expand-before-require bug

[Eric Blake]

As of this morning, autoconf.git now warns you on instances of expand-before-
require (aka ordering bugs in older autoconf, and redundant output when using 
bleeding edge autoconf).  I'm working on a series of patches to reduce the 
number of warnings we trigger, starting with this one:

configure.ac:33: warning: AC_REQUIRE: `AC_USE_SYSTEM_EXTENSIONS' was expanded 
before it was required
m4/extensions.m4:93: gl_USE_SYSTEM_EXTENSIONS is expanded from...
m4/gnulib-comp.m4:21: gl_EARLY is expanded from...
configure.ac:33: the top level
configure.ac:33: warning: AC_COMPILE_IFELSE was called before 
AC_USE_SYSTEM_EXTENSIONS
m4/extensions.m4:23: AC_USE_SYSTEM_EXTENSIONS is expanded from...
configure.ac:33: warning: AC_RUN_IFELSE was called before 
AC_USE_SYSTEM_EXTENSIONS

My analysis: gl_EARLY does the following:

  AC_REQUIRE([AC_GNU_SOURCE])
  AB_INIT
  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])

but AC_GNU_SOURCE expands, rather than requires, AC_USE_SYSTEM_EXTENSIONS, such 
that the later gl_USE_SYSTEM_EXTENSIONS, which requires 
AC_USE_SYSTEM_EXTENSIONS.  I can probably address some of this by changing 
AU_DEFUN in autoconf, such that autoupdate handles a macro differently than 
autoconf; but that will only affect autoconf 2.64+.  For autoconf 2.63, this 
means that we truly have an out-of-order expansion situation.  For even earlier 
autoconf, such as 2.59, AC_GNU_SOURCE did not require AC_USE_SYSTEM_EXTENSIONS, 
so there is no ordering dependency there; however, gnulib ALREADY provides a 
working AC_USE_SYSTEM_EXTENSIONS, even for autoconf 2.59.  Therefore, I see no 
reason for us to even worry about using AC_GNU_SOURCE.

Besides, the only use of AC_GNU_SOURCE in current gnulib sources is in 
m4/threadlib.m4, but that is from gettext, and is already coded to use 
AC_GNU_SOURCE only if AC_USE_SYSTEM_EXTENSIONS is not available, because Bruno 
didn't want that file to suck in gl_USE_SYSTEM_EXTENSIONS.

Therefore, I'm committing this patch (I love it when pure deletion fixes a bug, 
and makes gnulib-tool fork fewer times to boot):


From: Eric Blake <address@hidden>
Date: Wed, 21 Jan 2009 09:55:55 -0700
Subject: [PATCH] gnulib-tool: avoid warnings from using obsolete AC_GNU_SOURCE

* gnulib-tool (func_dest_tmpfilename, func_create_testdir): Using
obsolete AC_GNU_SOURCE causes out-of-order expansion; avoid it,
and rely solely on gl_USE_SYSTEM_EXTENSIONS.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog   |    7 +++++++
 gnulib-tool |   11 -----------
 2 files changed, 7 insertions(+), 11 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index af6bee5..7b7c8bd 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+2009-01-21  Eric Blake  <address@hidden>
+
+       gnulib-tool: avoid warnings from using obsolete AC_GNU_SOURCE
+       * gnulib-tool (func_dest_tmpfilename, func_create_testdir): Using
+       obsolete AC_GNU_SOURCE causes out-of-order expansion; avoid it,
+       and rely solely on gl_USE_SYSTEM_EXTENSIONS.
+
 2009-01-21  Paolo Bonzini  <address@hidden>
 
        Revert:
diff --git a/gnulib-tool b/gnulib-tool
index c11ef35..c6725d3 100755
--- a/gnulib-tool
+++ b/gnulib-tool
@@ -3378,9 +3378,6 @@ s,//*$,/,'
     if test -n "$uses_subdirs"; then
       echo "  AC_REQUIRE([AM_PROG_CC_C_O])"
     fi
-    if grep AC_GNU_SOURCE "$destdir"/$m4base/*.m4 >/dev/null 2>/dev/null; then
-      echo "  AC_REQUIRE([AC_GNU_SOURCE])"
-    fi
     for module in $final_modules; do
       func_verify_module
       if test -n "$module"; then
@@ -3919,10 +3916,6 @@ func_create_testdir ()
      echo "AC_PROG_MAKE_SET"
      echo "AC_PROG_RANLIB"
      echo
-     if grep AC_GNU_SOURCE "$testdir/$m4base"/*.m4 >/dev/null 2>/dev/null; then
-       echo "AC_GNU_SOURCE"
-       echo
-     fi
      for module in $modules; do
        func_verify_module
        if test -n "$module"; then
@@ -4052,10 +4045,6 @@ func_create_testdir ()
      echo "AM_PROG_CC_C_O"
      echo
    fi
-   if grep AC_GNU_SOURCE "$testdir/$m4base"/*.m4 >/dev/null 2>/dev/null; then
-     echo "AC_GNU_SOURCE"
-     echo
-   fi
    for module in $modules; do
      func_verify_nontests_module
      if test -n "$module"; then
-- 
1.6.0.4