[Sema] Handle objc_super special lookup when checking builtin compatibility

[tambre]

Summary

objc_super is special and needs LookupPredefedObjCSuperType() called before performing builtin type comparisons.
This fixes an error when compiling macOS headers. A test is added.

[tambre]

I'll go ahead and commit this after the builds pass, as it's affecting an user and the fix is simple and obvious. Hopefully post-commit review is acceptable per my understanding of the rules.

[dmajor]

Thanks, this fixes the specific translation unit I was looking at today. It's going to take some time before I have full build results but I don't expect any problems.

[rjmccall]

clang/lib/Sema/SemaDecl.cpp

9674

Can we avoid doing this except for the small number of builtins that use struct objc_super? We already have the BuiltinID.

[tambre]

clang/lib/Sema/SemaDecl.cpp

9674

LookupPredefedObjCSuperType() already checks if the identifier is "objc_msgSendSuper". But it'd probably be more efficient to check the BuiltinID. I'll follow this up tomorrow.

[rjmccall]

Oh, I didn't notice that this only did work conditionally based on the builtin ID. Yes, please make a function like lookupNecessaryTypesForBuiltin that takes the builtin ID. Maybe we can generalize this to solve the problem with that other builtin, too.

clang/lib/Sema/SemaDecl.cpp

if (IdentifierInfo *II = Previous.getLookupName().getAsIdentifierInfo()) {
         if (NewFD->getLanguageLinkage() == CLanguageLinkage) {
           // Declarations for builtins with custom typechecking by definition
           // don't make sense. Don't attempt typechecking and simply add the
           // attribute.
           if (Context.BuiltinInfo.hasCustomTypechecking(BuiltinID)) {
             NewFD->addAttr(BuiltinAttr::CreateImplicit(Context, BuiltinID));
           } else {
             ASTContext::GetBuiltinTypeError Error;
+            LookupPredefedObjCSuperType(*this, S, NewFD->getIdentifier());
             QualType BuiltinType = Context.GetBuiltinType(BuiltinID, Error);
 
             if (!Error && !BuiltinType.isNull() &&
                 Context.hasSameFunctionTypeIgnoringExceptionSpec(
                     NewFD->getType(), BuiltinType))
               NewFD->addAttr(BuiltinAttr::CreateImplicit(Context, BuiltinID));
           }
         } else if (BuiltinID == Builtin::BI__GetExceptionInfo &&

clang/test/SemaObjCXX/builtin-objcsuper.mm

+// RUN: %clang_cc1 -verify %s
+// expected-no-diagnostics
+
+// objc_super has special lookup rules for compatibility with macOS headers, so
+// the following should compile.
+struct objc_super {};
+extern "C" id objc_msgSendSuper(struct objc_super *super, SEL op, ...);
+extern "C" void objc_msgSendSuper_stret(struct objc_super *super, SEL op, ...);