[PATCH] Clean up conditionals for declaration of gets().

[Zack Weinberg <zackw at panix dot com>]

gets() has the dubious honor of being the only C89 library feature
that has been completely removed from the current C and C++ standards.
glibc follows suit by not declaring it in _GNU_SOURCE mode either, but
it remains present in older compatibility modes.  Internally, two test
cases need to see stdio.h make the declaration, but all our internal
code is of course compiled under _GNU_SOURCE.  This is currently
kludged by duplicating the gets declaration, fortify wrapper and all,
in include/stdio.h.  Also, the conditional in the public headers for
deciding when to declare gets is complicated and repeated in two places.

This patch adds a new macro to features.h that encapsulates the
complicated rule for when to declare gets.  stdio.h and bits/stdio2.h
can simply test __GLIBC_USE (DEPRECATED_GETS).  Then, instead of
having a duplicate gets declaration in include/stdio.h,
debug/tst-chk1.c and stdio-common/tst-gets.c force that flag on.

Tested on x86_64-linux-gnu, OK?

(If you're wondering why this patch doesn't touch libio/iogets.c, it is
because that file defines _IO_gets, not gets.  Yes, this raises
troubling questions about inconsistencies between the internal
declarations in libioP.h and the public ones in stdio.h.)

zw

        * include/features.h (__GLIBC_USE_DEPRECATED_GETS): New macro.
        * libio/stdio.h, libio/bits/stdio2.h: Condition gets on
        __GLIBC_USE (DEPRECATED_GETS).  Update comments to indicate
        gets was removed from C++ in C++14.
        * include/stdio.h [!_ISOMAC]: Force gets to be declared by
        libio/stdio.h, instead of repeating its declaration.
        * debug/tst-chk1.c, stdio-common/tst-gets.c: Force gets to
        be declared, since we are testing it.
        * stdio-common/Makefile (tst-gets.c): Compile with
        -Wno-deprecated-declarations.
---
 debug/tst-chk1.c        |  5 +++++
 include/features.h      |  9 +++++++++
 include/stdio.h         | 18 ------------------
 libio/bits/stdio2.h     |  3 +--
 libio/stdio.h           | 13 +++++--------
 stdio-common/Makefile   |  3 +++
 stdio-common/tst-gets.c |  6 +++++-
 7 files changed, 28 insertions(+), 29 deletions(-)

diff --git a/debug/tst-chk1.c b/debug/tst-chk1.c
index 478c2fb..3e9d3a5 100644
--- a/debug/tst-chk1.c
+++ b/debug/tst-chk1.c
@@ -16,6 +16,11 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 +/* This file tests gets().  Force it to be declared.  */
+#include <features.h>
+#undef __GLIBC_USE_DEPRECATED_GETS
+#define __GLIBC_USE_DEPRECATED_GETS 1
+
 #include <assert.h>
 #include <fcntl.h>
 #include <locale.h>
diff --git a/include/features.h b/include/features.h
index 650d4c5..94feb1d 100644
--- a/include/features.h
+++ b/include/features.h
@@ -370,6 +370,15 @@
 # define __USE_FORTIFY_LEVEL 0
 #endif
 +/* The function 'gets' existed in C89, but is impossible to use safely.
+   It has been removed from ISO C11, ISO C++14, and _GNU_SOURCE.  */
+#if !defined __USE_ISOC11 \
+    || (defined __cplusplus && __cplusplus <= 201103L)
+# define __GLIBC_USE_DEPRECATED_GETS 1
+#else
+# define __GLIBC_USE_DEPRECATED_GETS 0
+#endif
+
 /* Get definitions of __STDC_* predefined macros, if the compiler has
    not preincluded this header automatically.  */
 #include <stdc-predef.h>
diff --git a/include/stdio.h b/include/stdio.h
index 266c3bb..5965439 100644
--- a/include/stdio.h
+++ b/include/stdio.h
@@ -178,24 +178,6 @@ libc_hidden_proto (__vasprintf_chk)
 libc_hidden_proto (__vdprintf_chk)
 libc_hidden_proto (__obstack_vprintf_chk)
 -/* The <stdio.h> header does not include the declaration for gets
-   anymore when compiling with _GNU_SOURCE.  Provide a copy here.  */
-extern char *gets (char *__s);
-#  if __USE_FORTIFY_LEVEL > 0
-extern char *__gets_chk (char *__str, size_t) __wur;
-extern char *__REDIRECT (__gets_warn, (char *__str), gets)
-     __wur __warnattr ("please use fgets or getline instead, gets can't "
-		       "specify buffer size");
-
-__fortify_function __wur char *
-gets (char *__str)
-{
-  if (__bos (__str) != (size_t) -1)
-    return __gets_chk (__str, __bos (__str));
-  return __gets_warn (__str);
-}
-#  endif
-
 extern FILE * __fmemopen (void *buf, size_t len, const char *mode);
 libc_hidden_proto (__fmemopen)
 diff --git a/libio/bits/stdio2.h b/libio/bits/stdio2.h
index fa3be79..df9662c 100644
--- a/libio/bits/stdio2.h
+++ b/libio/bits/stdio2.h
@@ -222,8 +222,7 @@ __NTH (obstack_vprintf (struct obstack *__restrict
__obstack,
  #endif
 -#if !defined __USE_ISOC11 \
-    || (defined __cplusplus && __cplusplus <= 201103L && !defined
__USE_GNU)
+#if __GLIBC_USE (DEPRECATED_GETS)
 extern char *__gets_chk (char *__str, size_t) __wur;
 extern char *__REDIRECT (__gets_warn, (char *__str), gets)
      __wur __warnattr ("please use fgets or getline instead, gets can't "
diff --git a/libio/stdio.h b/libio/stdio.h
index e37f901..792604f 100644
--- a/libio/stdio.h
+++ b/libio/stdio.h
@@ -625,16 +625,13 @@ __BEGIN_NAMESPACE_STD
 extern char *fgets (char *__restrict __s, int __n, FILE *__restrict
__stream)
      __wur;
 -#if !defined __USE_ISOC11 \
-    || (defined __cplusplus && __cplusplus <= 201103L)
+#if __GLIBC_USE (DEPRECATED_GETS)
 /* Get a newline-terminated string from stdin, removing the newline.
-   DO NOT USE THIS FUNCTION!!  There is no limit on how much it will read.
 -   The function has been officially removed in ISO C11.  This opportunity
-   is used to also remove it from the GNU feature list.  It is now only
-   available when explicitly using an old ISO C, Unix, or POSIX standard.
-   GCC defines _GNU_SOURCE when building C++ code and the function is still
-   in C++11, so it is also available for C++.
+   This function is impossible to use safely.  It has been officially
+   removed from ISO C11 and ISO C++14, and we have also removed it
+   from the _GNU_SOURCE feature list.  It remains available when
+   explicitly using an old ISO C, Unix, or POSIX standard.
     This function is a possible cancellation point and therefore not
    marked with __THROW.  */
diff --git a/stdio-common/Makefile b/stdio-common/Makefile
index 4c4834b..dcbf103 100644
--- a/stdio-common/Makefile
+++ b/stdio-common/Makefile
@@ -141,6 +141,9 @@ CFLAGS-scanf15.c = -I../libio -I../stdlib
-I../wcsmbs -I../time -I../string \
 CFLAGS-scanf17.c = -I../libio -I../stdlib -I../wcsmbs -I../time
-I../string \
 		   -I../wctype
 +# tst-gets.c tests a deprecated function.
+CFLAGS-tst-gets.c += -Wno-deprecated-declarations
+
 CPPFLAGS += $(libio-mtsafe)
  $(objpfx)tst-setvbuf1.out: /dev/null $(objpfx)tst-setvbuf1
diff --git a/stdio-common/tst-gets.c b/stdio-common/tst-gets.c
index 073bc54..b12a7ed 100644
--- a/stdio-common/tst-gets.c
+++ b/stdio-common/tst-gets.c
@@ -17,10 +17,14 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 +/* This file tests gets().  Force it to be declared.  */
+#include <features.h>
+#undef __GLIBC_USE_DEPRECATED_GETS
+#define __GLIBC_USE_DEPRECATED_GETS 1
+
 #include <stdio.h>
 #include <string.h>
 -
 static int
 do_test (void)
 {
-- 
2.10.2