c++: merge default targs for function templates [PR65396]

We currently merge default template arguments for class templates, but
not for function templates.  This patch fixes this by factoring out the
argument merging logic in redeclare_class_template into a separate
function and using it in duplicate_decls as well.

	PR c++/65396

gcc/cp/ChangeLog:

	* cp-tree.h (merge_default_template_args): Declare.
	* decl.cc (merge_default_template_args): Define, factored out
	from redeclare_class_template.
	(duplicate_decls): Use it when merging member function template
	and free function declarations.
	* pt.cc (redeclare_class_template): Factor out default argument
	merging logic into merge_default_template_args.  Improve location
	of a note when there's a template parameter kind mismatch.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/vt-34314.C: Adjust expected location of
	"redeclared here" note.
	* g++.dg/template/pr92440.C: Likewise.
	* g++.old-deja/g++.pt/redecl1.C: Adjust expected location of
	"redefinition of default argument" error.
	* g++.dg/template/defarg23.C: New test.
	* g++.dg/template/defarg23a.C: New test.

8 files changed, 121 insertions, 42 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index cf08e16..757711b 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -6787,6 +6787,7 @@ extern void note_iteration_stmt_body_end	(bool);
 extern void determine_local_discriminator	(tree);
 extern int decls_match				(tree, tree, bool = true);
 extern bool maybe_version_functions		(tree, tree, bool);
+extern bool merge_default_template_args		(tree, tree, bool);
 extern tree duplicate_decls			(tree, tree,
 						 bool hiding = false,
 						 bool was_hidden = false);
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index de41b4d..48763c4 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -1470,6 +1470,43 @@ duplicate_function_template_decls (tree newdecl, tree olddecl)
   return false;
 }
 
+/* OLD_PARMS is the innermost set of template parameters for some template
+   declaration, and NEW_PARMS is the corresponding set of template parameters
+   for a redeclaration of that template.  Merge the default arguments within
+   these two sets of parameters.  CLASS_P is true iff the template in
+   question is a class template.  */
+
+bool
+merge_default_template_args (tree new_parms, tree old_parms, bool class_p)
+{
+  gcc_checking_assert (TREE_VEC_LENGTH (new_parms)
+		       == TREE_VEC_LENGTH (old_parms));
+  for (int i = 0; i < TREE_VEC_LENGTH (new_parms); i++)
+    {
+      tree new_parm = TREE_VALUE (TREE_VEC_ELT (new_parms, i));
+      tree old_parm = TREE_VALUE (TREE_VEC_ELT (old_parms, i));
+      tree& new_default = TREE_PURPOSE (TREE_VEC_ELT (new_parms, i));
+      tree& old_default = TREE_PURPOSE (TREE_VEC_ELT (old_parms, i));
+      if (new_default != NULL_TREE && old_default != NULL_TREE)
+	{
+	  auto_diagnostic_group d;
+	  error ("redefinition of default argument for %q+#D", new_parm);
+	  inform (DECL_SOURCE_LOCATION (old_parm),
+		  "original definition appeared here");
+	  return false;
+	}
+      else if (new_default != NULL_TREE)
+	/* Update the previous template parameters (which are the ones
+	   that will really count) with the new default value.  */
+	old_default = new_default;
+      else if (class_p && old_default != NULL_TREE)
+	/* Update the new parameters, too; they'll be used as the
+	   parameters for any members.  */
+	new_default = old_default;
+    }
+  return true;
+}
+
 /* If NEWDECL is a redeclaration of OLDDECL, merge the declarations.
    If the redeclaration is invalid, a diagnostic is issued, and the
    error_mark_node is returned.  Otherwise, OLDDECL is returned.
@@ -1990,7 +2027,21 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
 		     template shall be specified on the initial declaration
 		     of the member function within the class template.  */
 		  || CLASSTYPE_TEMPLATE_INFO (CP_DECL_CONTEXT (olddecl))))
-	    check_redeclaration_no_default_args (newdecl);
+	    {
+	      check_redeclaration_no_default_args (newdecl);
+
+	      if (DECL_TEMPLATE_INFO (olddecl)
+		  && DECL_MEMBER_TEMPLATE_P (DECL_TI_TEMPLATE (olddecl)))
+		{
+		  tree new_parms = DECL_TEMPLATE_INFO (newdecl)
+		    ? DECL_INNERMOST_TEMPLATE_PARMS (DECL_TI_TEMPLATE (newdecl))
+		    : INNERMOST_TEMPLATE_PARMS (current_template_parms);
+		  tree old_parms
+		    = DECL_INNERMOST_TEMPLATE_PARMS (DECL_TI_TEMPLATE (olddecl));
+		  merge_default_template_args (new_parms, old_parms,
+					       /*class_p=*/false);
+		}
+	    }
 	  else
 	    {
 	      tree t1 = FUNCTION_FIRST_USER_PARMTYPE (olddecl);
@@ -2235,6 +2286,11 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
 		 translation unit."  */
 	      check_no_redeclaration_friend_default_args
 		(old_result, new_result);
+
+	      tree new_parms = DECL_INNERMOST_TEMPLATE_PARMS (newdecl);
+	      tree old_parms = DECL_INNERMOST_TEMPLATE_PARMS (olddecl);
+	      merge_default_template_args (new_parms, old_parms,
+					   /*class_p=*/false);
 	    }
 	  if (!DECL_UNIQUE_FRIEND_P (old_result))
 	    DECL_UNIQUE_FRIEND_P (new_result) = false;
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index d47483d..c93676e 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -6274,8 +6274,6 @@ redeclare_class_template (tree type, tree parms, tree cons)
     {
       tree tmpl_parm;
       tree parm;
-      tree tmpl_default;
-      tree parm_default;
 
       if (TREE_VEC_ELT (tmpl_parms, i) == error_mark_node
           || TREE_VEC_ELT (parms, i) == error_mark_node)
@@ -6286,8 +6284,6 @@ redeclare_class_template (tree type, tree parms, tree cons)
 	return false;
 
       parm = TREE_VALUE (TREE_VEC_ELT (parms, i));
-      tmpl_default = TREE_PURPOSE (TREE_VEC_ELT (tmpl_parms, i));
-      parm_default = TREE_PURPOSE (TREE_VEC_ELT (parms, i));
 
       /* TMPL_PARM and PARM can be either TYPE_DECL, PARM_DECL, or
 	 TEMPLATE_DECL.  */
@@ -6303,7 +6299,7 @@ redeclare_class_template (tree type, tree parms, tree cons)
 	{
 	  auto_diagnostic_group d;
 	  error ("template parameter %q+#D", tmpl_parm);
-	  inform (input_location, "redeclared here as %q#D", parm);
+	  inform (DECL_SOURCE_LOCATION (parm), "redeclared here as %q#D", parm);
 	  return false;
 	}
 
@@ -6321,28 +6317,6 @@ redeclare_class_template (tree type, tree parms, tree cons)
 	  return false;
 	}
 
-      if (tmpl_default != NULL_TREE && parm_default != NULL_TREE)
-	{
-	  /* We have in [temp.param]:
-
-	     A template-parameter may not be given default arguments
-	     by two different declarations in the same scope.  */
-	  auto_diagnostic_group d;
-	  error_at (input_location, "redefinition of default argument for %q#D", parm);
-	  inform (DECL_SOURCE_LOCATION (tmpl_parm),
-		  "original definition appeared here");
-	  return false;
-	}
-
-      if (parm_default != NULL_TREE)
-	/* Update the previous template parameters (which are the ones
-	   that will really count) with the new default value.  */
-	TREE_PURPOSE (TREE_VEC_ELT (tmpl_parms, i)) = parm_default;
-      else if (tmpl_default != NULL_TREE)
-	/* Update the new parameters, too; they'll be used as the
-	   parameters for any members.  */
-	TREE_PURPOSE (TREE_VEC_ELT (parms, i)) = tmpl_default;
-
       /* Give each template template parm in this redeclaration a
 	 DECL_CONTEXT of the template for which they are a parameter.  */
       if (TREE_CODE (parm) == TEMPLATE_DECL)
@@ -6352,6 +6326,9 @@ redeclare_class_template (tree type, tree parms, tree cons)
 	}
     }
 
+  if (!merge_default_template_args (parms, tmpl_parms, /*class_p=*/true))
+    return false;
+
   tree ci = get_constraints (tmpl);
   tree req1 = ci ? CI_TEMPLATE_REQS (ci) : NULL_TREE;
   tree req2 = cons ? CI_TEMPLATE_REQS (cons) : NULL_TREE;
diff --git a/gcc/testsuite/g++.dg/cpp0x/vt-34314.C b/gcc/testsuite/g++.dg/cpp0x/vt-34314.C
index b37cac5..704a975 100644
--- a/gcc/testsuite/g++.dg/cpp0x/vt-34314.C
+++ b/gcc/testsuite/g++.dg/cpp0x/vt-34314.C
@@ -3,8 +3,8 @@
 template<typename Fun, typename... Args> // { dg-error "template parameter" }
 struct call;
 
-template<typename Fun, typename Arg0>
-struct call // { dg-message "note: redeclared here" }
+template<typename Fun, typename Arg0> // { dg-message "note: redeclared here" }
+struct call
 {
     template<typename Sig>
     struct result;
@@ -20,8 +20,8 @@ struct call // { dg-message "note: redeclared here" }
 template<typename Fun, int... N> // { dg-error "template parameter" }
 struct call2;
 
-template<typename Fun, int N>
-struct call2 // { dg-message "note: redeclared here" }
+template<typename Fun, int N> // { dg-message "note: redeclared here" }
+struct call2
 {
     template<typename Sig>
     struct result;
@@ -36,8 +36,8 @@ struct call2 // { dg-message "note: redeclared here" }
 template<typename Fun, template<typename> class... TT> // { dg-error "template parameter" }
 struct call3;
 
-template<typename Fun, template<typename> class TT>
-struct call3 // { dg-message "note: redeclared here" }
+template<typename Fun, template<typename> class TT> // { dg-message "note: redeclared here" }
+struct call3
 {
     template<typename Sig>
     struct result;
diff --git a/gcc/testsuite/g++.dg/template/defarg23.C b/gcc/testsuite/g++.dg/template/defarg23.C
new file mode 100644
index 0000000..443d026
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/defarg23.C
@@ -0,0 +1,21 @@
+// PR c++/65396
+// { dg-do compile { target c++11 } }
+
+template<class T>     void f();
+template<class T=int> void f();
+
+template<class T=int> void g(); // { dg-message "original definition" }
+template<class T=int> void g(); // { dg-error "redefinition of default" }
+
+template<class T, class U=bool> void h();
+template<class T=char, class U>
+void h() {
+  static_assert(__is_same(T, char), "");
+  static_assert(__is_same(U, bool), "");
+}
+
+int main() {
+  f();
+  g();
+  h();
+}
diff --git a/gcc/testsuite/g++.dg/template/defarg23a.C b/gcc/testsuite/g++.dg/template/defarg23a.C
new file mode 100644
index 0000000..3de0306
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/defarg23a.C
@@ -0,0 +1,24 @@
+// PR c++/65396
+// { dg-do compile { target c++11 } }
+// Like defarg23.C, but for member functions.
+
+struct A {
+  template<class T> void f();
+  template<class T=int> void g(); // { dg-message "original definition" }
+  template<class T=char, class U> void h();
+};
+
+template<class T=int> void A::f() { }
+template<class T=int> void A::g() { } // { dg-error "redefinition of default" }
+template<class T, class U=bool>
+void A::h() {
+  static_assert(__is_same(T, char), "");
+  static_assert(__is_same(U, bool), "");
+}
+
+int main() {
+  A a;
+  a.f();
+  a.g();
+  a.h();
+}
diff --git a/gcc/testsuite/g++.dg/template/pr92440.C b/gcc/testsuite/g++.dg/template/pr92440.C
index 20db5f1..f1e9281 100644
--- a/gcc/testsuite/g++.dg/template/pr92440.C
+++ b/gcc/testsuite/g++.dg/template/pr92440.C
@@ -3,8 +3,8 @@
 
 template <int T> // { dg-error "template parameter" }
 struct S {
-    template <class U>
-    friend struct S;  // { dg-message "note: redeclared here as" }
+    template <class U> // { dg-message "note: redeclared here as" }
+    friend struct S;
 };
 
 S<0> s;
diff --git a/gcc/testsuite/g++.old-deja/g++.pt/redecl1.C b/gcc/testsuite/g++.old-deja/g++.pt/redecl1.C
index 48517f5d..7596513 100644
--- a/gcc/testsuite/g++.old-deja/g++.pt/redecl1.C
+++ b/gcc/testsuite/g++.old-deja/g++.pt/redecl1.C
@@ -9,14 +9,14 @@ struct S1 {}; // { dg-error "redeclared" } used 1 template parameter
 template <class T = int> // { dg-message "original definition" }
 struct S2; 
 
-template <class T = int>
-struct S2; // { dg-error "redefinition of default" } 
+template <class T = int> // { dg-error "redefinition of default" } 
+struct S2;
 
 template <class T> // { dg-error "template parameter" } 
 struct S3;
 
-template <int I>
-struct S3; // { dg-message "note: redeclared here" } 
+template <int I> // { dg-message "note: redeclared here" } 
+struct S3;
 
-template <template <class T> class C>
-struct S3; // { dg-message "note: redeclared here" } 
+template <template <class T> class C> // { dg-message "note: redeclared here" } 
+struct S3;