m4_map_sep bug (introduced by 2005-06-06 Autoconf patch) breaks Bison

[Paul Eggert]

In <http://lists.gnu.org/archive/html/bug-bison/2005-10/msg00004.html>
"John P. Hartmann" <address@hidden> writes:

> http://lists.gnu.org/archive/html/autoconf-patches/2005-06/txtRXb8U1rojj.txt
> ... The change to m4sugar generates a spurious semicolon before the
> function body (opening {) when a function takes no parameters.
>
> This causes bison not to build.

Thanks for reporting this.  I have installed the following patch into
both GNU Autoconf and Bison, in an attempt to work around the problem.

Stepan, can you please double-check this patch?  It still feels
vaguely wrong.  I think that somehow m4_cdr is returning the empty
string rather than an empty list.  You can observe the effect of the
original bug by unpacking <ftp://ftp.gnu.org/gnu/bison/bison-2.1.tar.gz>
and looking at line 1235 of bison-2.1/src/parse-gram.c.  Thanks.

2005-10-05  Paul Eggert  <address@hidden>

        * lib/m4sugar/m4sugar.m4 (_m4_map): New macro.
        (m4_map, m4_map_sep): Use it.  Handle the empty list correctly.

--- lib/m4sugar/m4sugar.m4      25 Jul 2005 17:47:08 -0000      2.94
+++ lib/m4sugar/m4sugar.m4      5 Oct 2005 21:24:03 -0000
@@ -398,8 +398,11 @@ m4_define([m4_cdr],
 # of LIST (which can be lists themselves, for multiple arguments MACROs).
 m4_define([m4_fst], [$1])
 m4_define([m4_map],
+[m4_if([$2], [[]], [],
+       [_m4_map([$1], [$2])])])
+m4_define([_m4_map],
 [m4_ifval([$2],
-         [$1(m4_fst($2))[]m4_map([$1], m4_cdr($2))])])
+         [$1(m4_fst($2))[]_m4_map([$1], m4_cdr($2))])])
 
 
 # m4_map_sep(MACRO, SEPARATOR, LIST)
@@ -408,8 +411,8 @@ m4_define([m4_map],
 # are the elements of LIST (which can be lists themselves, for multiple
 # arguments MACROs).
 m4_define([m4_map_sep],
-[m4_ifval([$3],
-         [$1(m4_fst($3))[]m4_map([$2[]$1], m4_cdr($3))])])
+[m4_if([$3], [[]], [],
+       [$1(m4_fst($3))[]_m4_map([$2[]$1], m4_cdr($3))])])
 
 
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