Add a special-case diagnostic for one of the more obnoxious special cases of

unscoped enumeration members: an enumerator name which is visible in the
out-of-class definition of a member of a templated class might not actually
exist in the instantiation of that class, if the enumeration is also lexically
defined outside the class definition and is explicitly specialized.

Depending on the result of a CWG discussion, we may have a different resolution
for a class of problems in this area, but this fixes the immediate issue of a
crash-on-invalid / accepts-invalid (depending on +Asserts). Thanks to Johannes
Schaub for digging into the standard wording to find how this case is currently
specified to behave.

llvm-svn: 153461

1 files changed, 39 insertions, 0 deletions

diff --git a/clang/test/SemaCXX/enum-unscoped-nonexistent.cpp b/clang/test/SemaCXX/enum-unscoped-nonexistent.cpp
new file mode 100644
index 00000000000..d49800caa61
--- /dev/null
+++ b/clang/test/SemaCXX/enum-unscoped-nonexistent.cpp
@@ -0,0 +1,39 @@
+// RUN: %clang_cc1 -std=c++11 -verify %s
+
+struct Base {
+  static const int a = 1;
+};
+template<typename T> struct S : Base {
+  enum E : int;
+  constexpr int f();
+  constexpr int g(); // expected-note {{declared here}}
+  void h();
+};
+template<> enum S<char>::E : int {}; // expected-note {{enum 'S<char>::E' was explicitly specialized here}}
+template<> enum S<short>::E : int { b = 2 };
+template<> enum S<int>::E : int { a = 4 };
+template<typename T> enum S<T>::E : int { b = 8 };
+
+// The unqualified-id here names a member of the non-dependent base class Base
+// and not the injected enumerator name 'a' from the specialization.
+template<typename T> constexpr int S<T>::f() { return a; }
+static_assert(S<char>().f() == 1, "");
+static_assert(S<int>().f() == 1, "");
+
+// The unqualified-id here names a member of the current instantiation, which
+// bizarrely might not exist in some instantiations.
+template<typename T> constexpr int S<T>::g() { return b; } // expected-error {{enumerator 'b' does not exist in instantiation of 'S<char>'}}
+static_assert(S<char>().g() == 1, ""); // expected-note {{here}} expected-error {{not an integral constant expression}} expected-note {{undefined}}
+static_assert(S<short>().g() == 2, "");
+static_assert(S<long>().g() == 8, "");
+
+// 'b' is type-dependent, so these assertions should not fire before 'h' is
+// instantiated.
+template<typename T> void S<T>::h() {
+  char c[S<T>::b];
+  static_assert(b != 8, "");
+  static_assert(sizeof(c) != 8, "");
+}
+void f() {
+  S<short>().h(); // ok, b == 2
+}