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Re: generated configure script doesn't work when "diff" isn't available

From: Ralf Wildenhues
Subject: Re: generated configure script doesn't work when "diff" isn't available
Date: Fri, 21 Mar 2008 01:41:10 +0100
User-agent: Mutt/1.5.17+20080114 (2008-01-14)

* Vincent Lefevre wrote on Thu, Mar 20, 2008 at 01:20:50AM CET:
> There would be another reason to use cmp instead of diff: it is
> simpler and lighter. So, why not using cmp and let the cygwin(?)
> developers fix their tools?

Because there is no fix.  cmp is working on binary files and diff
is working on text files, as designed.

FWIW, to make this discussion constructive, here's a quick and
incomplete patch to cope without diff in Autoconf (missing a NEWS
entry, documentation, and maybe a wrapper macro around $as_diff).
Vincent, it'd be nice if you could run the git Autoconf testsuite
on Maemo with this, to see if it stands a chance of working.

That's not to say that I'm sure I want this applied, but maybe it's
a better ground for discussion.

I don't like that this adds four forks to every configure invocation
but that's only a side issue.

The larger question is whether these systems are general enough to
warrant that Autoconf works on them.  AIUI since the Zaurus doesn't
have awk, the current git Autoconf won't work on it anyway.


2008-03-21  Ralf Wildenhues  <address@hidden>

        Port Autoconf to systems that lack 'diff'.
        * lib/m4sugar/m4sh.m4 (_AS_DIFF_PREPARE): New macro, sets
        as_diff to diff if present, otherwise cmp.
        (_AS_PREPARE): Call it.
        * lib/autoconf/general.m4 (AC_CACHE_SAVE): Use $as_diff.
        * lib/autoconf/programs.m4 (_AC_FEATURE_CHECK_LENGTH):
        * lib/autoconf/status.m4 (_AC_OUTPUT_HEADER): Likewise.
        * lib/autotest/general.m4 (AT_INIT): Initialize at_diff using
        Report by Vincent Lefevre.

diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
index 645108e..88df4f2 100644
--- a/lib/autoconf/general.m4
+++ b/lib/autoconf/general.m4
@@ -1943,7 +1943,7 @@ _AC_CACHE_DUMP() |
      t end
      :end'] >>confcache
-if diff "$cache_file" confcache >/dev/null 2>&1; then :; else
+if $as_diff "$cache_file" confcache >/dev/null 2>&1; then :; else
   if test -w "$cache_file"; then
     test "x$cache_file" != "x/dev/null" &&
       AC_MSG_NOTICE([updating cache $cache_file])
diff --git a/lib/autoconf/programs.m4 b/lib/autoconf/programs.m4
index 20fb479..674b2c2 100644
--- a/lib/autoconf/programs.m4
+++ b/lib/autoconf/programs.m4
@@ -509,7 +509,7 @@ m4_define([_AC_FEATURE_CHECK_LENGTH],
     cp "" ""
     AS_ECHO(['$4']) >> ""
     $3 < "" >"conftest.out" 2>/dev/null || break
-    diff "conftest.out" "" >/dev/null 2>&1 || break
+    $as_diff "conftest.out" "" >/dev/null 2>&1 || break
     ac_count=`expr $ac_count + 1`
     if test $ac_count -gt ${$1_max-0}; then
       # Best one so far, save it but keep looking for a better one
diff --git a/lib/autoconf/status.m4 b/lib/autoconf/status.m4
index c8f329a..ce9b068 100644
--- a/lib/autoconf/status.m4
+++ b/lib/autoconf/status.m4
@@ -669,7 +669,7 @@ which seems to be undefined.  Please make sure it is 
   esac \
   || AC_MSG_ERROR([could not create $ac_file])
 dnl This would break Makefile dependencies:
-dnl  if diff "$ac_file" "$tmp/out" >/dev/null 2>&1; then
+dnl  if $as_diff "$ac_file" "$tmp/out" >/dev/null 2>&1; then
 dnl    echo "$ac_file is unchanged"
 dnl  else
 dnl     rm -f "$ac_file"; mv "$tmp/out" "$ac_file"
@@ -864,7 +864,7 @@ m4_define([_AC_OUTPUT_HEADER],
       && eval '$AWK -f "$tmp/defines.awk"' "$ac_file_inputs"
     } >"$tmp/config.h" \
       || AC_MSG_ERROR([could not create $ac_file])
-    if diff "$ac_file" "$tmp/config.h" >/dev/null 2>&1; then
+    if $as_diff "$ac_file" "$tmp/config.h" >/dev/null 2>&1; then
       AC_MSG_NOTICE([$ac_file is unchanged])
       rm -f "$ac_file"
diff --git a/lib/autotest/general.m4 b/lib/autotest/general.m4
index c4cff41..e8b6192 100644
--- a/lib/autotest/general.m4
+++ b/lib/autotest/general.m4
@@ -928,7 +928,7 @@ test -d "$at_suite_dir" ||
   AS_ERROR([cannot create '$at_suite_dir'])
 # Can we diff with `/dev/null'?  DU 5.0 refuses.
-if diff /dev/null /dev/null >/dev/null 2>&1; then
+if $as_diff /dev/null /dev/null >/dev/null 2>&1; then
@@ -936,11 +936,11 @@ else
 # Use `diff -u' when possible.
-if at_diff=`diff -u "$at_devnull" "$at_devnull" 2>&1` && test -z "$at_diff"
+if at_diff=`$as_diff -u "$at_devnull" "$at_devnull" 2>&1` && test -z "$at_diff"
-  at_diff='diff -u'
+  at_diff="$as_diff -u"
-  at_diff=diff
+  at_diff=$as_diff
 # Get the last needed group.
diff --git a/lib/m4sugar/m4sh.m4 b/lib/m4sugar/m4sh.m4
index 8014f15..c351bdc 100644
--- a/lib/m4sugar/m4sh.m4
+++ b/lib/m4sugar/m4sh.m4
@@ -417,6 +417,7 @@ m4_defun([_AS_PREPARE],
 _AS_ECHO_N_PREPARE[]dnl We do not need this ourselves but user code might.
@@ -731,6 +732,19 @@ fi
+# ----------------
+# Maemo and the Zaurus do not have diff.  OTOH, we prefer diff
+# because it avoids spurious differences due to newline encoding.
+[if (diff $as_myself $as_myself) >/dev/null 2>&1; then
+  as_diff=diff
+  as_diff=cmp
 # ---------------------
 # Simulate the command 'dirname FILE-NAME'.  Not all systems have dirname.

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