[Build-common-hackers] Bug#202385: Configuration variable to load modules instead of using include

[Chris Halls]

Package: cdbs
Version: 0.4.4
Severity: wishlist

First of all, cdbs is really cool, thanks for making it :)

I have a suggestion for the way classes/modules are included.  Instead
of including the modules for every file, define a variable similar to
DEB_BUILD_OPTIONS that contains the list of modules to load, and then
use a single include line:

  include /usr/share/cdbs/1/rules/debhelper.mk
  include /usr/share/cdbs/1/class/autotools.mk
  include /usr/share/cdbs/1/rules/simple-patchsys.mk

becomes for example:

  CDBS_MODULES=debhelper,autotools,simple-patchsys
  include /usr/share/cdbs/1/rules/buildcore.mk

And in buildcore, or even another file if you prefer, you create stanzas
such as:

  ifneq (,$(findstring debhelper,$(CDBS_MODULES)))
    include $(_cdbs_rules_path)/debhelper.mk
  endif

  ifneq (,$(findstring autotools,$(CDBS_MODULES)))
    include $(_cdbs_class_path)/autotools.mk
  endif

  ifneq (,$(findstring debhelper,$(CDBS_MODULES)))
    include $(_cdbs_rules_path)/simple-patchsys.mk
  endif

This should make it easier to write rules files (if cdbs didn't make it
easy enough already :), and I think will prevent some potential
problems:

 * Because you get to decide in which order the files are included, you
   prevent users from forgetting to do this:
     Incidentally, you should usually include debhelper.mk first, before
     other rules.  This will turn on optional Debhelper-using parts of
     other rules, if any, which is usually what you want. (README.gz)

   So future changes of such requirements can be implemented more
   transparently to the users, because the complete list of modules is
   available from the start. 

 * The version-specific subdirectory is only declared once in the user
   rules file, so you can't get inconsistencies like this:

  include /usr/share/cdbs/1/rules/debhelper.mk
  include /usr/share/cdbs/2/class/autotools.mk

Chris