Instantiate contextual type for return type in getReturnTypeFromBody

Author: ahejlsberg

src/compiler/checker.ts

@@ -19051,7 +19051,7 @@ namespace ts {
 
         // If the given contextual type contains instantiable types and if a mapper representing
         // return type inferences is available, instantiate those types using that mapper.
-        function instantiateContextualType(contextualType: Type | undefined, node: Expression, contextFlags?: ContextFlags): Type | undefined {
+        function instantiateContextualType(contextualType: Type | undefined, node: Node, contextFlags?: ContextFlags): Type | undefined {
             if (contextualType && maybeTypeOfKind(contextualType, TypeFlags.Instantiable)) {
                 const inferenceContext = getInferenceContext(node);
                 // If no inferences have been made, nothing is gained from instantiating as type parameters
@@ -23363,7 +23363,7 @@ namespace ts {
                     nextType && isUnitType(nextType)) {
                     const contextualType = !contextualSignature ? undefined :
                         contextualSignature === getSignatureFromDeclaration(func) ? isGenerator ? undefined : returnType :
-                        getReturnTypeOfSignature(contextualSignature);
+                        instantiateContextualType(getReturnTypeOfSignature(contextualSignature), func);
                     if (isGenerator) {
                         yieldType = getWidenedLiteralLikeTypeForContextualIterationTypeIfNeeded(yieldType, contextualType, IterationTypeKind.Yield, isAsync);
                         returnType = getWidenedLiteralLikeTypeForContextualIterationTypeIfNeeded(returnType, contextualType, IterationTypeKind.Return, isAsync);