[clang] [clang] Implement CWG2815 (PR #132778)

[Younan Zhang via cfe-commits]

================
@@ -5242,10 +5255,12 @@ TryReferenceInit(Sema &S, Expr *Init, QualType DeclType,
     // FIXME: As a speculative fix to a defect introduced by CWG2352, we rank
     // a reference binding that performs a non-top-level qualification
     // conversion as a qualification conversion, not as an identity conversion.
-    ICS.Standard.Third = (RefConv &
-                              Sema::ReferenceConversions::NestedQualification)
-                             ? ICK_Qualification
-                             : ICK_Identity;
+    ICS.Standard.Third =
+        (RefConv & Sema::ReferenceConversions::Function)
+            ? ICK_Function_Conversion
+        : (RefConv & Sema::ReferenceConversions::NestedQualification)
+            ? ICK_Qualification
+            : ICK_Identity;
----------------
zyn0217 wrote:

This is getting complicated. How about
```cpp
if (RefConv & Sema::ReferenceConversions::Function)
  ICS.Standard.Third = ICK_Function_Conversion;
else if (RefConv & Sema::ReferenceConversions::NestedQualification)
  ICS.Standard.Third = ICK_Qualification;
else
  ICS.Standard.Third = ICK_Qualification

```

https://github.com/llvm/llvm-project/pull/132778