Objective-C++ implicit ivar access uses local `self` shadow rather than method's implicit `self`

[mwyman]

C++ skips the Objective-C name lookup behavior that filters non-implicit-self, and will instead find local variables that shadow self:

__attribute__((objc_root_class))
@interface TestClass
@end

extern TestClass *CreateObject(void) __attribute__((ns_returns_retained));

@implementation TestClass {
  int _value;
}

- (void)foo {
  _value = 0;
  {
    TestClass *self = CreateObject();
    _value = 42;  // In ObjC, this updates the method's self, in ObjC++ it modifies local shadow.
  }
}
@end

When this shadowing occurs in a block, in Objective-C++ the -Wimplicit-retain-self warning is still emitted on bare ivar access but the ivar updates the local ivar on the local self and does not trigger a strong retain of the implicit self from the method.

It appears that Sema::CppLookupName is missing a similar check for non-implicit-self names (e.g. here).

[llvmbot]

@llvm/issue-subscribers-clang-codegen

[mwyman]

Proposed fix at https://reviews.llvm.org/D128556

[llvmbot]

@llvm/issue-subscribers-clang-frontend