Correct handling of pointers into anonymous unions.

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -7061,6 +7061,8 @@ def err_illegal_decl_mempointer_to_reference : Error<
   "'%0' declared as a member pointer to a reference of type %1">;
 def err_illegal_decl_mempointer_to_void : Error<
   "'%0' declared as a member pointer to void">;
+def err_illegal_decl_mempointer_into_anon_union : Error<
+  "'%0' declared as a member pointer into an anonymous union">;
 def err_illegal_decl_mempointer_in_nonclass
     : Error<"%0 does not point into a class">;
 def err_reference_to_void : Error<"cannot form a reference to 'void'">;

clang/lib/AST/ExprConstantMeta.cpp

@@ -3165,9 +3165,23 @@ bool extract(APValue &Result, ASTContext &C, MetaActions &Meta,
         return Diagnoser(Range.getBegin(), diag::metafn_cannot_extract) << 2
             << DescriptionOf(RV) << Range;
 
-      QualType MemPtrTy = C.getMemberPointerType(
-              Decl->getType(), nullptr,
-              cast<CXXRecordDecl>(Decl->getDeclContext()));
+      DeclContext *ObjDC = Decl->getDeclContext();
+      while (ObjDC &&
+             [](DeclContext *DC) {
+               if (auto *RD = dyn_cast<CXXRecordDecl>(DC))
+                 return RD->isAnonymousStructOrUnion();
+               else return DC->isTransparentContext();
+             }(ObjDC))
+      if (isa<TranslationUnitDecl>(ObjDC))
+        // Can happen if Target was a member of a static anonymous union at
+        // namespace scope.
+        return Diagnoser(Range.getBegin(), diag::metafn_cannot_extract) << 2
+            << "a field that is not a member of a class";
+      else
+        ObjDC = ObjDC->getParent();
+
+      QualType MemPtrTy = C.getMemberPointerType(Decl->getType(), nullptr,
+                                                 cast<CXXRecordDecl>(ObjDC));
       if (MemPtrTy.getCanonicalType().getTypePtr() !=
           ResultTy.getCanonicalType().getTypePtr())
         return Diagnoser(Range.getBegin(),

clang/lib/Sema/SemaType.cpp

@@ -2718,6 +2718,15 @@ QualType Sema::BuildMemberPointerType(QualType T, const CXXScopeSpec &SS,
     }
   }
 
+  if (Cls && Cls->isAnonymousStructOrUnion()) {
+    auto D = Diag(Loc, diag::err_illegal_decl_mempointer_into_anon_union);
+    if (const IdentifierInfo *II = Entity.getAsIdentifierInfo())
+      D << II;
+    else
+      D << "member pointer";
+    return QualType();
+  }
+
   // Verify that we're not building a pointer to pointer to function with
   // exception specification.
   if (CheckDistantExceptionSpec(T)) {