[Build-common-hackers] Proposals for multi-build

Jeff Bailey jbailey@nisa.net
Wed, 23 Jul 2003 14:10:16 -0700

I've been thinking about the multi build again.

I think I've reduced it into a series of problems.  The first of which
is that we don't have an adequeate way of using a base variable usually,
and a specific variable only when needed.  This little bit of code
should demonstrate what I mean and provide what I think is an adequeate

all: a b c
cdbs_curpkg = $(filter-out %/,$(subst /,/ ,$@))
cdbs_localval = $(if $($(1)_$(cdbs_curpkg)),"$($(1)_$(cdbs_curpkg))","$($(1))")
foo = foo
foo_b = foo_b
a: c
        @echo a $(call cdbs_localval,foo)
b: a
        @echo b $(call cdbs_localval,foo)
        @echo c $(call cdbs_localval,foo)
.PHONY: a b c all

This produces:

c foo
a foo
b foo_b

My initial proposal is that all of our variable access switch to using
this syntax where it's reasonable that the caller might either user foo
or foo_$(cdbs_curpkg).

The next proposal is much more complicated.

I've approached this with the thought I wanted to see what the
multi-build setup would look like.  I think, based on our earlier
conversations, that I'd like to see this:

Right now we do all of our building in the common hooks.  This is
suboptimal in that we have no per-package flexibility.

I'm assuming here that all builds define DEB_BUILD_MULTI.  If the user
doesn't specify it, then we just fille it with the name of the first
package and proceed.

To handle this, then, a rule from makefile.mk might look like this right

common-build-arch common-build-indep:: common-build-impl

and instead it could look like this:

	$(call cdbs_localval,DEB_MAKE_INVOKE) $(call cdbs_localval,DEB_MAKE_BUILD_TARGET)

I think that doing it this way means that the multi-build stuff will
work without any changes to the buildcore.mk file.  We're *already*
calling these targets.  The only issue then is that we don't run a make
clean between runs, so they need to do VPATH builds.  This is probably
solvable somehow, too, but I haven't thought about it.  

Any comments?  If this looks good, I can dig in on it.

Jeff Bailey

Breathe into my hands, I'll cup them like a glass to drink from...
 - Tattle Tale