[Sema] Type checking forbids typed throw on @objc functions now

Signed-off-by: Peter Rong <PeterRong@meta.com>

Author: DataCorrupted

include/swift/AST/DiagnosticsSema.def

@@ -5461,6 +5461,9 @@ WARNING(no_throw_in_do_with_catch,none,
 ERROR(thrown_type_not_error,none,
       "thrown type %0 does not conform to the 'Error' protocol", (Type))
 
+ERROR(typed_thrown_in_objc_forbidden,none,
+      "typed throw can't be applied to @objc functions", ())
+
 //------------------------------------------------------------------------------
 // MARK: Concurrency
 //------------------------------------------------------------------------------

lib/Sema/TypeCheckDecl.cpp

@@ -2569,12 +2569,13 @@ InterfaceTypeRequest::evaluate(Evaluator &eval, ValueDecl *D) const {
       ProtocolDecl *errorProto = Context.getErrorDecl();
       if (thrownTy && !thrownTy->hasError() && errorProto) {
         Type thrownTyInContext = AFD->mapTypeIntoContext(thrownTy);
-        if (!checkConformance(thrownTyInContext, errorProto)) {
-          SourceLoc loc;
-          if (auto thrownTypeRepr = AFD->getThrownTypeRepr())
-            loc = thrownTypeRepr->getLoc();
-          else
-            loc = AFD->getLoc();
+        auto thrownTypeRepr = AFD->getThrownTypeRepr();
+        SourceLoc loc =
+            (thrownTypeRepr) ? thrownTypeRepr->getLoc() : AFD->getLoc();
+        if (AFD->getAttrs().hasAttribute<ObjCAttr>()) {
+          Context.Diags.diagnose(loc, diag::typed_thrown_in_objc_forbidden,
+                                 thrownTy);
+        } else if (!checkConformance(thrownTyInContext, errorProto)) {
           Context.Diags.diagnose(loc, diag::thrown_type_not_error, thrownTy);
         }
       }

test/decl/func/typed_throws.swift

@@ -216,3 +216,9 @@ struct NotAnError<T> {}
 
 func badThrowingFunctionType<T>(_: () throws(NotAnError<T>) -> ()) {}
 // expected-error@-1 {{thrown type 'NotAnError<T>' does not conform to the 'Error' protocol}}
+
+enum ObjCError: Int, Error {
+  case Others
+}
+@objc func objcTypedThrow() throws(ObjCError) -> () {}
+// expected-error@-1 {{typed throw can't be applied to @objc functions}}