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Re: proposed gnulib-related additions to Autoconf

From: Gary V. Vaughan
Subject: Re: proposed gnulib-related additions to Autoconf
Date: Wed, 01 Mar 2006 20:39:44 +0000
User-agent: Mozilla Thunderbird 1.0.6 (Macintosh/20050716)

Hi Paul,

Paul Eggert wrote:
> "Gary V. Vaughan" <address@hidden> writes:
>>  i) Let's just improve AC_CHECK_HEADERS (et al) to always make configure
>>     smaller and faster by despatching to (undocumented internal)
>>     _AC_CHECK_HEADERS_ONCE when it can.
> Won't that break old scripts?  If they do something like this:
>   if test $ac_feature_foo = yes; then
>     AC_CHECK_HEADERS([sys/param.h])
>   fi
> then we'd hoist the test for sys/param.h out of the then-part, which
> is not what was intended.

Hmm.  You're right :-(  I was thinking that there might be a way to
detect from the argument signature of the call which flavour the user
wanted; but, looking at the implementation, the only way to do that
would be either an optional fifth argument (ugly), or perhaps if the
first argument does not end in `.h'.  The latter is really a motter
of picking between:


and, for example:

  AC_CHECK_HEADER([1], [sys/param.h])

On balance, the former is clearer.  Pity, as it adds just adds another
function that has to be supported in later releases :-(

>>  ii) I would have thought that use of shell functions in generated
>>     configure scripts is safe enough by now
> That's the direction I'd like to head too, but it's a big enough
> change that it will cause problems.  Let's wait until after 2.60 comes
> out.

Excellent.  Yes, I think it is more important to get a release soon so
that the huge improvements since 2.59 can begin to make their way to
developers that don't want to risk a CVS snapshot.

> It might make sense to have an "Autoconf 3" that has a lot of changes
> along these lines (I'd like to assume at least C89 and POSIX-2.1992
> conformance, for example; sheesh, it's 2006 already!), and reserve
> "Autoconf 2" for the current basic approach.

That sounds like the best way forward to me!

Gary V. Vaughan      ())_.  address@hidden,gnu.org}
Research Scientist   ( '/   http://tkd.kicks-ass.net
GNU Hacker           / )=   http://www.gnu.org/software/libtool
Technical Author   `(_~)_   http://sources.redhat.com/autobook

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