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Re: how to check that TidyLib is new enough?

From: Brian Dessent
Subject: Re: how to check that TidyLib is new enough?
Date: Sat, 06 Sep 2008 14:12:16 -0700

Jack Bates wrote:

> This module builds against TidyLib, so I use AC_CHECK_HEADER() to check
> for buffio.h, and checkout the TidyLib source code from SourceForge
> using CVS if it is not found:

Oh, this is evil and horrible:

CPPFLAGS="$CPPFLAGS -I/usr/include/tidy"
AC_CHECK_HEADER([buffio.h], [
], [

  AC_MSG_NOTICE([Fetching TidyLib...])
  cvs -z3 -d:pserver:address@hidden:/cvsroot/tidy co
-P tidy
  (cd tidy; sh build/gnuauto/

  CPPFLAGS="$CPPFLAGS -I\$(top_srcdir)/tidy/include"
  MODULE_LDFLAGS="$MODULE_LDFLAGS \$(top_srcdir)/tidy/src/*.lo"

There are so many things wrong with this: It's evil to assume the
library is installed in /usr/include.  This breaks the ability to use a
non-system version of the lib.  It also breaks cross compilation. 
Moreover, automatically checking something out of CVS is questionable
behavior for running a configure script.  Give the user a pointer as to
what's required in an error message if you want.

The proper way to handle this is to accept --with-tidylib= (see
AC_ARG_WITH), and then adds -I$with_tidylib/include/tidy to CPPFLAGS and
-L$with_tidylib/lib to LDFLAGS.  You can default the value to /usr if it
is not set or equals yes, if you want.

> What is the "correct" way to use autoconf to check that version of
> TidyLib it finds is new enough?

You write checks that test the specific things you are interested in. 
So, for example you write an AC_TRY_COMPILE that tries to use type
TidyAllocator and if it fails you either disable tidylib support (if
it's optional) or print an error message that says the version is too


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