Address comments

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

Author: DataCorrupted

include/swift/AST/DiagnosticsSema.def

@@ -5461,8 +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,
-      "@objc functions cannot have typed throw", ())
+ERROR(typed_throw_in_objc_forbidden,none,
+      "typed 'throws' %kindonly0 cannot be represented in Objective-C",
+      (const AbstractFunctionDecl *))
 
 //------------------------------------------------------------------------------
 // MARK: Concurrency

lib/Sema/TypeCheckDeclObjC.cpp

@@ -809,26 +809,23 @@ bool swift::isRepresentableInLanguage(
       return false;
     }
   }
-  auto isTypedThrow = [&]() {
-    // With no AST token this should be `throws`
-    if (!AFD->getThrownTypeRepr())
-      return false;
-    // Or it is a `throws(<ErrorType>)`
-    CanType thrownType = AFD->getThrownInterfaceType()->getCanonicalType();
+
+  // Check that @objc functions can't have typed throw.
+  if (AFD->hasThrows()) {
+    Type thrownType = AFD->getThrownInterfaceType();
     // TODO: only `throws(Error)` is allowed.
     // Throwing `any MyError` that confronts `Error` is not implemented yet.
     // Shall we allow `any MyError` in the future, we should check against
-    // `isExistentialType` instead.
-    if (thrownType->isErrorExistentialType())
+    // `isExistentialType` instead, and other type checks will make sure it
+    // confrons to `Error`.
+    if (thrownType && !thrownType->isErrorExistentialType()) {
+      softenIfAccessNote(AFD, Reason.getAttr(),
+                         AFD->diagnose(diag::typed_throw_in_objc_forbidden, AFD)
+                             .limitBehavior(behavior));
+      Reason.describe(AFD);
       return false;
-    softenIfAccessNote(AFD, Reason.getAttr(),
-                       AFD->diagnose(diag::typed_thrown_in_objc_forbidden)
-                           .limitBehavior(behavior));
-    Reason.describe(AFD);
-    return true;
-  };
-  if (AFD->hasThrows() && isTypedThrow()) 
-    return false;
+    }
+  }
 
   if (AFD->hasAsync()) {
     // Asynchronous functions move all of the result value and thrown error

test/attr/attr_objc.swift

@@ -2337,10 +2337,12 @@ class ClassThrows1 {
 
   @objc func throwsError() throws(Error) {}
   @objc func throwsMyError() throws(MyError) {}
-  // expected-error@-1{{@objc functions cannot have typed throw}}
+  // expected-error@-1{{typed 'throws' instance method cannot be represented in Objective-C}}
   // expected-error@-2{{thrown type 'any MyError' does not conform to the 'Error' protocol}}
   @objc func throwsObjCError() throws(ObjCError) {}
-  // expected-error@-1{{@objc functions cannot have typed throw}}
+  // expected-error@-1{{typed 'throws' instance method cannot be represented in Objective-C}}
+  @objc static func throwsObjCErrorClass() throws(ObjCError) {}
+  // expected-error@-1{{typed 'throws' static method cannot be represented in Objective-C}}
 }
 
 

test/attr/attr_objc_async.swift

@@ -56,7 +56,7 @@ actor MyActor {
 
   @objc func objcAsyncThrowsError() async throws(Error) -> Void {}
   @objc func objcAsyncThrowsObjCError() async throws(ObjCError) -> Void {}
-  // expected-error@-1 {{@objc functions cannot have typed throw}}
+  // expected-error@-1 {{typed 'throws' instance method cannot be represented in Objective-C}}
 }
 
 actor class MyActor2 { }