Re: AC_CONFIG_SUBDIRS

[Ralf Wildenhues]

Hello Bob,

* Bob Rossi wrote on Wed, Dec 06, 2006 at 03:40:00PM CET:
> 
> When you run the top-level configure script, it determines what libraries you 
> need to build the project, and then downloads the .tar.gz dependency, untars
> it, and configures it. Currently I ./configure the sub projects manually by
> calling the sub projects ./configure directly. However, using 
> AC_CONFIG_SUBDIRS 
> might be better, because I think it'll pass down the top-level configure 
> options 
> to the subproject.

Right.  It assumes some things though: for example, that you may want to
share the cache file between the two configure runs.  This is not
practical, for example, if one but not both packages are to be cross
compiled (e.g., because you need a compiler for both $host and $build).

> I'm wondering if there is a way to get AC_CONFIG_SUBDIRS to work, even
> though the configure script or sub directory isn't available until
> ./configure is run and it determines what libraries to download. 

This should already work out of the box.  If the file $sub/configure is
present at the time it should be run (at the end of configuring), then
it will be run.

> I'm wondering how options are passed down through AC_CONFIG_SUBDIRS from
> the top-level Makefile. Can you tweak the options for each sub project?

No.  This is currently one of the biggest limitations of this macro.
I'd be happy if we could come up with another macro for sub-configure
scripts that would allow for more freedom.  Primary issues are:
- What and how can we allow the user to specify what is passed/mangled/
  not passed?  This is trickier than it seems: package authors typically
  cannot know which option an end-user would like to be passed down.
- When should cache file sharing be turned off?

Some other technical details come to mind as well.

This could help eliminate the number of mostly-buggy hand-written bits
that several package use, in the long term.

If you embark upon writing a private macro for yourself, please start
from a recent copy of Autoconf's and modify that.  Older versions have
had more quoting quirks.

Cheers,
Ralf