Don't consult JSDoc outside of JS in expando function assignment declarations

src/compiler/checker.ts

@@ -10519,7 +10519,7 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
         // function/class/{} initializers are themselves containers, so they won't merge in the same way as other initializers
         const container = getAssignedExpandoInitializer(symbol.valueDeclaration);
         if (container) {
-            const tag = getJSDocTypeTag(container);
+            const tag = isInJSFile(container) ? getJSDocTypeTag(container) : undefined;
             if (tag && tag.typeExpression) {
                 return getTypeFromTypeNode(tag.typeExpression);
             }

tests/baselines/reference/expandoFunctionContextualTypesJSDocInTs.js

@@ -0,0 +1,17 @@
+//// [expandoFunctionContextualTypesJSDocInTs.ts]
+export function Foo() { }
+
+// This comment should have no effect; this is a TS file.
+/** @type {never} */
+Foo.bar = () => { };
+
+
+//// [expandoFunctionContextualTypesJSDocInTs.js]
+"use strict";
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.Foo = void 0;
+function Foo() { }
+exports.Foo = Foo;
+// This comment should have no effect; this is a TS file.
+/** @type {never} */
+Foo.bar = function () { };

tests/baselines/reference/expandoFunctionContextualTypesJSDocInTs.symbols

@@ -0,0 +1,11 @@
+=== tests/cases/compiler/expandoFunctionContextualTypesJSDocInTs.ts ===
+export function Foo() { }
+>Foo : Symbol(Foo, Decl(expandoFunctionContextualTypesJSDocInTs.ts, 0, 0), Decl(expandoFunctionContextualTypesJSDocInTs.ts, 0, 25))
+
+// This comment should have no effect; this is a TS file.
+/** @type {never} */
+Foo.bar = () => { };
+>Foo.bar : Symbol(Foo.bar, Decl(expandoFunctionContextualTypesJSDocInTs.ts, 0, 25))
+>Foo : Symbol(Foo, Decl(expandoFunctionContextualTypesJSDocInTs.ts, 0, 0), Decl(expandoFunctionContextualTypesJSDocInTs.ts, 0, 25))
+>bar : Symbol(Foo.bar, Decl(expandoFunctionContextualTypesJSDocInTs.ts, 0, 25))
+

tests/baselines/reference/expandoFunctionContextualTypesJSDocInTs.types

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/expandoFunctionContextualTypesJSDocInTs.ts ===
+export function Foo() { }
+>Foo : typeof Foo
+
+// This comment should have no effect; this is a TS file.
+/** @type {never} */
+Foo.bar = () => { };
+>Foo.bar = () => { } : () => void
+>Foo.bar : () => void
+>Foo : typeof Foo
+>bar : () => void
+>() => { } : () => void
+

tests/cases/compiler/expandoFunctionContextualTypesJSDocInTs.ts

@@ -0,0 +1,5 @@
+export function Foo() { }
+
+// This comment should have no effect; this is a TS file.
+/** @type {never} */
+Foo.bar = () => { };