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

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.

clang/lib/AST/ASTContext.cpp

#undef UNEXPECTED_TYPE
   }
   }
   llvm_unreachable("Unhandled Type Class");
 }
 
 static auto unwrapSugar(SplitQualType &T, Qualifiers &QTotal) {
   SmallVector<SplitQualType, 8> R;
   while (true) {
-    QTotal += T.Quals;
+    QTotal.addConsistentQualifiers(T.Quals);
     QualType NT = T.Ty->getLocallyUnqualifiedSingleStepDesugaredType();
     if (NT == QualType(T.Ty, 0))
       break;
     R.push_back(T);
     T = NT.split();
   }
   return R;
 }

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

 @interface Radar12280826
 - (void)createInferiorTransportAndSetEnvironment:(NSMutableDictionary*)environment error:(__autoreleasing NSError*&)error;
 @end
 
 @implementation Radar12280826
 - (void)createInferiorTransportAndSetEnvironment:(NSMutableDictionary*)environment error:(__autoreleasing NSError*&)error {}
 @end
 
+// See https://github.com/llvm/llvm-project/issues/61419
+
+template <class T0, class T1> struct pair {
+  T0 first;
+  T1 second;
+};
+
+NSString *p0, *p1;
+const pair<NSString *, NSString *> p = {p0, p1};
+bool b;
+NSString *t = b ? p.first : p.second;