c++: xobj fn call without obj [PR115783]

The code path for rejecting an object-less call to a non-static member
function should also consider xobj member functions (so that we correctly
reject the below calls with a "cannot call member function without object"
diagnostic).

	PR c++/115783

gcc/cp/ChangeLog:

	* call.cc (build_new_method_call): Generalize METHOD_TYPE
	check to DECL_OBJECT_MEMBER_FUNCTION_P.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp23/explicit-obj-diagnostics11.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit 2ee70c9f83a1033f2897a35bff9e9ffdd03cc651)

gcc/cp/call.cc

@@ -11820,7 +11820,7 @@ build_new_method_call (tree instance, tree fns, vec<tree, va_gc> **args,
 			 fn);
 	    }
 
-	  if (TREE_CODE (TREE_TYPE (fn)) == METHOD_TYPE
+	  if (DECL_OBJECT_MEMBER_FUNCTION_P (fn)
 	      && !DECL_CONSTRUCTOR_P (fn)
 	      && is_dummy_object (instance))
 	    {

gcc/testsuite/g++.dg/cpp23/explicit-obj-diagnostics11.C

@@ -0,0 +1,48 @@
+// PR c++/115783
+// { dg-do compile { target c++23 } }
+
+struct A {
+  int f(this auto);
+
+  static void s() {
+    f(); // { dg-error "without object" }
+  }
+};
+
+int n = A::f(); // { dg-error "without object" }
+
+struct B {
+  void ns() {
+    A::f(); // { dg-error "without object" }
+  }
+
+  static void s() {
+    A::f(); // { dg-error "without object" }
+  }
+};
+
+template<class T>
+struct C {
+  void ns() {
+    A::f(); // { dg-error "without object" }
+    T::f(); // { dg-error "without object" }
+  }
+
+  static void s() {
+    A::f(); // { dg-error "without object" }
+    T::f(); // { dg-error "without object" }
+  };
+};
+
+template struct C<A>;
+
+template<class T>
+struct D : T {
+  void ns() {
+    A::f(); // { dg-error "without object" }
+    T::f(); // { dg-error "not a member of 'B'" }
+  }
+};
+
+template struct D<B>; // { dg-message "required from here" }
+template struct D<A>; // { dg-bogus "required from here" }