Re: AS_IF optimization

[Ralf Wildenhues]

* Eric Blake wrote on Fri, Apr 10, 2009 at 07:11:45AM CEST:
> [moving to autoconf-patches]

[ dropping autoconf ]

> According to Eric Blake on 4/7/2009 7:13 AM:
> > According to Andreas Schwab on 4/7/2009 7:01 AM:
> >> According to <http://www.in-ulm.de/~mascheck/bourne/> this was fixed in
> >> the System III shell.
> >
> > Which pre-dates shell functions.  Therefore, since AS_IF is part of m4sh,
> > which guarantees a shell with functions, can elide empty else statements
> > with impunity.  Thanks for the research.
> 
> I'm thinking of applying this patch; any objections to the wording?

Can you hold back on this for a couple of days?  I'm still in the
process of going through Automake testsuite results, and might have
found a tangent issue.

Thanks,
Ralf

>  2009-04-09  Eric Blake  <address@hidden>
> 
> +     Improve documentation about if exit status.
> +     * doc/autoconf.texi (Limitations of Builtins) <if>: Mention that
> +     exit status bugs don't affect modern targets.
> +     Reported by Andreas Schwab.
> +
>       Make AS_IF, AS_CASE, and AS_FOR more robust to blank arguments.
>       * lib/m4sugar/m4sh.m4 (_AS_CASE, _AS_CASE_DEFAULT, AS_FOR, _AS_IF)
>       (_AS_IF_ELSE, AS_IF): Avoid syntax error on blank argument.
> diff --git a/doc/autoconf.texi b/doc/autoconf.texi
> index a47d3c8..c3033cd 100644
> --- a/doc/autoconf.texi
> +++ b/doc/autoconf.texi
> @@ -15829,7 +15829,8 @@ Limitations of Builtins
>  This is especially useful in other M4 macros, where the @dfn{then} and
>  @dfn{else} branches might be macro arguments.
> 
> -There are shells that do not reset the exit status from an @command{if}:
> +Some very old shells did not reset the exit status from an @command{if}
> +with no @command{else}:
> 
>  @example
>  $ @kbd{if (exit 42); then true; fi; echo $?}
> @@ -15837,9 +15838,10 @@ Limitations of Builtins
>  @end example
> 
>  @noindent
> -whereas a proper shell should have printed @samp{0}.  This is especially
> -bad in makefiles since it produces false failures.  This is why properly
> -written makefiles, such as Automake's, have such hairy constructs:
> +whereas a proper shell should have printed @samp{0}.  But this is no
> +longer a portability problem; any shell that supports functions gets it
> +correct.  However, it explains why some makefiles have such hairy
> +constructs:
> 
>  @example
>  if test -f "$file"; then