fix for await transform when a label is present

CHANGELOG.md

@@ -1,5 +1,65 @@
 # Changelog
 
+## Unreleased
+
+* Fix `for await` transform when a label is present
+
+    This release fixes a bug where the `for await` transform, which wraps the loop in a `try` statement, previously failed to also move the loop's label into the `try` statement. This bug only affects code that uses both of these features in combination. Here's an example of some affected code:
+
+    ```js
+    // Original code
+    async function test() {
+      outer: for await (const x of [Promise.resolve([0, 1])]) {
+        for (const y of x) if (y) break outer
+        throw 'fail'
+      }
+    }
+
+    // Old output (with --target=es6)
+    function test() {
+      return __async(this, null, function* () {
+        outer: try {
+          for (var iter = __forAwait([Promise.resolve([0, 1])]), more, temp, error; more = !(temp = yield iter.next()).done; more = false) {
+            const x = temp.value;
+            for (const y of x) if (y) break outer;
+            throw "fail";
+          }
+        } catch (temp) {
+          error = [temp];
+        } finally {
+          try {
+            more && (temp = iter.return) && (yield temp.call(iter));
+          } finally {
+            if (error)
+              throw error[0];
+          }
+        }
+      });
+    }
+
+    // New output (with --target=es6)
+    function test() {
+      return __async(this, null, function* () {
+        try {
+          outer: for (var iter = __forAwait([Promise.resolve([0, 1])]), more, temp, error; more = !(temp = yield iter.next()).done; more = false) {
+            const x = temp.value;
+            for (const y of x) if (y) break outer;
+            throw "fail";
+          }
+        } catch (temp) {
+          error = [temp];
+        } finally {
+          try {
+            more && (temp = iter.return) && (yield temp.call(iter));
+          } finally {
+            if (error)
+              throw error[0];
+          }
+        }
+      });
+    }
+    ```
+
 ## 0.21.3
 
 * Implement the decorator metadata proposal ([#3760](https://github.com/evanw/esbuild/issues/3760))

internal/bundler_tests/bundler_lower_test.go

@@ -2337,6 +2337,8 @@ func TestLowerForAwait2017(t *testing.T) {
 					async () => { for await (x.y of y) z(x) },
 					async () => { for await (let x of y) z(x) },
 					async () => { for await (const x of y) z(x) },
+					async () => { label: for await (const x of y) break label },
+					async () => { label: for await (const x of y) continue label },
 				]
 			`,
 		},
@@ -2358,6 +2360,8 @@ func TestLowerForAwait2015(t *testing.T) {
 					async () => { for await (x.y of y) z(x) },
 					async () => { for await (let x of y) z(x) },
 					async () => { for await (const x of y) z(x) },
+					async () => { label: for await (const x of y) break label },
+					async () => { label: for await (const x of y) continue label },
 				]
 			`,
 		},

internal/bundler_tests/snapshots/snapshots_lower.txt

@@ -2060,6 +2060,40 @@ export default [
           throw error[0];
       }
     }
+  }),
+  () => __async(void 0, null, function* () {
+    try {
+      label: for (var iter = __forAwait(y), more, temp, error; more = !(temp = yield iter.next()).done; more = false) {
+        const x2 = temp.value;
+        break label;
+      }
+    } catch (temp) {
+      error = [temp];
+    } finally {
+      try {
+        more && (temp = iter.return) && (yield temp.call(iter));
+      } finally {
+        if (error)
+          throw error[0];
+      }
+    }
+  }),
+  () => __async(void 0, null, function* () {
+    try {
+      label: for (var iter = __forAwait(y), more, temp, error; more = !(temp = yield iter.next()).done; more = false) {
+        const x2 = temp.value;
+        continue label;
+      }
+    } catch (temp) {
+      error = [temp];
+    } finally {
+      try {
+        more && (temp = iter.return) && (yield temp.call(iter));
+      } finally {
+        if (error)
+          throw error[0];
+      }
+    }
   })
 ];
 
@@ -2134,6 +2168,40 @@ export default [
           throw error[0];
       }
     }
+  },
+  async () => {
+    try {
+      label: for (var iter = __forAwait(y), more, temp, error; more = !(temp = await iter.next()).done; more = false) {
+        const x2 = temp.value;
+        break label;
+      }
+    } catch (temp) {
+      error = [temp];
+    } finally {
+      try {
+        more && (temp = iter.return) && await temp.call(iter);
+      } finally {
+        if (error)
+          throw error[0];
+      }
+    }
+  },
+  async () => {
+    try {
+      label: for (var iter = __forAwait(y), more, temp, error; more = !(temp = await iter.next()).done; more = false) {
+        const x2 = temp.value;
+        continue label;
+      }
+    } catch (temp) {
+      error = [temp];
+    } finally {
+      try {
+        more && (temp = iter.return) && await temp.call(iter);
+      } finally {
+        if (error)
+          throw error[0];
+      }
+    }
   }
 ];
 

internal/js_parser/js_parser.go

@@ -10284,6 +10284,18 @@ func (p *parser) visitAndAppendStmt(stmts []js_ast.Stmt, stmt js_ast.Stmt) []js_
 			}
 		}
 
+		// Handle "for await" that has been lowered by moving this label inside the "try"
+		if try, ok := s.Stmt.Data.(*js_ast.STry); ok && len(try.Block.Stmts) > 0 {
+			if _, ok := try.Block.Stmts[0].Data.(*js_ast.SFor); ok {
+				try.Block.Stmts[0] = js_ast.Stmt{Loc: stmt.Loc, Data: &js_ast.SLabel{
+					Stmt:             try.Block.Stmts[0],
+					Name:             s.Name,
+					IsSingleLineStmt: s.IsSingleLineStmt,
+				}}
+				return append(stmts, s.Stmt)
+			}
+		}
+
 	case *js_ast.SLocal:
 		// Silently remove unsupported top-level "await" in dead code branches
 		if s.Kind == js_ast.LocalAwaitUsing && p.fnOrArrowDataVisit.isOutsideFnOrArrow {

scripts/end-to-end-tests.js

@@ -7149,6 +7149,23 @@ for (let flags of [[], ['--target=es2017'], ['--target=es6']]) {
         }
       `,
     }, { async: true }),
+
+    // https://github.com/arogozine/LinqToTypeScript/issues/29
+    test(['in.js', '--outfile=node.js'].concat(flags), {
+      'in.js': `
+        exports.async = async () => {
+          let total = 0
+        outer:
+          for await (const n of [Promise.resolve(1), Promise.resolve(2), Promise.resolve(5)]) {
+            for (let i = 1; i <= n; i++) {
+              if (i === 4) continue outer
+              total += i
+            }
+          }
+          if (total !== 1 + (1 + 2) + (1 + 2 + 3)) throw 'fail'
+        }
+      `,
+    }, { async: true }),
   )
 }