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Re: Empty else part in AS_IF

From: Julien ÉLIE
Subject: Re: Empty else part in AS_IF
Date: Wed, 09 Oct 2013 21:47:46 +0200
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.8; rv:17.0) Gecko/20130801 Thunderbird/17.0.8

Hi Eric,

First of all, thanks for your answer.

  AS_IF([test x"$var" != xfalse],
          [AM_CONDITIONAL([TEST], [false])])])

gives the following configure code with autoconf 2.69:

  if test x"$var" != xfalse; then :

That's unusual shell syntax (it does NOT do a variable assignment; did
you mean 'test=1' instead of trying to execute the program whose name is
the expansion of $test concatenated with '=1'?)

Yes, you're right.  I meant to write "test=1" in the provided sample.
We have a far more complex m4 file (used for INN, a news server), and I just wanted to provide a minimal AS_IF to explain what I was facing.

It is the reason why the error I quoted from configure is at line 23581 :)

./configure: line 23581: syntax error near unexpected token `fi'
./configure: line 23581: `fi'



which is not a valid syntax.

Indeed.  The problem is that autoconf cannot tell if a non-empty literal
will expand to empty text (m4_ifdef results in no output).  You'll have
to workaround it yourself:

AS_IF([test x"$var" != xfalse],
     [: m4_ifdef(...)])

Thanks for the suggestion of [: m4_ifdef(...)]. It looks prettier than adding [:] in the arguments of m4_ifdef.

Have a nice week,

Julien ÉLIE

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