re PR c++/67240 ([concepts] Implicit conversion constraints are not respected)

	PR c++/67240
	* constraint.cc (satisfy_implicit_conversion_constraint): Also
	check for NULL_TREE.

From-SVN: r227081

gcc/cp/ChangeLog

+2015-08-21  Jason Merrill  <jason@redhat.com>
+
+	PR c++/67240
+	* constraint.cc (satisfy_implicit_conversion_constraint): Also
+	check for NULL_TREE.
+
 2015-08-21  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	* decl.c (grokvardecl): Simplify the latter.

gcc/cp/constraint.cc

@@ -1775,7 +1775,7 @@ satisfy_implicit_conversion_constraint (tree t, tree args,
      of the form TYPE <unspecified> = EXPR.  */
   tree conv =
     perform_direct_initialization_if_possible (type, expr, false, complain);
-  if (conv == error_mark_node)
+  if (conv == NULL_TREE || conv == error_mark_node)
     return boolean_false_node;
   else
     return boolean_true_node;

gcc/testsuite/g++.dg/concepts/iconv1.C

+// PR c++/67240
+// { dg-options -std=c++1z }
+
+int foo(int x)
+{
+    return x;
+}
+ 
+template <typename T>
+concept bool C1 = requires (T x) {
+    {foo(x)} -> int&;
+};
+
+template <typename T>
+concept bool C2 = requires (T x) {
+    {foo(x)} -> void;
+};
+ 
+static_assert( C1<int> );	// { dg-error "assert" }
+static_assert( C2<int> );	// { dg-error "assert" }