Fix an assertion failure in unwrapSugar

[ahatanak]

Summary

An assertion in Qualifiers::addObjCLifetime fails when the ObjC lifetime bits are already set.

Instead of calling operator+=, call addConsistentQualifiers, which allows the lifetime bits to be set again as long the new value doesn't conflict with the old value.

This fixes https://github.com/llvm/llvm-project/issues/61419.

[ahatanak]

ping

[mizvekov]

clang/test/SemaObjCXX/arc-objc-lifetime.mm

69–79 ↗

(On Diff #509793)

I think the fix looks good, although this test may be out of place in this file.

Ideally, if I had thought of this test case, it would have gone into clang/test/SemaCXX/sugared-auto.cpp.

The existing tests there would try to trigger this bug through return type deduction, and not through the ternary operator as in your reduction.

A second good option would be to add it to clang/test/SemaCXX/sugar-common-types.cpp, as that tests ternary operator cases, but you would have to extend the compile flags to accept the ObjC++ stuff.

Also, if you want to add an isolated test for a bug in a file where it otherwise doesn't follow the style of the existing tests, we would isolate it in a namespace named after the PR.

Something like:

namespace PR61419 {
....
} // namespace PR61419

This makes it easier to extend and not accidentally break existing tests.

Also, it looks like this test could be a bit more minimal, as suggested in the edit.

[mizvekov]

LGTM

[ahatanak]

Simplify test case and move it to clang/test/SemaCXX/sugar-common-types.cpp.