Decl(pickOfLargeObjectUnionWorks.ts, 73, 15))
+
+    c8: string;
+>c8 : Symbol(C.c8, Decl(pickOfLargeObjectUnionWorks.ts, 74, 15))
+  }
+  
+  const xyz: Pick<A | B | C, 'id'> = {id: 'id'}
+>xyz : Symbol(xyz, Decl(pickOfLargeObjectUnionWorks.ts, 78, 7))
+>Pick : Symbol(Pick, Decl(lib.es5.d.ts, --, --))
+>A : Symbol(A, Decl(pickOfLargeObjectUnionWorks.ts, 43, 3))
+>B : Symbol(B, Decl(pickOfLargeObjectUnionWorks.ts, 54, 3))
+>C : Symbol(C, Decl(pickOfLargeObjectUnionWorks.ts, 65, 3))
+>id : Symbol(id, Decl(pickOfLargeObjectUnionWorks.ts, 78, 38))
+
diff --git a/tests/baselines/reference/pickOfLargeObjectUnionWorks.types b/tests/baselines/reference/pickOfLargeObjectUnionWorks.types
new file mode 100644
index 0000000000000..3a637bd997b8f
--- /dev/null
+++ b/tests/baselines/reference/pickOfLargeObjectUnionWorks.types
@@ -0,0 +1,275 @@
+//// [tests/cases/compiler/pickOfLargeObjectUnionWorks.ts] ////
+
+=== pickOfLargeObjectUnionWorks.ts ===
+interface HTMLDataAttributes {
+    [data: `data-${string}`]: unknown
+>data : `data-${string}`
+>     : ^^^^^^^^^^^^^^^^
+}
+
+interface Base {
+    id: string;
+>id : string
+>   : ^^^^^^
+
+    prop01: string;
+>prop01 : string
+>       : ^^^^^^
+
+    prop02: string;
+>prop02 : string
+>       : ^^^^^^
+
+    prop03: string;
+>prop03 : string
+>       : ^^^^^^
+
+    prop04: string;
+>prop04 : string
+>       : ^^^^^^
+
+    prop05: string;
+>prop05 : string
+>       : ^^^^^^
+
+    prop06: string;
+>prop06 : string
+>       : ^^^^^^
+
+    prop07: string;
+>prop07 : string
+>       : ^^^^^^
+
+    prop08: string;
+>prop08 : string
+>       : ^^^^^^
+
+    prop09: string;
+>prop09 : string
+>       : ^^^^^^
+
+    prop10: string;
+>prop10 : string
+>       : ^^^^^^
+
+    prop11: string;
+>prop11 : string
+>       : ^^^^^^
+
+    prop12: string;
+>prop12 : string
+>       : ^^^^^^
+
+    prop13: string;
+>prop13 : string
+>       : ^^^^^^
+
+    prop14: string;
+>prop14 : string
+>       : ^^^^^^
+
+    prop15: string;
+>prop15 : string
+>       : ^^^^^^
+
+    prop16: string;
+>prop16 : string
+>       : ^^^^^^
+
+    prop17: string;
+>prop17 : string
+>       : ^^^^^^
+
+    prop18: string;
+>prop18 : string
+>       : ^^^^^^
+
+    prop19: string;
+>prop19 : string
+>       : ^^^^^^
+
+    prop20: string;
+>prop20 : string
+>       : ^^^^^^
+
+    prop21: string;
+>prop21 : string
+>       : ^^^^^^
+
+    prop22: string;
+>prop22 : string
+>       : ^^^^^^
+
+    prop23: string;
+>prop23 : string
+>       : ^^^^^^
+
+    prop24: string;
+>prop24 : string
+>       : ^^^^^^
+
+    prop25: string;
+>prop25 : string
+>       : ^^^^^^
+
+    prop26: string;
+>prop26 : string
+>       : ^^^^^^
+
+    prop27: string;
+>prop27 : string
+>       : ^^^^^^
+
+    prop28: string;
+>prop28 : string
+>       : ^^^^^^
+
+    prop29: string;
+>prop29 : string
+>       : ^^^^^^
+
+    prop30: string;
+>prop30 : string
+>       : ^^^^^^
+
+    prop31: string;
+>prop31 : string
+>       : ^^^^^^
+
+    prop32: string;
+>prop32 : string
+>       : ^^^^^^
+
+    prop33: string;
+>prop33 : string
+>       : ^^^^^^
+
+    prop34: string;
+>prop34 : string
+>       : ^^^^^^
+
+    prop35: string;
+>prop35 : string
+>       : ^^^^^^
+
+    prop36: string;
+>prop36 : string
+>       : ^^^^^^
+
+    prop37: string;
+>prop37 : string
+>       : ^^^^^^
+  }
+  
+  interface A extends Base, HTMLDataAttributes {
+    a1: string;
+>a1 : string
+>   : ^^^^^^
+
+    a2: string;
+>a2 : string
+>   : ^^^^^^
+
+    a3: string;
+>a3 : string
+>   : ^^^^^^
+
+    a4: string;
+>a4 : string
+>   : ^^^^^^
+
+    a5: string;
+>a5 : string
+>   : ^^^^^^
+
+    a6: string;
+>a6 : string
+>   : ^^^^^^
+
+    a7: string;
+>a7 : string
+>   : ^^^^^^
+
+    a8: string;
+>a8 : string
+>   : ^^^^^^
+  }
+  
+  interface B extends Base, HTMLDataAttributes {
+    b1: string;
+>b1 : string
+>   : ^^^^^^
+
+    b2: string;
+>b2 : string
+>   : ^^^^^^
+
+    b3: string;
+>b3 : string
+>   : ^^^^^^
+
+    b4: string;
+>b4 : string
+>   : ^^^^^^
+
+    b5: string;
+>b5 : string
+>   : ^^^^^^
+
+    b6: string;
+>b6 : string
+>   : ^^^^^^
+
+    b7: string;
+>b7 : string
+>   : ^^^^^^
+
+    b8: string;
+>b8 : string
+>   : ^^^^^^
+  }
+  
+  interface C extends Base, HTMLDataAttributes {
+    c1: string;
+>c1 : string
+>   : ^^^^^^
+
+    c2: string;
+>c2 : string
+>   : ^^^^^^
+
+    c3: string;
+>c3 : string
+>   : ^^^^^^
+
+    c4: string;
+>c4 : string
+>   : ^^^^^^
+
+    c5: string;
+>c5 : string
+>   : ^^^^^^
+
+    c6: string;
+>c6 : string
+>   : ^^^^^^
+
+    c7: string;
+>c7 : string
+>   : ^^^^^^
+
+    c8: string;
+>c8 : string
+>   : ^^^^^^
+  }
+  
+  const xyz: Pick<A | B | C, 'id'> = {id: 'id'}
+>xyz : Pick<A | B | C, "id">
+>    : ^^^^^^^^^^^^^^^^^^^^^
+>{id: 'id'} : { id: string; }
+>           : ^^^^^^^^^^^^^^^
+>id : string
+>   : ^^^^^^
+>'id' : "id"
+>     : ^^^^
+
diff --git a/tests/cases/compiler/pickOfLargeObjectUnionWorks.ts b/tests/cases/compiler/pickOfLargeObjectUnionWorks.ts
new file mode 100644
index 0000000000000..b416fac1ed680
--- /dev/null
+++ b/tests/cases/compiler/pickOfLargeObjectUnionWorks.ts
@@ -0,0 +1,79 @@
+interface HTMLDataAttributes {
+    [data: `data-${string}`]: unknown
+}
+
+interface Base {
+    id: string;
+    prop01: string;
+    prop02: string;
+    prop03: string;
+    prop04: string;
+    prop05: string;
+    prop06: string;
+    prop07: string;
+    prop08: string;
+    prop09: string;
+    prop10: string;
+    prop11: string;
+    prop12: string;
+    prop13: string;
+    prop14: string;
+    prop15: string;
+    prop16: string;
+    prop17: string;
+    prop18: string;
+    prop19: string;
+    prop20: string;
+    prop21: string;
+    prop22: string;
+    prop23: string;
+    prop24: string;
+    prop25: string;
+    prop26: string;
+    prop27: string;
+    prop28: string;
+    prop29: string;
+    prop30: string;
+    prop31: string;
+    prop32: string;
+    prop33: string;
+    prop34: string;
+    prop35: string;
+    prop36: string;
+    prop37: string;
+  }
+  
+  interface A extends Base, HTMLDataAttributes {
+    a1: string;
+    a2: string;
+    a3: string;
+    a4: string;
+    a5: string;
+    a6: string;
+    a7: string;
+    a8: string;
+  }
+  
+  interface B extends Base, HTMLDataAttributes {
+    b1: string;
+    b2: string;
+    b3: string;
+    b4: string;
+    b5: string;
+    b6: string;
+    b7: string;
+    b8: string;
+  }
+  
+  interface C extends Base, HTMLDataAttributes {
+    c1: string;
+    c2: string;
+    c3: string;
+    c4: string;
+    c5: string;
+    c6: string;
+    c7: string;
+    c8: string;
+  }
+  
+  const xyz: Pick<A | B | C, 'id'> = {id: 'id'}
\ No newline at end of file