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Re: ac_top_srcdir not set

From: Christian Cornelssen
Subject: Re: ac_top_srcdir not set
Date: Thu, 20 Feb 2003 16:15:26 +0100 (CET)


On Wed, 19 Feb 2003, Pavel Roskin wrote:

> Autoconf 2.57 as well as CVS autoconf doesn't set ac_top_srcdir and
> several other variables in packages with just one

Well, I guess it's used on an "as needed" basis: Whoever needs a valid
$ac_top_srcdir calls _AC_SRCPATHS for that.  To me it seems that
_AC_SRCPATHS is mainly used for `config.status' fragments.  If you
need it in your `' then I'd recommend calling _AC_SRCPATHS

> The reason is because _AC_SRCPATHS is only used in general.m4 like this:

... and in `status.m4' for CONFIG_COMMANDS fragments written to

> _AC_SRCPATHS is the only place where ac_top_srcdir is set.  ac_top_srcdir
> is documented and there is no mention that it may not be set under certain
> conditions.

Do you mean the node "Preset Output Variables"?  If so, this does not
imply that these are valid within `'.

> What's even worth, we may have some variables like ac_srcdir left from the
> last subdirectory.

As long as updates are not needed by the Autoconf macros, that's OK I
guess.  And the Autoconf macros call _AC_SRCPATHS when needed.

> It appears that the error messages reported by Christian Cornelssen in
> may be a result of ac_srcdir not being set.

Not really.  The error messages resulted from _AC_SRCPATHS being
called (and improperly assuming that for every build subdir there is a
corresponding src subdir), not from _AC_SRCPATHS being _not_ called.

> Following patch fixes the problem.  It has been tested both for local and
> srcdir builds.  I haven't worked on Autoconf for some time, so I need
> somebody to look at this patch to make sure that I'm not doing anything
> stupid.
> --- lib/autoconf/general.m4
> +++ lib/autoconf/general.m4
> @@ -1067,6 +1067,8 @@
>    done
>  fi
> +_AC_SRCPATHS(["."])
> +
>  test -n "$ac_init_help" && exit 0
>  m4_divert_pop([HELP_END])dnl
>  ])# _AC_INIT_HELP

I'm not an Autoconf wizard and cannot approve this.  The patch looks
harmless, but actually every cd would invalidate the variables set by
the latest _AC_SRCPATHS call, and there would be quite a lot of cds in
the Autoconf macro definitions to check (at least those which cd and
subsequently use user-supplied stuff.)  Therefore I'd rather suggest
clarifying that certain output variables need not be valid for the
actual "configure" run, and perhaps specifying macros to get them set


Christian Cornelssen

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