[PATCH] D47503: Sema: Add a warning for member pointers with incomplete base types.

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added inline comments.


================
Comment at: clang/lib/Sema/SemaType.cpp:7599-7604
+      if (!Context.getDiagnostics().isIgnored(diag::warn_memptr_incomplete,
+                                              Loc) &&
+          !MPTy->getClass()->getAsCXXRecordDecl()->isBeingDefined() &&
+          !isCompleteType(Loc, QualType(MPTy->getClass(), 0)))
+        Diag(Loc, diag::warn_memptr_incomplete)
+            << QualType(MPTy->getClass(), 0);
----------------
It's not reasonable to call `isCompleteType` here; this is non-conforming behavior, and it's not reasonable for a warning flag to change the semantics or interpretation of the program. (We actually rely on this in several ways -- `-Weverything` is not supposed to change the validity of programs, and reuse of implicit modules with different warning flags relies on the property that the compiler behavior is as if we compile with `-Weverything` and then filter the warnings after the fact.)

It seems fine to do this in the MS ABI case, since we will attempt to complete the type anyway in that mode. If you want to apply this more generally, I think there are two options: either add a `-f` flag to carry this semantic change, or figure out whether the type is completable without actually completing it (for example, check whether it's a templated class whose pattern is a definition).


https://reviews.llvm.org/D47503