Re: [PATCH v3] new option: object-shortname

Am 03.03.2017 um 10:19 schrieb Mathieu Lirzin:
> Thomas Martitz <[email protected]> writes:
>
>> Maybe I have to explain my use case better? Is it not clear to you?
>
> Yes this is not clear to me. :)
>
> A concrete example will hopefully help.
>
> Thanks.
>


Here we go.

My use case is to make use of non-recursive Automake for faster build 
times and global dependencies, while also generate subdirectory 
Makefiles for the convenience of my co-workers, so that they can keep 
running make only in the directories they work in (they do since since 
15-20 years because our build system always used recursive Automake. I 
can't just remove recursive Automake).

So the setup looks like this:

$ cat root/Makefile.am
include a/Makefile.am.inc
include b/Makefile.am.inc

$ cat root/a/Makefile.am
include Makefile.am.inc

$ cat root/a/Makefile.am.inc
bin_PROGRAMS += %D%/prog_a
%C%_prog_a_SOURCES = a.c
%C%_prog_a_CFLAGS = $(AM_CFLAGS)

$ cat root/b/Makefile.am
include Makefile.am.inc

$ cat root/b/Makefile.am
bin_PROGRAMS += %D%/prog_b
%C%_prog_b_SOURCES = b.c


This generates:
root/Makefile
root/a/Makefile
root/b/Makefile

where root/Makefile does *not* do recursive automake but knows about all 
libs and programs.

This sort of works today, but there is one big problem (assume 
subdir-objects is used)

$ cd root; make a/prog_a
# this compiles prog_a using a/a_prog_a-a.o

$ cd root/a; make prog_a
# this compiles prog_a _again_, using a/prog_a-a.o

As you can see, prog_a is compiled twice simply because the file name of 
the object file is different. This is a big problem.

Now, one workaround would be to use _SHORTNAME

$ echo %C%_prog_a_SHORTNAME = a >> root/a/Makefile.am.inc

This very inconvinient, because it's only need as a workaround and is 
needed in every Makefile.am.inc. But worse, is also unworkable because 
_SHORTNAME does not work inside conditionals.

if ENABLE_PROG_A
include a/Makefile.am.inc
end

generates a Automake warning and generates an incorrect Makefile.in.

We do require Automake conditionals like this because of our modularity.


So my suggested fix is a new Automake option that applies the effect of 
_SHORTNAME automatically without a single line of _SHORTNAME, and 
without the defect when used inside a conditional. As a result, prog_a 
is built from prog_a-a.o regardless of where make was invoked, and is 
not built twice for two make invocations.

The ability to use _SHORTNAME to override even that is, of course, still 
intact.

In the end, if my use case above works, then this would seem to be like 
the ideal way to use Automake to me, since you can combine the best of 
both worlds (recursive and non-recursive Automake).

Best regards