Re: configuring sub directories optional

[Steve M. Robbins]

On Wed, Oct 30, 2002 at 12:12:20PM -0500, Eric Siegerman wrote:
> On Tue, Oct 29, 2002 at 07:16:45PM -0500, Steve M. Robbins wrote:
> > On Tue, Oct 29, 2002 at 01:52:20PM -0500, Stefan Seefeld wrote:
> > > AC_CONFIG_SUBDIRS(dirs, [action-if-succeeds], [action-if-fails])
> > > 
> > > is exactly what I had in mind.
> > 
> > If someone gets ambitious, it would be also useful to have
> > AC_CXX([action-if-succeeds],[action-if-fails]) to deal with
> > "compile-if-you-have-a-C++-compiler" bits of a package.
> 
> Assuming the AC_CONFIG_SUBDIRS enhancement is made,
> "compile-if-you-have-a-C++-compiler" should be implemented in
> terms of it, by putting the C++ code in a subpackage.

An interesting possibility that I hadn't considered.

The objection to this that some will have is that to require an extra
configure script and all that setup in a subdirectory is a heavy
burden for e.g. a single program or two that uses C++ in a large
package.  

To put this into a question: why should supporting optional C++ parts
of a package be so much more trouble than supporting an optional 3rd
party library?


> This will
> avoid a lot of rarely-used "[action-if-succeeds],
> [action-if-fails]" goo spreading throughout the API.
> 
> IMHO, adding such goo to AC_CONFIG_SUBDIRS is justified precisely
> because using subdirectories is a common and obvious way to
> factor out optional subcomponents of a package.  It's a single
> change that's sufficient to handle a wide set of similar cases.

I might be misremembering, but I seem to recall someone mooting
the possibility of wrapping macros like AC_CXX or AC_CONFIG_SUBDIRS
inside some (m4?) code that temporarily turns a fatal error into
a warning.  I think it did something like redefine AC_MSG_ERROR
into AC_MSG_WARN.  Does this ring any bells for someone?

-Steve