Re: Zsh 3 and ${1+"$@"} (Was: [GNU Autoconf 2.53] testsuite.log: 126 failures)

[Peter Stephenson <pws@csr.com>]

Akim Demaille wrote:
> Hi!
> 
> We (Autoconf) have a big problem with Zsh 3.0.8.  You know it is
> shipped on Darwin as /bin/sh.  But this version does not understand
> ${1+"$@"} properly.  We use this instead of "$@" to work around a bug
> which still exists today in many many constructors' /bin/sh, so we
> can't departure from it.

I think the problem you are running across is that with the option
SH_WORD_SPLIT set (as it is for sh compatibility), you get this behaviour:

% set 'one two'
% for arg in ${1+"$@"}; do echo $arg; done
one
two

whereas you expect `one two' on the same line.  This problem is still in
zsh 4 --- inside another substitution, either it's splitting all words
on spaces, or it's splitting none.

This sort of mess is why zsh doesn't have SH_WORD_SPLIT on by default,
but that doesn't help you...

If you want to work around this you have two basic choices:

1. Unset shwordsplit:
  [ x$ZSH_VERSION != x ] && unsetopt shwordsplit
This will have a knock on effect on all unquoted shell parameter
substitutions, however.  If you are relying on these producing multiple
command arguments --- e.g. for building up arguments for `for' loops in
a single parameter --- you are stuck unless you can find some way of
turning shwordsplit off and on before using ${1+"$@"}.  (Writers of
configure scripts --- not autoconf itself --- often incorrectly assume
something like `test x$foo != x' will always produce the same number of
words, but that's a separate problem from the one you face.)

2. Rework the substitution.  In zsh, you would get away with
${==1+"$@"}, since the doubled `=' is a flag to turn off SH_WORD_SPLIT
for that substitution.  Obviously, getting this in for zsh and not for
other shells is a bit of a nightmare.  Indeed, rather than do that, it
would presumably be easier to use "$@" for zsh instead of ${1+"$@"}
(this handles zero arguments correctly), which is exactly what you're
trying to avoid.

Neither of these looks very promising.

"${1+"$@"}" also works in zsh, but this confuses other variants of sh
--- it works in bash, but sh on SunOS 5.8 tripped over it.

I haven't looked for any cleverer substitutions which will always work.
Given that ${1+"$@"} is already a despairing workaround, it seems
unlikely there's anything more complicated which will fool everyone at
once.

-- 
Peter Stephenson <pws@csr.com>                  Software Engineer
CSR Ltd., Science Park, Milton Road,
Cambridge, CB4 0WH, UK                          Tel: +44 (0)1223 392070


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