From 4f9c5f006892b9c118de2407ead4a4337c4c6830 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Fri, 11 Dec 2015 22:39:52 +0000
Subject: [PATCH] Allow non-defining declarations of class template partial
 specializations to have a nested name specifier. Strictly speaking, forward
 declarations of class template partial specializations are not permitted at
 all, but that seems like an obvious wording defect, and if we allow them
 without a nested name specifier we should also allow them with a nested name
 specifier.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@255383 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp                         |  7 ++++-
 .../dcl.spec/dcl.type/dcl.type.elab/p1.cpp    | 26 +++++++++++++++++++
 .../Inputs/submodules-merge-defs/defs.h       |  7 +++++
 3 files changed, 39 insertions(+), 1 deletion(-)
 create mode 100644 test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.elab/p1.cpp

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index f9c1a01426..203adeab8d 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -3780,10 +3780,15 @@ Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
   bool IsExplicitSpecialization =
     !TemplateParams.empty() && TemplateParams.back()->size() == 0;
   if (Tag && SS.isNotEmpty() && !Tag->isCompleteDefinition() &&
-      !IsExplicitInstantiation && !IsExplicitSpecialization) {
+      !IsExplicitInstantiation && !IsExplicitSpecialization &&
+      !isa<ClassTemplatePartialSpecializationDecl>(Tag)) {
     // Per C++ [dcl.type.elab]p1, a class declaration cannot have a
     // nested-name-specifier unless it is an explicit instantiation
     // or an explicit specialization.
+    //
+    // FIXME: We allow class template partial specializations here too, per the
+    // obvious intent of DR1819.
+    //
     // Per C++ [dcl.enum]p1, an opaque-enum-declaration can't either.
     Diag(SS.getBeginLoc(), diag::err_standalone_class_nested_name_specifier)
         << GetDiagnosticTypeSpecifierID(DS.getTypeSpecType()) << SS.getRange();
diff --git a/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.elab/p1.cpp b/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.elab/p1.cpp
new file mode 100644
index 0000000000..e3982fd6a8
--- /dev/null
+++ b/test/CXX/dcl.dcl/dcl.spec/dcl.type/dcl.type.elab/p1.cpp
@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -verify %s -std=c++11
+
+namespace N {
+  struct A;
+  template<typename T> struct B {};
+}
+template<typename T> struct C {};
+struct D {
+  template<typename T> struct A {};
+};
+struct N::A; // expected-error {{cannot have a nested name specifier}}
+
+template<typename T> struct N::B; // expected-error {{cannot have a nested name specifier}}
+template<typename T> struct N::B<T*>; // FIXME: This is technically ill-formed, but that's not the intent.
+template<> struct N::B<int>;
+template struct N::B<float>;
+
+template<typename T> struct C;
+template<typename T> struct C<T*>; // FIXME: This is technically ill-formed, but that's not the intent.
+template<> struct C<int>;
+template struct C<float>;
+
+template<typename T> struct D::A; // expected-error {{cannot have a nested name specifier}}
+template<typename T> struct D::A<T*>; // FIXME: This is technically ill-formed, but that's not the intent.
+template<> struct D::A<int>;
+template struct D::A<float>;
diff --git a/test/Modules/Inputs/submodules-merge-defs/defs.h b/test/Modules/Inputs/submodules-merge-defs/defs.h
index e9d7284719..f6004f0fc8 100644
--- a/test/Modules/Inputs/submodules-merge-defs/defs.h
+++ b/test/Modules/Inputs/submodules-merge-defs/defs.h
@@ -131,3 +131,10 @@ namespace ClassTemplatePartialSpec {
   };
   template<typename A, int B> template<typename C> F<A[B]>::F() {}
 }
+
+struct MemberClassTemplate {
+  template<typename T> struct A;
+};
+template<typename T> struct MemberClassTemplate::A {};
+template<typename T> struct MemberClassTemplate::A<T*> {};
+template<> struct MemberClassTemplate::A<int> {};
-- 
2.40.0