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

A template declaration of a template name can be null in case we have a dependent name or a set of function templates.
Hence use dyn_cast_or_null instead of dyn_cast. Also improve the diagnostic emitted in this case.

llvm-svn: 208313

3 files changed, 24 insertions, 2 deletions

diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 27ca1c9346c..e33d2c16666 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3314,6 +3314,9 @@ def note_var_prev_partial_spec_here : Note<
   "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<
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index e21d1eef46d..8c0261381c1 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -2420,10 +2420,19 @@ DeclResult Sema::ActOnVarTemplateSpecialization(
 
   // 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)
diff --git a/clang/test/SemaCXX/cxx1y-variable-templates_top_level.cpp b/clang/test/SemaCXX/cxx1y-variable-templates_top_level.cpp
index 37d5bf3a005..1ff64b334ae 100644
--- a/clang/test/SemaCXX/cxx1y-variable-templates_top_level.cpp
+++ b/clang/test/SemaCXX/cxx1y-variable-templates_top_level.cpp
@@ -448,3 +448,13 @@ namespace PR19152 {
   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?}}
+}
+