Improve M4 path searching during configure.

* lib/autoconf/programs.m4 (AC_PATH_PROGS_FEATURE_CHECK): New
macro.
(_AC_PATH_PROG_FEATURE_CHECK): Rename...
(_AC_PATH_PROGS_FEATURE_CHECK): ...to this, add defaulted action
parameter, and kill side effects.
(_AC_PROG_GREP, AC_PROG_SED): Adjust callers.
(_AC_FEATURE_CHECK_LENGTH): Kill extra whitespace.
* m4/m4.m4 (AC_PROG_GNU_M4): Don't stop searching until working m4
is found.
(AC_PATH_PROGS_FEATURE_CHECK): Add backwards compatibility hack to
allow bootstrapping with autoconf 2.61.
* configure.ac (M4): AC_PROG_GNU_M4 now exits on failure.
* configure: Regenerate.
* doc/autoconf.texi (Generic Programs): Document new macro.
* tests/mktests.sh (au_exclude_script): Exclude auto-testing new
macro.
* tests/semantics.at (AC_PATH_PROGS_FEATURE_CHECK): New test.
* NEWS: Document the change.
* THANKS: Update.
Reported by Hans Aberg.

1 files changed, 25 insertions, 16 deletions

diff --git a/m4/m4.m4 b/m4/m4.m4
index 70b99f89..70f30767 100644
--- a/m4/m4.m4
+++ b/m4/m4.m4
@@ -1,4 +1,4 @@
-# m4.m4 serial 3
+# m4.m4 serial 4
 dnl Copyright (C) 2000, 2006, 2007 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -12,20 +12,29 @@ dnl with or without modifications, as long as this notice is preserved.
 # Also, check whether --error-output (through 1.4.x) or --debugfile (2.0)
 # is supported, and AC_SUBST M4_DEBUGFILE accordingly.
 AC_DEFUN([AC_PROG_GNU_M4],
-[AC_PATH_PROGS([M4], [gm4 gnum4 m4], [m4])
-AC_CACHE_CHECK([whether m4 supports accurate traces], [ac_cv_prog_gnu_m4],
-[ac_cv_prog_gnu_m4=no
-dnl Creative quoting here to avoid raw dnl and ifdef in configure.
-if test x"$M4" != x \
-    && test -z "`echo if'def(mac,bug)d'nl | $M4 --trace=mac 2>&1`" ; then
-  ac_cv_prog_gnu_m4=yes
-fi])
-if test $ac_cv_prog_gnu_m4 = yes ; then
+  [AC_ARG_VAR([M4], [Location of GNU M4 1.4.5 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],
+    [AC_PATH_PROGS_FEATURE_CHECK([M4], [m4 gm4 gnum4],
+      [dnl Creative quoting here to avoid raw dnl and ifdef in configure.
+      test -z "`echo if'def(mac,bug)d'nl | $ac_path_M4 --trace=mac 2>&1`" \
+      && ac_cv_path_M4=$ac_path_M4 ac_path_M4_found=:],
+      [AC_MSG_ERROR([no acceptable m4 could be found in \$PATH.
+GNU M4 1.4.5 or later is required; 1.4.8 is recommended])])])
+  M4=$ac_cv_path_M4
   AC_CACHE_CHECK([how m4 supports trace files], [ac_cv_prog_gnu_m4_debugfile],
-  [case `$M4 --help < /dev/null 2>&1` in
-    *debugfile*) ac_cv_prog_gnu_m4_debugfile=--debugfile ;;
-    *) ac_cv_prog_gnu_m4_debugfile=--error-output ;;
-  esac])
-  AC_SUBST([M4_DEBUGFILE], $ac_cv_prog_gnu_m4_debugfile)
-fi
+    [case `$M4 --help < /dev/null 2>&1` in
+      *debugfile*) ac_cv_prog_gnu_m4_debugfile=--debugfile ;;
+      *) ac_cv_prog_gnu_m4_debugfile=--error-output ;;
+    esac])
+  AC_SUBST([M4_DEBUGFILE], [$ac_cv_prog_gnu_m4_debugfile])
 ])
+
+# Compatibility for bootstrapping with Autoconf 2.61.
+dnl FIXME - replace this with AC_PREREQ([2.62]) after the release.
+# AC_PATH_PROGS_FEATURE_CHECK was added the same time the slightly broken,
+# undocumented _AC_PATH_PROG_FEATURE_CHECK was deleted.
+m4_ifndef([AC_PATH_PROGS_FEATURE_CHECK],
+  [m4_define([AC_PATH_PROGS_FEATURE_CHECK],
+    [_AC_PATH_PROG_FEATURE_CHECK([$1], [$2], [$3], [$5])
+])])