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Re: [PATCH] doc: mention how to set early defaults

From: Eric Blake
Subject: Re: [PATCH] doc: mention how to set early defaults
Date: Thu, 05 Sep 2013 14:49:24 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130805 Thunderbird/17.0.8

On 09/05/2013 02:20 PM, Eric Blake wrote:

> * doc/autoconf.texi (Diversion support) <m4_divert_text>: Add
> anchor.
> (External Software) <AC_ARG_WITH>: Demonstrate how to use DEFAULTS
> diversion, for earlier defaults.
> (Package Options) <AC_ARG_ENABLE>: Likewise.

> @@ -22111,7 +22118,7 @@ External Software
>    [AS_HELP_STRING([--with-readline],
>      [support fancy command line editing @@<:@@default=check@@:>@@])],
>    [],
> -  [with_readline=check])
> +  [m4_divert_text([DEFAULTS], [with_readline=check])])

And actually testing this reveals that autoconf generates a syntax error:

# Check whether --with-readline was given.
if test "${with_readline+set}" = set; then :


Looks like AS_IF doesn't know how to optimize out m4_divert_text as not
needing an else clause, so the example needs to be tweaked to provide an
explicit statement in argument 4 (':' will do), or use the
m4_divert_text outside of AC_ARG_WITH.  Another good reason why I posted
for review first rather than just pushing the patch.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library

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