[ODRHash] Stop hashing `ObjCMethodDecl::isOverriding` as it doesn't capture inherent method quality.

[vsapsai]

Summary

isOverriding depends on the surrounding code and not on the method
itself. That's why it can be different in different modules. And
mismatches shouldn't be an error.

rdar://109481753

[vsapsai]

Thanks for the review!

clang/lib/AST/ODRDiagsEmitter.cpp

bool ODRDiagsEmitter::diagnoseMismatch(
   }
 
   Diag(FirstDecl->getLocation(),
        diag::err_module_odr_violation_mismatch_decl_unknown)
       << FirstID << FirstModule.empty() << FirstModule << FirstDiffType
       << FirstDecl->getSourceRange();
   Diag(SecondDecl->getLocation(),
        diag::note_module_odr_violation_mismatch_decl_unknown)
-      << SecondModule << FirstDiffType << SecondDecl->getSourceRange();
+      << SecondModule.empty() << SecondModule << FirstDiffType
+      << SecondDecl->getSourceRange();
   return true;
 }
 
 bool ODRDiagsEmitter::diagnoseMismatch(
     const ObjCProtocolDecl *FirstProtocol,
     const ObjCProtocolDecl *SecondProtocol,
     const struct ObjCProtocolDecl::DefinitionData *SecondDD) const {
   if (FirstProtocol == SecondProtocol)

clang/lib/AST/ODRHash.cpp

public:
 
   void VisitObjCMethodDecl(const ObjCMethodDecl *Method) {
     ID.AddInteger(Method->getDeclKind());
     Hash.AddBoolean(Method->isInstanceMethod()); // false if class method
     Hash.AddBoolean(Method->isPropertyAccessor());
     Hash.AddBoolean(Method->isVariadic());
     Hash.AddBoolean(Method->isSynthesizedAccessorStub());
     Hash.AddBoolean(Method->isDefined());
-    Hash.AddBoolean(Method->isOverriding());
     Hash.AddBoolean(Method->isDirectMethod());
     Hash.AddBoolean(Method->isThisDeclarationADesignatedInitializer());
     Hash.AddBoolean(Method->hasSkippedBody());
 
     ID.AddInteger(Method->getImplementationControl());
     ID.AddInteger(Method->getMethodFamily());
     ImplicitParamDecl *Cmd = Method->getCmdDecl();
     Hash.AddBoolean(Cmd);

clang/test/Modules/compare-objc-nonisolated-methods.m

+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// Test that different values of `ObjCMethodDecl::isOverriding` in different modules
+// is not an error because it depends on the surrounding code and not on the method itself.
+// RUN: %clang_cc1 -fsyntax-only -verify -I%t/include -fmodules -fimplicit-module-maps -fmodules-cache-path=%t/modules.cache -fmodule-name=Override %t/test-overriding.m
+
+//--- include/Common.h
+@interface NSObject
+@end
+
+//--- include/Indirection.h
+#import <Override.h>
+
+//--- include/module.modulemap
+module Common {
+  header "Common.h"
+  export *
+}
+module Indirection {
+  header "Indirection.h"
+  export *
+}
+module Override {
+  header "Override.h"
+  export *
+}
+
+//--- include/Override.h
+#import <Common.h>
+@interface SubClass: NSObject
+- (void)potentialOverride;
+@end
+
+//--- Override_Internal.h
+#import <Common.h>
+@interface NSObject(InternalCategory)
+- (void)potentialOverride;
+@end
+
+//--- test-overriding.m
+//expected-no-diagnostics
+// Get non-modular version of `SubClass`, so that `-[SubClass potentialOverride]`
+// is an override of a method in `InternalCategory`.
+#import "Override_Internal.h"
+#import <Override.h>
+
+// Get modular version of `SubClass` where `-[SubClass potentialOverride]` is
+// not an override because module "Override" doesn't know about Override_Internal.h.
+#import <Indirection.h>
+
+void triggerOverrideCheck(SubClass *sc) {
+  [sc potentialOverride];
+}