I asked: > Hi Paul, > > > (I did reproduce the bug). > > Have you reproduced the warning > "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS" > with autoconf 2.63 but not 2.64 ? This is indeed the case. With this simple configure.ac ========================================================== dnl This file is in the public domain. dnl dnl Configuration file - processed by autoconf. AC_INIT([hello-c], [0]) AC_CONFIG_AUX_DIR([build-aux]) AC_CONFIG_SRCDIR([hello.c]) AM_INIT_AUTOMAKE AC_PROG_CC gl_USE_SYSTEM_EXTENSIONS AC_CHECK_HEADERS([unistd.h]) AC_GNU_SOURCE AC_CONFIG_FILES([Makefile]) AC_CONFIG_FILES([m4/Makefile]) AC_OUTPUT ========================================================== and the previous definition of gl_USE_SYSTEM_EXTENSIONS, I observe (with Automake 1.12.6): * with autoconf 2.62 .. 2.63: configure.ac:14: warning: AC_USE_SYSTEM_EXTENSIONS invoked multiple times ../../lib/autoconf/specific.m4:331: AC_GNU_SOURCE is expanded from... configure.ac:14: the top level configure.ac:14: warning: AC_USE_SYSTEM_EXTENSIONS invoked multiple times ../../lib/autoconf/specific.m4:331: AC_GNU_SOURCE is expanded from... configure.ac:14: the top level * with autoconf 2.64 .. 2.69b: no warnings * with autoconf 2.69c: configure.ac:11: warning: The macro `AC_GNU_SOURCE' is obsolete. configure.ac:11: You should run autoupdate. ./lib/autoconf/specific.m4:312: AC_GNU_SOURCE is expanded from... m4/extensions.m4:178: gl_USE_SYSTEM_EXTENSIONS is expanded from... configure.ac:11: the top level configure.ac:14: warning: The macro `AC_GNU_SOURCE' is obsolete. configure.ac:14: You should run autoupdate. ./lib/autoconf/specific.m4:312: AC_GNU_SOURCE is expanded from... configure.ac:14: the top level configure.ac:11: warning: The macro `AC_GNU_SOURCE' is obsolete. configure.ac:11: You should run autoupdate. ./lib/autoconf/specific.m4:312: AC_GNU_SOURCE is expanded from... m4/extensions.m4:178: gl_USE_SYSTEM_EXTENSIONS is expanded from... configure.ac:11: the top level configure.ac:14: warning: The macro `AC_GNU_SOURCE' is obsolete. configure.ac:14: You should run autoupdate. ./lib/autoconf/specific.m4:312: AC_GNU_SOURCE is expanded from... configure.ac:14: the top level Since in Gnulib we assume autoconf >= 2.64 (see NEWS entry from 2020-08-16) we can remove this workaround. 2020-09-27 Bruno Haible <bruno@xxxxxxxxx> extensions: Simplify last commit. * m4/extensions.m4 (gl_USE_SYSTEM_EXTENSIONS): Don't require AC_GNU_SOURCE ever. diff --git a/m4/extensions.m4 b/m4/extensions.m4 index 22fdb03..3179080 100644 --- a/m4/extensions.m4 +++ b/m4/extensions.m4 @@ -1,4 +1,4 @@ -# serial 19 -*- Autoconf -*- +# serial 20 -*- Autoconf -*- # Enable extensions on systems that normally disable them. # Copyright (C) 2003, 2006-2020 Free Software Foundation, Inc. @@ -177,13 +177,5 @@ dnl configure.ac when using autoheader 2.62. # typically due to standards-conformance issues. AC_DEFUN_ONCE([gl_USE_SYSTEM_EXTENSIONS], [ - dnl Require this macro before AC_USE_SYSTEM_EXTENSIONS. - dnl gnulib does not need it. But if it gets required by third-party macros - dnl after AC_USE_SYSTEM_EXTENSIONS is required, autoconf 2.62..2.63 emit a - dnl warning: "AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS". - dnl Note: We can do this only for one of the macros AC_AIX, AC_GNU_SOURCE, - dnl AC_MINIX. If people still use AC_AIX or AC_MINIX, they are out of luck. - m4_version_prereq([2.64], [], [AC_REQUIRE([AC_GNU_SOURCE])]) - AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS]) ])
