P0704R1 - fixing const-qualified pointers to members

	* typeck2.c (build_m_component_ref): Also accept in lower stds with
	a pedwarn.

From-SVN: r254487

gcc/cp/ChangeLog

+2017-11-06  Jason Merrill  <jason@redhat.com>
+
+	P0704R1 - fixing const-qualified pointers to members
+	* typeck2.c (build_m_component_ref): Also accept in lower stds with
+	a pedwarn.
+
 2017-11-06  Paolo Carlini  <paolo.carlini@oracle.com>
 
 	PR c++/65579

gcc/cp/typeck2.c

@@ -1922,17 +1922,26 @@ build_m_component_ref (tree datum, tree component, tsubst_flags_t complain)
 		       ptrmem_type);
 	      return error_mark_node;
 	    }
-	  else if (!lval
-		   && !FUNCTION_RVALUE_QUALIFIED (type)
-		   && (cxx_dialect < cxx2a
-		       || ((type_memfn_quals (type)
-			    & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE))
-			   != TYPE_QUAL_CONST)))
+	  else if (!lval && !FUNCTION_RVALUE_QUALIFIED (type))
 	    {
-	      if (complain & tf_error)
-		error ("pointer-to-member-function type %qT requires an lvalue",
-		       ptrmem_type);
-	      return error_mark_node;
+	      if ((type_memfn_quals (type)
+		   & (TYPE_QUAL_CONST | TYPE_QUAL_VOLATILE))
+		  != TYPE_QUAL_CONST)
+		{
+		  if (complain & tf_error)
+		    error ("pointer-to-member-function type %qT requires "
+			   "an lvalue", ptrmem_type);
+		  return error_mark_node;
+		}
+	      else if (cxx_dialect < cxx2a)
+		{
+		  if (complain & tf_warning_or_error)
+		    pedwarn (input_location, OPT_Wpedantic,
+			     "pointer-to-member-function type %qT requires "
+			     "an lvalue before C++2a", ptrmem_type);
+		  else
+		    return error_mark_node;
+		}
 	    }
 	}
       return build2 (OFFSET_REF, type, datum, component);

gcc/testsuite/g++.dg/cpp2a/ptrmem1a.C

+// P0704R1
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+struct S {
+  void ref() & {}
+  void cref() const& {}
+  void vref() volatile & {}
+  void cvref() const volatile & {}
+};
+
+void
+foo ()
+{
+  S{}.ref();		// { dg-error "argument discards qualifiers" }
+  S{}.cref();
+  S{}.vref();		// { dg-error "argument discards qualifiers" }
+  S{}.cvref();		// { dg-error "argument discards qualifiers" }
+
+  (S{}.*&S::ref)();	// { dg-error "pointer-to-member-function type 'void \\(S::\\*\\)\\(\\) &' requires an lvalue" }
+  (S{}.*&S::cref)();
+  (S{}.*&S::vref)();	// { dg-error "pointer-to-member-function type 'void \\(S::\\*\\)\\(\\) volatile &' requires an lvalue" }
+  (S{}.*&S::cvref)();	// { dg-error "pointer-to-member-function type 'void \\(S::\\*\\)\\(\\) const volatile &' requires an lvalue" }
+}