CWG2352: Allow qualification conversions during reference binding.

The language wording change forgot to update overload resolution to rank
implicit conversion sequences based on qualification conversions in
reference bindings. The anticipated resolution for that oversight is
implemented here -- we order candidates based on qualification
conversion, not only on top-level cv-qualifiers.

For OpenCL/C++, this allows reference binding between pointers with
differing (nested) address spaces. This makes the behavior of reference
binding consistent with that of implicit pointer conversions, as is the
purpose of this change, but that pre-existing behavior for pointer
conversions is itself probably not correct. In any case, it's now
consistently the same behavior and implemented in only one place.

1 files changed, 7 insertions, 1 deletions

diff --git a/clang/lib/Sema/SemaInit.cpp b/clang/lib/Sema/SemaInit.cpp
index 94d524a63f5..ef4fa827064 100644
--- a/clang/lib/Sema/SemaInit.cpp
+++ b/clang/lib/Sema/SemaInit.cpp
@@ -8919,11 +8919,17 @@ bool InitializationSequence::Diagnose(Sema &S,
       S.Diag(Kind.getLocation(), diag::err_reference_bind_drops_quals)
           << NonRefType << SourceType << 1 /*addr space*/
           << Args[0]->getSourceRange();
-    else
+    else if (DroppedQualifiers.hasQualifiers())
       S.Diag(Kind.getLocation(), diag::err_reference_bind_drops_quals)
           << NonRefType << SourceType << 0 /*cv quals*/
           << Qualifiers::fromCVRMask(DroppedQualifiers.getCVRQualifiers())
           << DroppedQualifiers.getCVRQualifiers() << Args[0]->getSourceRange();
+    else
+      // FIXME: Consider decomposing the type and explaining which qualifiers
+      // were dropped where, or on which level a 'const' is missing, etc.
+      S.Diag(Kind.getLocation(), diag::err_reference_bind_drops_quals)
+          << NonRefType << SourceType << 2 /*incompatible quals*/
+          << Args[0]->getSourceRange();
     break;
   }