libstdc++/77795 Only declare ::gets for C++98 and C++11

	PR libstdc++/77795
	* acinclude.m4 (GLIBCXX_CHECK_STDIO_PROTO): Use -std=gnu++11 to check
	for gets.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* include/c_global/cstdio [!_GLIBCXX_HAVE_GETS] (gets): Only declare
	for C++98 and C++11.
	* include/c_std/cstdio [!_GLIBCXX_HAVE_GETS] (gets): Likewise.
	* testsuite/27_io/headers/cstdio/functions_neg.cc: New test.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-6-branch@240674 138bc75d-0d04-0410-961f-82ee72b054a4

7 files changed, 49 insertions, 4 deletions

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index d3f3fcd5269..d02668823bb 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,15 @@
 2016-09-30  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/77795
+	* acinclude.m4 (GLIBCXX_CHECK_STDIO_PROTO): Use -std=gnu++11 to check
+	for gets.
+	* config.h.in: Regenerate.
+	* configure: Regenerate.
+	* include/c_global/cstdio [!_GLIBCXX_HAVE_GETS] (gets): Only declare
+	for C++98 and C++11.
+	* include/c_std/cstdio [!_GLIBCXX_HAVE_GETS] (gets): Likewise.
+	* testsuite/27_io/headers/cstdio/functions_neg.cc: New test.
+
 	PR libstdc++/77801
 	* include/experimental/numeric: Include <numeric>.
 	(__abs): Define.
diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index 4769f14d12f..43bece13686 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -2153,6 +2153,10 @@ AC_DEFUN([GLIBCXX_CHECK_STDIO_PROTO], [
 
   AC_LANG_SAVE
   AC_LANG_CPLUSPLUS
+  # Use C++11 because a conforming <stdio.h> won't define gets for C++14,
+  # and we don't need a declaration for C++14 anyway.
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -std=gnu++11"
 
   AC_MSG_CHECKING([for gets declaration])
   AC_CACHE_VAL(glibcxx_cv_gets, [
@@ -2168,10 +2172,11 @@ AC_DEFUN([GLIBCXX_CHECK_STDIO_PROTO], [
       )])
 
   if test $glibcxx_cv_gets = yes; then
-    AC_DEFINE(HAVE_GETS, 1, [Define if gets is available in <stdio.h>.])
+    AC_DEFINE(HAVE_GETS, 1, [Define if gets is available in <stdio.h> before C++14.])
   fi
   AC_MSG_RESULT($glibcxx_cv_gets)
 
+  CXXFLAGS="$ac_save_CXXFLAGS"
   AC_LANG_RESTORE
 ])
 
diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
index 701d4796d38..0a84fba7322 100644
--- a/libstdc++-v3/config.h.in
+++ b/libstdc++-v3/config.h.in
@@ -180,7 +180,7 @@
 /* Define if _Unwind_GetIPInfo is available. */
 #undef HAVE_GETIPINFO
 
-/* Define if gets is available in <stdio.h>. */
+/* Define if gets is available in <stdio.h> before C++14. */
 #undef HAVE_GETS
 
 /* Define to 1 if you have the `hypot' function. */
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index efb382c7edf..bbbcd5d7ce0 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -18175,6 +18175,10 @@ ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
 ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
 ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
 
+  # Use C++11 because a conforming <stdio.h> won't define gets for C++14,
+  # and we don't need a declaration for C++14 anyway.
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -std=gnu++11"
 
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for gets declaration" >&5
 $as_echo_n "checking for gets declaration... " >&6; }
@@ -18209,6 +18213,7 @@ $as_echo "#define HAVE_GETS 1" >>confdefs.h
   { $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_gets" >&5
 $as_echo "$glibcxx_cv_gets" >&6; }
 
+  CXXFLAGS="$ac_save_CXXFLAGS"
   ac_ext=c
 ac_cpp='$CPP $CPPFLAGS'
 ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
diff --git a/libstdc++-v3/include/c_global/cstdio b/libstdc++-v3/include/c_global/cstdio
index 920d109bcb8..86d524f96a6 100644
--- a/libstdc++-v3/include/c_global/cstdio
+++ b/libstdc++-v3/include/c_global/cstdio
@@ -44,7 +44,7 @@
 #ifndef _GLIBCXX_CSTDIO
 #define _GLIBCXX_CSTDIO 1
 
-#ifndef _GLIBCXX_HAVE_GETS
+#if __cplusplus <= 201103L && !defined(_GLIBCXX_HAVE_GETS)
 extern "C" char* gets (char* __s) __attribute__((__deprecated__));
 #endif
 
diff --git a/libstdc++-v3/include/c_std/cstdio b/libstdc++-v3/include/c_std/cstdio
index a4119ba6c64..549004c0a16 100644
--- a/libstdc++-v3/include/c_std/cstdio
+++ b/libstdc++-v3/include/c_std/cstdio
@@ -44,7 +44,7 @@
 #include <bits/c++config.h>
 #include <stdio.h>
 
-#ifndef _GLIBCXX_HAVE_GETS
+#if __cplusplus <= 201103L && !defined(_GLIBCXX_HAVE_GETS)
 extern "C" char* gets (char* __s) __attribute__((__deprecated__));
 #endif
 
diff --git a/libstdc++-v3/testsuite/27_io/headers/cstdio/functions_neg.cc b/libstdc++-v3/testsuite/27_io/headers/cstdio/functions_neg.cc
new file mode 100644
index 00000000000..f9e5f86ed37
--- /dev/null
+++ b/libstdc++-v3/testsuite/27_io/headers/cstdio/functions_neg.cc
@@ -0,0 +1,25 @@
+// { dg-do compile  { target c++14 } }
+
+// Copyright (C) 2007-2016 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library 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.
+
+// This library 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 this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <cstdio>
+
+namespace gnu
+{
+  using std::gets; // { dg-error "has not been declared" }
+}