From de09096a9ee7f670dc74c6a5b7771953ffaf5c62 Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Tue, 9 Feb 2010 00:37:32 +0000
Subject: [PATCH] Implement a specific diagnostic when a class template partial
 specialization does not use any of its template parameters, then recover far
 more gracefully. Fixes PR6181.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@95629 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Basic/DiagnosticSemaKinds.td |  2 ++
 lib/Sema/SemaTemplate.cpp                  | 29 +++++++++++++++-------
 test/SemaTemplate/temp_class_spec.cpp      | 13 ++++++++++
 3 files changed, 35 insertions(+), 9 deletions(-)

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 5849d9b1cc..05dca15cae 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1271,6 +1271,8 @@ def err_partial_spec_redeclared : Error<
   "class template partial specialization %0 cannot be redeclared">;
 def note_prev_partial_spec_here : Note<
   "previous declaration of class template partial specialization %0 is here">;
+def err_partial_spec_fully_specialized : Error<
+  "partial specialization of %0 does not use any of its template parameters">;
   
 // C++ Function template specializations
 def err_function_template_spec_no_match : Error<
diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index b77702ba3f..1779bde666 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -3400,12 +3400,23 @@ Sema::ActOnClassTemplateSpecialization(Scope *S, unsigned TagSpec,
 
     // FIXME: Diagnose friend partial specializations
 
-    // FIXME: Template parameter list matters, too
-    ClassTemplatePartialSpecializationDecl::Profile(ID,
-                                                   Converted.getFlatArguments(),
-                                                   Converted.flatSize(),
-                                                    Context);
-  } else
+    if (!Name.isDependent() && 
+        !TemplateSpecializationType::anyDependentTemplateArguments(
+                                             TemplateArgs.getArgumentArray(), 
+                                                         TemplateArgs.size())) {
+      Diag(TemplateNameLoc, diag::err_partial_spec_fully_specialized)
+        << ClassTemplate->getDeclName();
+      isPartialSpecialization = false;
+    } else {
+      // FIXME: Template parameter list matters, too
+      ClassTemplatePartialSpecializationDecl::Profile(ID,
+                                                  Converted.getFlatArguments(),
+                                                      Converted.flatSize(),
+                                                      Context);
+    }
+  }
+  
+  if (!isPartialSpecialization)
     ClassTemplateSpecializationDecl::Profile(ID,
                                              Converted.getFlatArguments(),
                                              Converted.flatSize(),
@@ -3435,7 +3446,7 @@ Sema::ActOnClassTemplateSpecialization(Scope *S, unsigned TagSpec,
   QualType CanonType;
   if (PrevDecl && 
       (PrevDecl->getSpecializationKind() == TSK_Undeclared ||
-       TUK == TUK_Friend)) {
+               TUK == TUK_Friend)) {
     // Since the only prior class template specialization with these
     // arguments was referenced but not declared, or we're only
     // referencing this specialization as a friend, reuse that
@@ -3448,8 +3459,8 @@ Sema::ActOnClassTemplateSpecialization(Scope *S, unsigned TagSpec,
   } else if (isPartialSpecialization) {
     // Build the canonical type that describes the converted template
     // arguments of the class template partial specialization.
-    CanonType = Context.getTemplateSpecializationType(
-                                                  TemplateName(ClassTemplate),
+    TemplateName CanonTemplate = Context.getCanonicalTemplateName(Name);
+    CanonType = Context.getTemplateSpecializationType(CanonTemplate,
                                                   Converted.getFlatArguments(),
                                                   Converted.flatSize());
 
diff --git a/test/SemaTemplate/temp_class_spec.cpp b/test/SemaTemplate/temp_class_spec.cpp
index e86f07a02f..8a07fd7292 100644
--- a/test/SemaTemplate/temp_class_spec.cpp
+++ b/test/SemaTemplate/temp_class_spec.cpp
@@ -348,3 +348,16 @@ namespace PR6025 {
   {
   };
 }
+
+namespace PR6181 {
+  template <class T>
+  class a;
+  
+  class s;
+  
+  template <class U>
+  class a<s> // expected-error{{partial specialization of 'a' does not use any of its template parameters}}
+  {
+  };
+  
+}
-- 
2.40.0