c++: Diagnose invalid use of member function in requires

This updates diagnose_valid_expression to mirror the convert_to_void check added
to tsubst_valid_expression_requirement by r10-7554.

gcc/cp/ChangeLog:

	PR c++/67825
	* constraint.cc (diagnose_valid_expression): Check convert_to_void here
	as well as in tsubst_valid_expression_requirement.

gcc/testsuite/ChangeLog:

	PR c++/67825
	* g++.dg/concepts/diagnostic10.C: New test.
	* g++.dg/cpp2a/concepts-pr67178.C: Adjust dg-message.

gcc/cp/ChangeLog

+2020-04-22  Patrick Palka  <ppalka@redhat.com>
+
+	PR c++/67825
+	* constraint.cc (diagnose_valid_expression): Check convert_to_void here
+	as well as in tsubst_valid_expression_requirement.
+
 2020-04-21  Patrick Palka  <ppalka@redhat.com>
 
 	PR c++/94549

gcc/cp/constraint.cc

@@ -3242,7 +3242,8 @@ static tree
 diagnose_valid_expression (tree expr, tree args, tree in_decl)
 {
   tree result = tsubst_expr (expr, args, tf_none, in_decl, false);
-  if (result != error_mark_node)
+  if (result != error_mark_node
+      && convert_to_void (result, ICV_STATEMENT, tf_none) != error_mark_node)
     return result;
 
   location_t loc = cp_expr_loc_or_input_loc (expr);
@@ -3250,7 +3251,10 @@ diagnose_valid_expression (tree expr, tree args, tree in_decl)
     {
       /* Replay the substitution error.  */
       inform (loc, "the required expression %qE is invalid, because", expr);
-      tsubst_expr (expr, args, tf_error, in_decl, false);
+      if (result == error_mark_node)
+	tsubst_expr (expr, args, tf_error, in_decl, false);
+      else
+	convert_to_void (result, ICV_STATEMENT, tf_error);
     }
   else
     inform (loc, "the required expression %qE is invalid", expr);

gcc/testsuite/ChangeLog

+2020-04-22  Patrick Palka  <ppalka@redhat.com>
+
+	PR c++/67825
+	* g++.dg/concepts/diagnostic10.C: New test.
+	* g++.dg/cpp2a/concepts-pr67178.C: Adjust dg-message.
+
 2020-04-21  Patrick Palka  <ppalka@redhat.com>
 
 	PR c++/94549
 	* g++.dg/concepts/inherit-ctor3.C: Adjust expected diagnostics.
-	* g++.dg/cpp2a/concepts-inherit-ctor4.C: New test.
+	* g++.dg/cpp2a/concepts-inherit-ctor4.C: Likewise.
 	* g++.dg/cpp2a/concepts-inherit-ctor8.C: New test.
 
 2020-04-21  Jonathan Wakely  <jwakely@redhat.com>

gcc/testsuite/g++.dg/concepts/diagnostic10.C

+// PR c++/67825
+// { dg-do compile { target concepts } }
+// { dg-additional-options "-fconcepts-diagnostics-depth=2" }
+
+template<typename T>
+  requires requires (T t) { t.f; } // { dg-error "invalid use of non-static member function" }
+void foo() { }
+
+struct S
+{
+  int f();
+};
+
+void
+bar()
+{
+  foo<S>(); // { dg-error "unsatisfied constraints" }
+}

gcc/testsuite/g++.dg/cpp2a/concepts-pr67178.C

@@ -12,7 +12,7 @@ concept C0 = requires (auto x) { // { dg-error "placeholder type" }
 template<typename T>
 concept C1 = requires (C1 auto x) { // { dg-error "not been declared|placeholder|two or more|in requirements" }
   x; // { dg-error "not declared" }
-  { x } -> c; // { dg-message "not declared|does not satisfy" }
+  { x } -> c; // { dg-message "is invalid" }
 };
 
 template<typename T>