Ban annotating function type with lifetime dependence

Author: meg-gupta

include/swift/AST/DiagnosticsSema.def

@@ -7994,6 +7994,9 @@ ERROR(lifetime_dependence_cannot_infer_ambiguous_candidate, none,
        ())
 ERROR(lifetime_dependence_immortal_conflict_name, none,
       "conflict between the parameter name and immortal keyword", ())
+ERROR(lifetime_dependence_function_type, none,
+      "lifetime dependencies on function types are not supported",
+      ())
 
 //===----------------------------------------------------------------------===//
 //                             MARK: Sending

lib/Sema/TypeCheckType.cpp

@@ -3961,6 +3961,12 @@ NeverNullType TypeResolver::resolveASTFunctionType(
     }
   }
 
+  if (auto *lifetimeRepr = dyn_cast_or_null<LifetimeDependentReturnTypeRepr>(
+          repr->getResultTypeRepr())) {
+    diagnoseInvalid(lifetimeRepr, lifetimeRepr->getLoc(),
+                    diag::lifetime_dependence_function_type);
+  }
+
   auto resultOptions = options.withoutContext();
   resultOptions.setContext(TypeResolverContext::FunctionResult);
   auto outputTy = resolveType(repr->getResultTypeRepr(), resultOptions);