Gavin Smith wrote: > AC_PROG_CC_STDC from stdarg.m4 (via gl_PROG_CC_C99 in gnulib-common.m4): > > # gl_PROG_CC_C99 > # Modifies the value of the shell variable CC in an attempt to make $CC > # understand ISO C99 source code. > # This is like AC_PROG_CC_C99, except that > # - AC_PROG_CC_C99 does not mix well with AC_PROG_CC_STDC > # <https://lists.gnu.org/r/bug-gnulib/2011-09/msg00367.html>, > # but many more packages use AC_PROG_CC_STDC than AC_PROG_CC_C99 > # <https://lists.gnu.org/r/bug-gnulib/2011-09/msg00441.html>. > # Remaining problems: > # - When AC_PROG_CC_STDC is invoked twice, it adds the C99 enabling options > # to CC twice > # <https://lists.gnu.org/r/bug-gnulib/2011-09/msg00431.html>. > # - AC_PROG_CC_STDC is likely to change now that C11 is an ISO standard. > AC_DEFUN([gl_PROG_CC_C99], > [ > dnl Change that version number to the minimum Autoconf version that supports > dnl mixing AC_PROG_CC_C99 calls with AC_PROG_CC_STDC calls. > m4_version_prereq([9.0], > [AC_REQUIRE([AC_PROG_CC_C99])], > [AC_REQUIRE([AC_PROG_CC_STDC])]) > ]) > > I'll leave it to someone else to try to fix this.
1) We don't need to care about Autoconf versions any more that didn't have AC_PROG_CC_C99. Gnulib assumes Autoconf >= 2.64. 2) What does it mean that "AC_PROG_CC_C99 does not mix well with AC_PROG_CC_STDC", as stated in <https://lists.gnu.org/r/bug-gnulib/2011-09/msg00367.html>? I did a couple of tests with Autoconf 2.64; the results with 2.69 are the same. A configure script that contains AC_PROG_CC AC_PROG_CC_STDC AC_PROG_CC_C99 produces - with CC="gcc-version 4.2.4": S["CC"]="gcc-version 4.2.4 -std=gnu99 -std=gnu99" - on AIX 7.1 with CC="xlc -qthreaded -qtls": S["CC"]="xlc -qthreaded -qtls" - on Solaris 10 with CC="cc -O": S["CC"]="cc -O -xc99=all -xc99=all" A configure script that contains AC_PROG_CC AC_PROG_CC_C99 AC_PROG_CC_STDC produces - with CC="gcc-version 4.2.4": S["CC"]="gcc-version 4.2.4 -std=gnu99 -std=gnu99" - on AIX 7.1 with CC="xlc -qthreaded -qtls": S["CC"]="xlc -qthreaded -qtls" - on Solaris 10 with CC="cc -O": S["CC"]="cc -O -xc99=all -xc99=all" Typical configure output looks like this: checking whether we are using the GNU C compiler... yes checking whether gcc-version 4.2.4 accepts -g... yes checking for gcc-version 4.2.4 option to accept ISO C89... none needed checking for style of include used by make... GNU checking dependency style of gcc-version 4.2.4... none checking for gcc-version 4.2.4 option to accept ISO C99... -std=gnu99 checking for gcc-version 4.2.4 -std=gnu99 option to accept ISO C99... (cached) -std=gnu99 checking for gcc-version 4.2.4 -std=gnu99 -std=gnu99 option to accept ISO Standard C... (cached) -std=gnu99 So, this works fine. Only a cosmetic problem. The doubling of the option does not occur in GCC versions that support C99 by default, namely in GCC >= 5. So, few people will encounter this cosmetic problem. So, AC_PROG_CC_C99 can be used in place of AC_PROG_CC_STDC always. But with Autoconf 2.69c, this produces a warning: warning: The macro `AC_PROG_CC_C99' is obsolete. I'm therefore committing this fix: 2020-09-27 Bruno Haible <br...@clisp.org> Avoid "warning: The macro `AC_PROG_CC_STDC' is obsolete". Reported by Gavin Smith <gavinsmith0...@gmail.com> in <https://lists.gnu.org/archive/html/bug-gnulib/2020-09/msg00151.html>. * m4/gnulib-common.m4 (gl_PROG_CC_C99): Use AC_PROG_CC_C99 or AC_PROG_CC, depending on the Autoconf version. diff --git a/m4/gnulib-common.m4 b/m4/gnulib-common.m4 index a036454..ddf9e69 100644 --- a/m4/gnulib-common.m4 +++ b/m4/gnulib-common.m4 @@ -1,4 +1,4 @@ -# gnulib-common.m4 serial 61 +# gnulib-common.m4 serial 62 dnl Copyright (C) 2007-2020 Free Software Foundation, Inc. dnl This file is free software; the Free Software Foundation dnl gives unlimited permission to copy and/or distribute it, @@ -483,23 +483,17 @@ AC_DEFUN([gl_FEATURES_H], # gl_PROG_CC_C99 # Modifies the value of the shell variable CC in an attempt to make $CC # understand ISO C99 source code. -# This is like AC_PROG_CC_C99, except that -# - AC_PROG_CC_C99 does not mix well with AC_PROG_CC_STDC -# <https://lists.gnu.org/r/bug-gnulib/2011-09/msg00367.html>, -# but many more packages use AC_PROG_CC_STDC than AC_PROG_CC_C99 -# <https://lists.gnu.org/r/bug-gnulib/2011-09/msg00441.html>. -# Remaining problems: -# - When AC_PROG_CC_STDC is invoked twice, it adds the C99 enabling options -# to CC twice -# <https://lists.gnu.org/r/bug-gnulib/2011-09/msg00431.html>. -# - AC_PROG_CC_STDC is likely to change now that C11 is an ISO standard. AC_DEFUN([gl_PROG_CC_C99], [ - dnl Change that version number to the minimum Autoconf version that supports - dnl mixing AC_PROG_CC_C99 calls with AC_PROG_CC_STDC calls. - m4_version_prereq([9.0], - [AC_REQUIRE([AC_PROG_CC_C99])], - [AC_REQUIRE([AC_PROG_CC_STDC])]) + dnl Just use AC_PROG_CC_C99. + dnl When AC_PROG_CC_C99 and AC_PROG_CC_STDC are used together, the substituted + dnl value of CC will contain the C99 enabling options twice. But this is only + dnl a cosmetic problem. + dnl With Autoconf >= 2.69c, use AC_PROG_CC since it implies AC_PROG_CC_C99; + dnl this avoids a "warning: The macro `AC_PROG_CC_C99' is obsolete." + m4_version_prereq([2.69c], + [AC_REQUIRE([AC_PROG_CC])], + [AC_REQUIRE([AC_PROG_CC_C99])]) ]) # gl_PROG_AR_RANLIB
