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Re: Using AM_CONDITIONAL in m4 macros

From: Stefano Lattarini
Subject: Re: Using AM_CONDITIONAL in m4 macros
Date: Fri, 18 Jan 2013 22:58:35 +0100

On 01/18/2013 07:45 PM, Philipp Thomas wrote:
> * Nick Bowler (address@hidden) [20130118 17:17]:
>> If the package author(s) provided a script to bootstrap the build
>> system, then you should use that script.  Someone made the effort to
>> write that script, and they presumably did not do so for no reason.
> I have no idea why they originally wrote that script. Fact is it failed to
> update the libtool configury correctly so that builing failed because of
> libtool version mismatches. I had (wrongly) assumed that running autoreconf 
> instead would get me quicker to a building package.
>> You say that the provided script works, so that implies that a plain
>> autoreconf is not the correct way to bootstrap this package.
> That wasn't quite correct as I wrote above.
>> If you think this is a bug or limitation in autoreconf, could you
>> provide a small example package which demonstrates the problem?
> ATM I have no time for dol an example package but the scenario I encounterd
> goes something like this:
> In file swig.m4:
>    if test ! -z "$has_swig"; then
>         SWIG_LIB=`$SWIG -swiglib`
>         AM_CONDITIONAL(HAS_SWIG,[test 1])
>    else
>         AM_CONDITIONAL(HAS_SWIG,[test 0])
>    fi
> ])
This is a user error; according to the POSIX standard, "test N"
evaluates to "true" for every N >= 0:

  $ bash -c 'test 1' && echo TRUE
  $ bash -c 'test 0' && echo TRUE
  $ dash -c 'test 1' && echo TRUE
  $ dash -c 'test 0' && echo TRUE

A correct usage would probably be something like (untested):

   AM_CONDITIONAL([HAS_SWIG], [test x"$has_swig" != x])
   test x"$has_swig" != x && SWIG_LIB=`$SWIG -swiglib`

> And autoreconf complains that there is no AM_CONDITIONAL for HAS_SWIG
> unless I directly m4_include swig.m4. Is that a suffient description?
As for this, it might be a bug or a limitation, since it doesn't seem
related to the user error above.  Could you try to send a minimal and
correct reproducer for it?


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