Require GNU M4 1.4.8 or later.

The former minimum version was 1.4.6.  1.4.6 and 1.4.7 do not track
the original location of text fed to ‘m4wrap’, which breaks autom4te’s
ability to trace macros invoked from _AC_FINALIZE.

Right now, the only _user_ visible effect of this is that autoconf
running on M4 1.4.6 or 1.4.7 will emit an internal error, instead of
the intended warning message, when it processes a configure.ac that
neglects to invoke AC_INIT or AC_OUTPUT.  Perhaps more importantly,
it causes a bunch of scary-sounding failures in our own testsuite,
which deliberately doesn’t use AC_OUTPUT sometimes.

M4 1.4.6 and 1.4.7 also have bugs in location tracking of macro
invocations spread over multiple lines, which, guess what, causes
even more testsuite failures.

1.4.8 came out in 2006.  As a practical matter, this change to our
requirements means that people using macOS *to run autoconf* (not just
to run generated configure scripts) cannot use the system-provided m4
anymore.  {Free,Net,Open}BSD already don’t ship GNU M4 as their system
m4, so users of those OSes should not be affected.

diff --git a/NEWS b/NEWS
index 4e41345df8dd6d033d2840ff77661179a5ab0d0c..91164390717459d86af81de97328393ca3a0dc80 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -7,6 +7,20 @@ GNU Autoconf NEWS - User visible changes.
 *** Autoconf now requires perl 5.8 (2002) or later.
   Generated 'configure' scripts continue to run without perl.
 
+*** Autoconf now requires GNU M4 1.4.8 (2006) or later.
+  Generated 'configure' scripts continue to run without M4.
+
+  Use of GNU M4 1.4.16 or later is recommended, as all earlier versions
+  are known to have had serious bugs in the text-processing builtins
+  on some, but not all, operating systems.  Autoconf’s own configure
+  script will attempt to find a version of M4 that is not affected by
+  these bugs.
+
+  Note: Autoconf 2.70 and 2.71 include code that malfunctions with
+  M4 1.4.6 or 1.4.7.  However, the only effect of the malfunction is
+  that you will get a confusing error message if you run autoconf on
+  a configure.ac that neglects to use AC_INIT or AC_OUTPUT.
+
 ** New features
 ** Obsolete features and new warnings
 

diff --git a/m4/m4.m4 b/m4/m4.m4
index 0fedaca89d2a96aff136c7f2ae5abf30c4876645..66e7341f0c4ed38ba7682d07d915b0c8a4258ffd 100644 (file)
--- a/m4/m4.m4
+++ b/m4/m4.m4
@@ -10,7 +10,7 @@
 
 # AC_PROG_GNU_M4
 # --------------
-# Check for GNU M4, at least 1.4.6 (all earlier versions had bugs in
+# Check for GNU M4, at least 1.4.8 (all earlier versions had bugs in
 # trace support and regexp support):
 # https://lists.gnu.org/archive/html/bug-gnu-utils/2006-11/msg00096.html
 # https://lists.gnu.org/archive/html/bug-autoconf/2009-07/msg00023.html
@@ -18,7 +18,7 @@
 # is supported, and AC_SUBST M4_DEBUGFILE accordingly.
 # Also avoid versions of m4 that trigger strstr bugs.
 AC_DEFUN([AC_PROG_GNU_M4],
-  [AC_ARG_VAR([M4], [Location of GNU M4 1.4.6 or later.  Defaults to the first
+  [AC_ARG_VAR([M4], [Location of GNU M4 1.4.8 or later.  Defaults to the first
     program of 'm4', 'gm4', or 'gnum4' on PATH that meets Autoconf needs.])
   AC_CACHE_CHECK([for GNU M4 that supports accurate traces], [ac_cv_path_M4],
     [rm -f conftest.m4f
@@ -36,13 +36,21 @@ AC_PATH_PROGS_FEATURE_CHECK([M4], [m4 gm4 gnum4],
       ac_snippet=${ac_snippet}${as_nl}if'else(in''dex(dnl
 ;:11-:12-:12-:12-:12-:12-:12-:12-:12.:12.:12.:12.:12.:12.:12.:12.:12-,dnl
 :12-:12-:12-:12-:12-:12-:12-:12-),-1,,strstr-bug2)'
+      # Root out M4 1.4.6 and 1.4.7, which do not implement --debug=aflq
+      # correctly for macros invoked from m4wrap.
+      ac_snip2=change'quote(<,>)def''ine(<T>,<>)d'nl
+      ac_snip2=${ac_snip2}${as_nl}def'ine(<F>,<T(<traced>)>)d'nl
+      ac_snip2=${ac_snip2}${as_nl}m4'wrap(<F>)d'nl
       test -z "`$ac_path_M4 -F conftest.m4f </dev/null 2>&1`" \
       && test -z "`AS_ECHO([$ac_snippet]) | $ac_path_M4 --trace=mac 2>&1`" \
       && test -f conftest.m4f \
+      && test x"`AS_ECHO([$ac_snip2]) | \
+                $ac_path_M4 --trace=T --debug=aflq 2>&1`" = \
+              x'm4trace:stdin:3: -1- T(<traced>)' \
       && ac_cv_path_M4=$ac_path_M4 ac_path_M4_found=:
       rm -f conftest.m4f],
       [AC_MSG_ERROR([no acceptable m4 could be found in \$PATH.
-GNU M4 1.4.6 or later is required; 1.4.16 or newer is recommended.
+GNU M4 1.4.8 or later is required; 1.4.16 or newer is recommended.
 GNU M4 1.4.15 uses a buggy replacement strstr on some systems.
 Glibc 2.9 - 2.12 and GNU M4 1.4.11 - 1.4.15 have another strstr bug.])])])
   M4=$ac_cv_path_M4