Samba 4 build system - more thoughts on scons

[Jelmer Vernooij]

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Hi,

The Samba 4 build system is getting more and more enhanced. We
originally started out with a traditional autoconf system. I.e. we
generated a configure script from configure.in that then substituted
several values in Makefile.in.

Metze and I have gradually been changing this to an autogenerated
Makefile. We just abandoned the templating mechanism and are now
generating the Makefile directly from the data gathered by configure
and various .mk file in the source tree. Perhaps we'll eventually end
up with a perl-based configure. We could of course continue on this
road and reinvent the wheel , but I'd rather use some other solution
instead - that would save us some time and the pain of maintainance.

The problems with the combination of autoconf and make are:
- - hard to write (various technologies thrown together). Writing M4
that generates shell scripts that generate perl code that generates
Makefiles is not really the ideal way of working.
- - generates large amount of data (800kb configure script!) that needs
to be in the tarball
- - incompatibilities between various versions of make
- - slow
- - portability layer and build data thrown together
- - duplicated work (other projects need to have the same tests, code)
- - cross-compilation hard to get right (we currently have it, but the
HOSTCC code is rather hackish)

Several alternatives are available - most of which integrate the
configure and build stages. However, we have a large number of
requirements for our build system:

- - distinction between different targets of compilers (build / host)
- - ability to build certain subsystems stand-alone
- - generate pkg-config files for libs
- - it must support custom file types that can be compiled (IDL, asn1,
heimdal et, SWIG, etc)
- - must run on exotic UNIX systems (AIX, IRIX, CrayOS, etc)
- - no external dependencies (e.g. not requiring the installation of
python) in order to build. We consider cc, make and perl valid
requirements for building.
- - optional init function per subsystem that must automatically on
binary startup
- - support for automatic header dependencies (header changes, all files
that use it get recompiled too)

These are pretty heavy requirements. Probably one of the only
applications that I could fine that provides all these requirements is
<a href="http://www.scons.org/">scons</a>. It is small enough to
include in the source tree, but unfortunately depends on python.

We discussed scons earlier and then didn't look at it further because
it was in python, but I'm a bit more convinced we need something like
scons rather then the complicated setup we have now.

One of the ways of solving this could be writing a python script that
generates a configure script and Makefile.in that can then be used on
hosts that do not have python installed. This would be a bit similar
to the 'autogen.sh' script we have currently. I'm not sure how
feasible writing such a script is yet, but I'll be looking at writing
one during the next few days.

Comments ? Thoughts?

Cheers,

Jelmer
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