re PR c++/65719 (Link error with constexpr variable template)

	PR c++/65719
	* pt.c (tsubst_decl) [VAR_DECL]: Mark namespace-scope
	variables as DECL_NOT_REALLY_EXTERN.

From-SVN: r224442

gcc/cp/ChangeLog

+2015-06-12  Jason Merrill  <jason@redhat.com>
+
+	PR c++/65719
+	* pt.c (tsubst_decl) [VAR_DECL]: Mark namespace-scope
+	variables as DECL_NOT_REALLY_EXTERN.
+
 2015-06-11  Jason Merrill  <jason@redhat.com>
 
 	PR c++/66445

gcc/cp/pt.c

@@ -11306,8 +11306,7 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
 	  {
 	    /* T is a static data member or namespace-scope entity.
 	       We have to substitute into namespace-scope variables
-	       (even though such entities are never templates) because
-	       of cases like:
+	       (not just variable templates) because of cases like:
 	       
 	         template <class T> void f() { extern T t; }
 
@@ -11468,6 +11467,8 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
 	       initializer is present.  We mimic the non-template
 	       processing here.  */
 	    DECL_EXTERNAL (r) = 1;
+	    if (DECL_NAMESPACE_SCOPE_P (t))
+	      DECL_NOT_REALLY_EXTERN (r) = 1;
 
 	    DECL_TEMPLATE_INFO (r) = build_template_info (tmpl, argvec);
 	    SET_DECL_IMPLICIT_INSTANTIATION (r);

gcc/testsuite/g++.dg/cpp1y/var-templ29.C

+// PR c++/65719
+// { dg-do link { target c++14 } }
+
+struct FunctionObject {
+    void operator()() const { }
+};
+
+template <typename T>
+constexpr FunctionObject f{};
+
+int main() {
+    f<int>();
+}