C++ PATCH for c++/90884 - stray note with -Wctor-dtor-privacy

[Marek Polacek <polacek@redhat.com>]

This patch fixes a naked inform call, resulting in bogus note in the
following testcase, if not compiled with -Wsystem-headers.

Bootstrap/regtest running on x86_64-linux, ok for trunk?

2019-06-14  Marek Polacek  <polacek@redhat.com>

	PR c++/90884 - stray note with -Wctor-dtor-privacy.
	* class.c (maybe_warn_about_overly_private_class): Guard the call to
	inform.

	* g++.dg/warn/ctor-dtor-privacy-4.C: New.
	* g++.dg/warn/ctor-dtor-privacy-4.h: New.

diff --git gcc/cp/class.c gcc/cp/class.c
index 4fdb0f328cc..de37e43d04c 100644
--- gcc/cp/class.c
+++ gcc/cp/class.c
@@ -2150,10 +2150,10 @@ maybe_warn_about_overly_private_class (tree t)
 
       if (!nonprivate_ctor)
 	{
-	  warning (OPT_Wctor_dtor_privacy,
-		   "%q#T only defines private constructors and has no friends",
-		   t);
-	  if (copy_or_move)
+	  bool w = warning (OPT_Wctor_dtor_privacy,
+			    "%q#T only defines private constructors and has "
+			    "no friends", t);
+	  if (w && copy_or_move)
 	    inform (DECL_SOURCE_LOCATION (copy_or_move),
 		    "%q#D is public, but requires an existing %q#T object",
 		    copy_or_move, t);
diff --git gcc/testsuite/g++.dg/warn/ctor-dtor-privacy-4.C gcc/testsuite/g++.dg/warn/ctor-dtor-privacy-4.C
new file mode 100644
index 00000000000..fcad34e000c
--- /dev/null
+++ gcc/testsuite/g++.dg/warn/ctor-dtor-privacy-4.C
@@ -0,0 +1,5 @@
+// PR c++/90884
+// { dg-options "-Wctor-dtor-privacy" }
+// { dg-prune-output "In file included from" }
+
+#include "ctor-dtor-privacy-4.h"  // { dg-bogus "is public" }
diff --git gcc/testsuite/g++.dg/warn/ctor-dtor-privacy-4.h gcc/testsuite/g++.dg/warn/ctor-dtor-privacy-4.h
new file mode 100644
index 00000000000..d67fd26943e
--- /dev/null
+++ gcc/testsuite/g++.dg/warn/ctor-dtor-privacy-4.h
@@ -0,0 +1,7 @@
+#pragma GCC system_header
+
+namespace std {
+struct __nonesuch {
+  __nonesuch(__nonesuch const &);
+};
+} // namespace std