Merge pull request #10883 from Microsoft/fix10876

Fix missing final label

Author: rbuckton

src/compiler/transformers/generators.ts

@@ -2629,7 +2629,7 @@ namespace ts {
          * Flush the final label of the generator function body.
          */
         function flushFinalLabel(operationIndex: number): void {
-            if (!lastOperationWasCompletion) {
+            if (isFinalLabelReachable(operationIndex)) {
                 tryEnterLabel(operationIndex);
                 withBlockStack = undefined;
                 writeReturn(/*expression*/ undefined, /*operationLocation*/ undefined);
@@ -2642,6 +2642,34 @@ namespace ts {
             updateLabelExpressions();
         }
 
+        /**
+         * Tests whether the final label of the generator function body
+         * is reachable by user code.
+         */
+        function isFinalLabelReachable(operationIndex: number) {
+            // if the last operation was *not* a completion (return/throw) then
+            // the final label is reachable.
+            if (!lastOperationWasCompletion) {
+                return true;
+            }
+
+            // if there are no labels defined or referenced, then the final label is
+            // not reachable.
+            if (!labelOffsets || !labelExpressions) {
+                return false;
+            }
+
+            // if the label for this offset is referenced, then the final label
+            // is reachable.
+            for (let label = 0; label < labelOffsets.length; label++) {
+                if (labelOffsets[label] === operationIndex && labelExpressions[label]) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
         /**
          * Appends a case clause for the last label and sets the new label.
          *

tests/baselines/reference/generatorTransformFinalLabel.js

@@ -0,0 +1,28 @@
+//// [generatorTransformFinalLabel.ts]
+async function test(skip: boolean) {
+    if (!skip) {
+        await 1
+    }
+    else {
+        throw Error('test')
+    }
+}
+
+//// [generatorTransformFinalLabel.js]
+function test(skip) {
+    return __awaiter(this, void 0, void 0, function () {
+        return __generator(this, function (_a) {
+            switch (_a.label) {
+                case 0:
+                    if (!!skip)
+                        return [3 /*break*/, 2];
+                    return [4 /*yield*/, 1];
+                case 1:
+                    _a.sent();
+                    return [3 /*break*/, 3];
+                case 2: throw Error('test');
+                case 3: return [2 /*return*/];
+            }
+        });
+    });
+}

tests/baselines/reference/generatorTransformFinalLabel.symbols

@@ -0,0 +1,15 @@
+=== tests/cases/compiler/generatorTransformFinalLabel.ts ===
+async function test(skip: boolean) {
+>test : Symbol(test, Decl(generatorTransformFinalLabel.ts, 0, 0))
+>skip : Symbol(skip, Decl(generatorTransformFinalLabel.ts, 0, 20))
+
+    if (!skip) {
+>skip : Symbol(skip, Decl(generatorTransformFinalLabel.ts, 0, 20))
+
+        await 1
+    }
+    else {
+        throw Error('test')
+>Error : Symbol(Error, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+    }
+}

tests/baselines/reference/generatorTransformFinalLabel.types

@@ -0,0 +1,20 @@
+=== tests/cases/compiler/generatorTransformFinalLabel.ts ===
+async function test(skip: boolean) {
+>test : (skip: boolean) => Promise<void>
+>skip : boolean
+
+    if (!skip) {
+>!skip : boolean
+>skip : boolean
+
+        await 1
+>await 1 : 1
+>1 : 1
+    }
+    else {
+        throw Error('test')
+>Error('test') : Error
+>Error : ErrorConstructor
+>'test' : "test"
+    }
+}

tests/cases/compiler/generatorTransformFinalLabel.ts

@@ -0,0 +1,11 @@
+// @target: es5
+// @lib: es5,es6
+// @noEmitHelpers: true
+async function test(skip: boolean) {
+    if (!skip) {
+        await 1
+    }
+    else {
+        throw Error('test')
+    }
+}