--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/selftest-diagnostic.h	Thu Oct 25 07:37:49 2018 +0900
@@ -0,0 +1,49 @@
+/* Selftest support for diagnostics.
+   Copyright (C) 2016-2018 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_SELFTEST_DIAGNOSTIC_H
+#define GCC_SELFTEST_DIAGNOSTIC_H
+
+/* The selftest code should entirely disappear in a production
+   configuration, hence we guard all of it with #if CHECKING_P.  */
+
+#if CHECKING_P
+
+namespace selftest {
+
+/* Convenience subclass of diagnostic_context for testing
+   the diagnostic subsystem.  */
+
+class test_diagnostic_context : public diagnostic_context
+{
+ public:
+  test_diagnostic_context ();
+  ~test_diagnostic_context ();
+
+  /* Implementation of diagnostic_start_span_fn, hiding the
+     real filename (to avoid printing the names of tempfiles).  */
+  static void
+  start_span_cb (diagnostic_context *context, expanded_location exploc);
+};
+
+} // namespace selftest
+
+#endif /* #if CHECKING_P */
+
+#endif /* GCC_SELFTEST_DIAGNOSTIC_H */