[PATCH] Fix PR19169:Crash on invalid attempting to specialize a template method as a template variable

[Karthik Bhat]

Thanks Richard for the review. Updating the patch as per review comments.

http://reviews.llvm.org/D3198

Files:
  include/clang/Basic/DiagnosticSemaKinds.td
  lib/Sema/SemaTemplate.cpp
  test/SemaCXX/cxx1y-variable-templates_top_level.cpp

Index: test/SemaCXX/cxx1y-variable-templates_top_level.cpp
===================================================================
--- test/SemaCXX/cxx1y-variable-templates_top_level.cpp
+++ test/SemaCXX/cxx1y-variable-templates_top_level.cpp
@@ -448,3 +448,13 @@
   static_assert(x<int> == 1, "");
 #endif
 }
+
+namespace PR19169 {
+  template <typename T> int* f();
+  template <typename T> void f();
+  template<> int f<double>; // expected-error {{no variable template matches specialization; did you mean to use 'f' as function template instead?}}
+  
+  template <typename T> void g();
+  template<> int g<double>; // expected-error {{no variable template matches specialization; did you mean to use 'g' as function template instead?}}
+}
+
Index: lib/Sema/SemaTemplate.cpp
===================================================================
--- lib/Sema/SemaTemplate.cpp
+++ lib/Sema/SemaTemplate.cpp
@@ -2420,10 +2420,19 @@
 
   // The template-id must name a variable template.
   VarTemplateDecl *VarTemplate =
-      dyn_cast<VarTemplateDecl>(Name.getAsTemplateDecl());
-  if (!VarTemplate)
+      dyn_cast_or_null<VarTemplateDecl>(Name.getAsTemplateDecl());
+  if (!VarTemplate) {
+    NamedDecl *FnTemplate;
+    if (auto *OTS = Name.getAsOverloadedTemplate())
+      FnTemplate = *OTS->begin();
+    else
+      FnTemplate = dyn_cast_or_null<FunctionTemplateDecl>(Name.getAsTemplateDecl());
+    if (FnTemplate)
+      return Diag(D.getIdentifierLoc(), diag::err_var_spec_no_template_but_method)
+               << FnTemplate->getDeclName();
     return Diag(D.getIdentifierLoc(), diag::err_var_spec_no_template)
              << IsPartialSpecialization;
+  }
 
   // Check for unexpanded parameter packs in any of the template arguments.
   for (unsigned I = 0, N = TemplateArgs.size(); I != N; ++I)
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -3314,6 +3314,9 @@
   "previous declaration of variable template partial specialization is here">;
 def err_var_spec_no_template : Error<
   "no variable template matches%select{| partial}0 specialization">;
+def err_var_spec_no_template_but_method : Error<
+  "no variable template matches specialization; "
+  "did you mean to use %0 as function template instead?">;
   
 // C++ Function template specializations
 def err_function_template_spec_no_match : Error<
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