Re: Fix chdir-long.m4 caching

[Eric Blake-1]

Hi Ralf,

> Hello Eric-1,  ;-)

I blame nabble for that.  Too bad that gmane doesn't know how to
let people reply nicely to cross-posted threads.

> > +# A little hack, as AT_CHECK_M4 already uses `stderr' to normalize it.
> > +AT_CHECK_AUTOCONF([2>&1], [], [stdout])
> > 
> > -    ' stderr]], [0],[$4])])
> > +    ' stderr >&2]], [0], [], [$4])])
> 
> This triggers the multiple redirection bug on Ultrix (see
> `(autoconf.info)File Descriptors'); I don't know if other, non-museum
> systems are affected, too.  But anyway we disallow it in the manual, so
> iff we decide that this is ok now, then at least both those doc parts
> need updates, too:

My patch is no worse than yours at violating this rule, and we already
violate it elsewhere in at least tests/torture.at.  Does anyone still have
access to Ultrix to see if there are some cases that work?  The example
in the manual only lists:

$ eval 'echo matter >fullness' >void
illegal io
$ eval '(echo matter >fullness)' >void
illegal io
$ (eval '(echo matter >fullness)') >void
Ambiguous output redirect.

but one could argue that the first two examples involve no
subshell, and in the third, because the subshell is invoking a shell
builtin with no unquoted metacharacters in the argument, that
Ultrix took a shortcut.  Maybe it would work correctly if the
two redirections of the same fd are in different levels of
subshells, with the inner not being a shell builtin?  Or is it
not worth worrying about, as this would only cause spurious
testsuite failures, but not impact autoconf proper?

-- 
Eric Blake-1
;)

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