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Re: AM_CONDITIONAL fails with line break at the end of $2

From: Eric Blake
Subject: Re: AM_CONDITIONAL fails with line break at the end of $2
Date: Thu, 17 Jul 2014 12:54:06 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0

On 07/17/2014 12:44 PM, Dimitrios Apostolou wrote:
> Hi Erik, thank you for forwarding to the appropriate list!
> On Thu, 17 Jul 2014, Eric Blake wrote:
>> I don't know if automake should work around your bad syntax, or if you
>> should just fix your to use correct syntax to begin with. I
> Is my syntax illegal? Can't I put line-breaks there? If I knew I
> wouldn't bother with this patch, it's just that I consumed some time to
> figure out this failure, so I thought it would be helpful to others.

Not illegal (there's no law prohibiting it), but not typical; and the
fact that it is causing a syntax error is a sign that fixing your code
is more likely to bring it in line with other packages, than waiting for
the tools to be taught to work with your usage as a new pattern, and
then waiting for that fix to percolate to the distros you care about.

More typical usage looks like one of these:

    [test "x$with_libxml2" != xno &&
     test "x$ac_cv_lib_xml2_xmlFirstElementChild" = xyes])


    test "x$with_libxml2" != xno &&
    test "x$ac_cv_lib_xml2_xmlFirstElementChild" = xyes]dnl

(that is, you'll usually see the close ) flush against the close ], or
you will see a use of 'dnl' to eat any newlines that were used to
visually spot that the closing ) on the start of the next line matches
an earlier line above)

>> also wonder if automake could use AS_IF instead of open-coding the if to
>> try and take advantage of autoconf's smarts for trying to sanitize
>> conditions.
>> However, even autoconf's AS_IF current implementation prefers the 'if
>> cond; then' rather than 'if cond $newline then', so it is likewise not
>> robust to conditions ending in a spurious newline.  If changing AS_IF to
>> use newline separator does not increase configure size, I could see
>> making that change in autoconf.  I'll play with the idea.
> Thanks, please keep me posted!


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

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