1 files changed, 18 insertions, 4 deletions

diff --git a/gl/m4/extensions.m4 b/gl/m4/extensions.m4
index ba6d5e19..7d9458a8 100644
--- a/gl/m4/extensions.m4
+++ b/gl/m4/extensions.m4
@@ -1,7 +1,7 @@
-# serial 8  -*- Autoconf -*-
+# serial 9  -*- Autoconf -*-
 # Enable extensions on systems that normally disable them.
 
-# Copyright (C) 2003, 2006-2009 Free Software Foundation, Inc.
+# Copyright (C) 2003, 2006-2010 Free Software Foundation, Inc.
 # This file is free software; the Free Software Foundation
 # gives unlimited permission to copy and/or distribute it,
 # with or without modifications, as long as this notice is preserved.
@@ -12,6 +12,20 @@
 # enough in this area it's likely we'll need to redefine
 # AC_USE_SYSTEM_EXTENSIONS for quite some time.
 
+# If autoconf reports a warning
+#     warning: AC_COMPILE_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS
+# or  warning: AC_RUN_IFELSE was called before AC_USE_SYSTEM_EXTENSIONS
+# the fix is
+#   1) to ensure that AC_USE_SYSTEM_EXTENSIONS is never directly invoked
+#      but always AC_REQUIREd,
+#   2) to ensure that for each occurrence of
+#        AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
+#      or
+#        AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+#      the corresponding gnulib module description has 'extensions' among
+#      its dependencies. This will ensure that the gl_USE_SYSTEM_EXTENSIONS
+#      invocation occurs in gl_EARLY, not in gl_INIT.
+
 # AC_USE_SYSTEM_EXTENSIONS
 # ------------------------
 # Enable extensions on systems that normally disable them,
@@ -74,8 +88,8 @@ AC_BEFORE([$0], [AC_RUN_IFELSE])dnl
     [ac_cv_safe_to_define___extensions__],
     [AC_COMPILE_IFELSE(
        [AC_LANG_PROGRAM([[
-#         define __EXTENSIONS__ 1
-          ]AC_INCLUDES_DEFAULT])],
+#         define __EXTENSIONS__ 1
+          ]AC_INCLUDES_DEFAULT])],
        [ac_cv_safe_to_define___extensions__=yes],
        [ac_cv_safe_to_define___extensions__=no])])
   test $ac_cv_safe_to_define___extensions__ = yes &&