[Sema] Prevent using member declaration diagnostic if the base class is invalid.

Summary:
Once a base class has been made invalid (by a static_assert for example) all using-member declarations in the derived classes will result in a "not a base class" diagnostic. This diagnostic is very misleading and should not be emitted.

This change is needed to help libc++ produce reasonable diagnostics in `std::optional` and `std::variant`.  

Reviewers: rsmith, majnemer, aaron.ballman

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D25430

llvm-svn: 283755

1 files changed, 9 insertions, 0 deletions

diff --git a/clang/test/SemaCXX/using-decl-templates.cpp b/clang/test/SemaCXX/using-decl-templates.cpp
index d766bb3ac6b..3b2b8e15c83 100644
--- a/clang/test/SemaCXX/using-decl-templates.cpp
+++ b/clang/test/SemaCXX/using-decl-templates.cpp
@@ -92,3 +92,12 @@ namespace aliastemplateinst {
 
   template struct APtr<int>; // expected-error{{elaborated type refers to a type alias template}}
 }
+
+namespace DontDiagnoseInvalidTest {
+template <bool Value> struct Base {
+  static_assert(Value, ""); // expected-error {{static_assert failed}}
+};
+struct Derived : Base<false> { // expected-note {{requested here}}
+  using Base<false>::Base; // OK. Don't diagnose that 'Base' isn't a base class of Derived.
+};
+} // namespace DontDiagnoseInvalidTest