[clang] [Clang] Fix Microsoft ABI inheritance model when member pointer is used in a base specifier (PR #91990)

[Reid Kleckner via cfe-commits]

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@@ -9015,11 +9015,20 @@ bool Sema::RequireCompleteTypeImpl(SourceLocation Loc, QualType T,
 
   if (const MemberPointerType *MPTy = T->getAs<MemberPointerType>()) {
     if (!MPTy->getClass()->isDependentType()) {
-      if (getLangOpts().CompleteMemberPointers &&
-          !MPTy->getClass()->getAsCXXRecordDecl()->isBeingDefined() &&
-          RequireCompleteType(Loc, QualType(MPTy->getClass(), 0), Kind,
-                              diag::err_memptr_incomplete))
-        return true;
+      if (getLangOpts().CompleteMemberPointers) {
+        const CXXRecordDecl *RD = MPTy->getClass()->getAsCXXRecordDecl();
+        if (RD->isBeingDefined()) {
+          if (RD->isParsingBaseSpecifiers()) {
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rnk wrote:

I'm struggling to understand why this error diagnostic doesn't fire in your MS ABI test case example that forms a member pointer type in the base specifier list.

https://github.com/llvm/llvm-project/pull/91990