Re: Rejecting dash because it lacks +=?

[Eric Blake]

Paolo Bonzini <bonzini <at> gnu.org> writes:

> 2) The AS_VAR_APPEND technique, right now, does not give any speedup in
> Autoconf-generated scripts, as far as I could read.

It depends on how many appends are taking place.  It matters more for coreutils 
than m4, for example, because coreutils generates a longer as_func_list based 
on its use of AC_CHECK_FUNCS_ONCE.

>  Nevertheless, we
> are rejecting all shells that do not support +=.  This, unlike LINENO,
> is a pity, because it means that for everybody who's not using bash or
> zsh, but has it installed, the scripts will rerun in bash or zsh.  This
> means in turn that we get much less coverage of shells in the wild.

POSIX requires $LINENO (dash is buggy for not providing it).  It does not 
require +=.  So, I can agree with your reluctance on rejecting shells that do 
not provide POSIX extensions.  How about a patch to AS_VAR_APPEND that removes 
the _AS_DETECT_SUGGESTED line, along with a policy that M4sh will never 
_AS_DETECT a non-POSIX feature?  (M4sh clients could still suggest non-POSIX 
extensions, if we were to ever export and document a public version of 
_AS_DETECT_*, but that would be their choice to omit dash support, and not 
forced on them by M4sh.)

I'm committing this:

>From 5184bb08838be30118ac26710a1f31bb673c062f Mon Sep 17 00:00:00 2001
From: Eric Blake <address@hidden>
Date: Thu, 30 Oct 2008 09:39:57 -0600
Subject: [PATCH] Don't check for non-POSIX extensions in suggested tests.

* lib/m4sugar/m4sh.m4 (_AS_VAR_APPEND_WORKS): Remove suggestion;
we still use += if available, but should not reject shells that
don't provide it.
(_AS_DETECT_SUGGESTED): Document a policy for m4sh.

Signed-off-by: Eric Blake <address@hidden>
---
 ChangeLog           |    8 ++++++++
 lib/m4sugar/m4sh.m4 |    7 ++++++-
 2 files changed, 14 insertions(+), 1 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index e19a3f6..914f83b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,13 @@
 2008-10-30  Eric Blake  <address@hidden>
 
+       Don't check for non-POSIX extensions in suggested tests.
+       * lib/m4sugar/m4sh.m4 (_AS_VAR_APPEND_WORKS): Remove suggestion;
+       we still use += if available, but should not reject shells that
+       don't provide it.
+       (_AS_DETECT_SUGGESTED): Document a policy for m4sh.
+
+2008-10-30  Eric Blake  <address@hidden>
+
        Work around Solaris /bin/sh case bug.
        * lib/m4sugar/m4sh.m4 (_AS_CASE, _AS_CASE_DEFAULT): Always provide
        a non-empty command list.
diff --git a/lib/m4sugar/m4sh.m4 b/lib/m4sugar/m4sh.m4
index 1f1f599..bf18235 100644
--- a/lib/m4sugar/m4sh.m4
+++ b/lib/m4sugar/m4sh.m4
@@ -173,6 +173,9 @@ m4_define([_AS_DETECT_EXPAND],
 # -------------------------
 # Refuse to execute under a shell that does not pass the given TEST.
 # Does not do AS_REQUIRE for the better-shell detection code.
+#
+# M4sh should never require something not required by POSIX, although
+# other clients are free to do so.
 m4_defun([_AS_DETECT_REQUIRED],
 [m4_set_add([_AS_DETECT_REQUIRED_BODY], [$1 || AS_EXIT])])
 
@@ -181,6 +184,9 @@ m4_defun([_AS_DETECT_REQUIRED],
 # --------------------------
 # Prefer to execute under a shell that passes the given TEST.
 # Does not do AS_REQUIRE for the better-shell detection code.
+#
+# M4sh should never suggest something not required by POSIX, although
+# other clients are free to do so.
 m4_defun([_AS_DETECT_SUGGESTED],
 [m4_set_add([_AS_DETECT_SUGGESTED_BODY], [$1 || AS_EXIT])])
 
@@ -1679,7 +1685,6 @@ m4_define([_AS_VAR_APPEND_WORKS],
 # Note that unlike AS_VAR_SET, VALUE must be properly quoted to avoid
 # field splitting and file name expansion.
 m4_defun_init([AS_VAR_APPEND],
-[_AS_DETECT_SUGGESTED([_AS_VAR_APPEND_WORKS])]dnl
 [AS_REQUIRE([_AS_VAR_APPEND_PREPARE], [], [M4SH-INIT-FN])],
 [as_func_append $1 $2])
 
-- 
1.6.0.2