re PR c++/92973 (Silently accepting defaulted comparison operators in C++11 .. 17)

	PR c++/92973
	* method.c (early_check_defaulted_comparison): For C++17 and earlier
	diagnose defaulted comparison operators.

	* g++.dg/cpp0x/spaceship-eq1.C: New test.

From-SVN: r279682

gcc/cp/ChangeLog

 2019-12-20  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/92973
+	* method.c (early_check_defaulted_comparison): For C++17 and earlier
+	diagnose defaulted comparison operators.
+
 	PR c++/92666
 	* call.c (convert_arg_to_ellipsis): For floating point or
 	decltype(nullptr) arguments call mark_rvalue_use.

gcc/cp/method.c

@@ -1092,6 +1092,13 @@ early_check_defaulted_comparison (tree fn)
     ctx = DECL_FRIEND_CONTEXT (fn);
   bool ok = true;
 
+  if (cxx_dialect < cxx2a)
+    {
+      error_at (loc, "defaulted %qD only available with %<-std=c++2a%> or "
+		     "%<-std=gnu++2a%>", fn);
+      return false;
+    }
+
   if (!DECL_OVERLOADED_OPERATOR_IS (fn, SPACESHIP_EXPR)
       && !same_type_p (TREE_TYPE (TREE_TYPE (fn)), boolean_type_node))
     {

gcc/testsuite/ChangeLog

 2019-12-20  Jakub Jelinek  <jakub@redhat.com>
 
+	PR c++/92973
+	* g++.dg/cpp0x/spaceship-eq1.C: New test.
+
 	PR c++/92666
 	* g++.dg/warn/Wunused-var-36.C: New test.
 

gcc/testsuite/g++.dg/cpp0x/spaceship-eq1.C

+// PR c++/92973
+// { dg-do compile { target c++11 } }
+
+struct S { bool operator==(const S&) const = default; int s; };	// { dg-error "only available with" "" { target c++17_down } }
+struct T { bool operator!=(const T&) const = default; int t; };	// { dg-error "only available with" "" { target c++17_down } }