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Re: expand-before-require bug

From: Paolo Bonzini
Subject: Re: expand-before-require bug
Date: Fri, 23 Jan 2009 13:06:06 +0100
User-agent: Thunderbird (Macintosh/20081209)

Bruno Haible wrote:
> Paolo Bonzini wrote:
>>>   - macros defined with AC_DEFUN_IDEMPOTENT are *known* to be expandable
>>>     any number of times, hence they may be both invoked and required,
>>>   - macros defined with AC_DEFUN_ONCE are *known* to be expandable only
>>>     once, hence the recommendation for them is to AC_REQUIRE them,
>> Do we have any of these?  I'd just change AC_DEFUN_ONCE to the meaning
>> you suggest for AC_DEFUN_IDEMPOTENT
> It's too late for doing that: AC_DEFUN_ONCE was introduced on 2004-10-11.

I know.

> Besides that, AC_DEFUN_ONCE and AC_DEFUN_IDEMPOTENT have really opposite
> semantics. You cannot confuse people more than by using the same name for
> two entities with opposite semantics.

It looks to me like, in the wild, AC_DEFUN_ONCE is used for idempotent
macros (and in Autoconf too, see AC_CANONICAL_*).  The only correct use
of AC_DEFUN_ONCE (where the warning *is* desired) is AC_NO_EXECUTABLES;
and not even fully correct, as you'd want an error there.

You can look at all of them at



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