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

3 files changed, 58 insertions, 0 deletions

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 36232b1e98a..7df189d5f95 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3542,6 +3542,11 @@ def err_member_not_yet_instantiated : Error<
 def note_non_instantiated_member_here : Note<
   "not-yet-instantiated member is declared here">;
 
+def err_enumerator_does_not_exist : Error<
+  "enumerator %0 does not exist in instantiation of %1">;
+def note_enum_specialized_here : Note<
+  "enum %0 was explicitly specialized here">;
+
 def err_member_redeclared : Error<"class member cannot be redeclared">;
 def err_member_name_of_class : Error<"member %0 has the same name as its class">;
 def err_member_def_undefined_record : Error<
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 8729a39f9bc..e767f6a7d9f 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -3289,6 +3289,20 @@ NamedDecl *Sema::FindInstantiatedDecl(SourceLocation Loc, NamedDecl *D,
           << D->getDeclName()
           << Context.getTypeDeclType(cast<CXXRecordDecl>(ParentDC));
         Diag(D->getLocation(), diag::note_non_instantiated_member_here);
+      } else if (EnumConstantDecl *ED = dyn_cast<EnumConstantDecl>(D)) {
+        // This enumeration constant was found when the template was defined,
+        // but can't be found in the instantiation. This can happen if an
+        // unscoped enumeration member is explicitly specialized.
+        EnumDecl *Enum = cast<EnumDecl>(ED->getLexicalDeclContext());
+        EnumDecl *Spec = cast<EnumDecl>(FindInstantiatedDecl(Loc, Enum,
+                                                             TemplateArgs));
+        assert(Spec->getTemplateSpecializationKind() ==
+                 TSK_ExplicitSpecialization);
+        Diag(Loc, diag::err_enumerator_does_not_exist)
+          << D->getDeclName()
+          << Context.getTypeDeclType(cast<TypeDecl>(Spec->getDeclContext()));
+        Diag(Spec->getLocation(), diag::note_enum_specialized_here)
+          << Context.getTypeDeclType(Spec);
       } else {
         // We should have found something, but didn't.
         llvm_unreachable("Unable to find instantiation of declaration!");
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
+}