Automatic dependency tracking in the Git build system (was: Re: [PATCHv2 1/8] Makefile: apply dependencies consistently to sparse/asm targets)

[Adding the Automake list in CC:]

On 06/20/2012 09:57 PM, Jeff King wrote:

On Wed, Jun 20, 2012 at 02:45:31PM -0500, Jonathan Nieder wrote:

quoted

Jeff King wrote:

quoted

Did you read the argument in patch 2? They are almost certainly not
helping anyone, anyway.

Yes, I read patch 2. I hacked on git from time to time in the days
before COMPUTE_HEADER_DEPENDENCIES, and it sometimes involved changing
header files. When they were not in LIB_H, the experience was much
nicer.

Is that called "not helping"? I'm afraid I don't follow this line of
argument at all.

I just assumed that people who are actively hacking on individual header
files in git actually have a compiler that can do COMPUTE_HEADER_DEPENDENCIES.
Maybe that is not the case. If it were such a big deal, then why is
everything in LIB_H? Why don't people use these manual rules, or convert
existing LIB_H entries to use them?

For people who are not actively hacking on header files in git, the
arguments from that patch apply (namely that LIB_H is so gigantic that
you are unlikely to hit a specific change where one of the few manual
rules is triggered, but LIB_H is not).

quoted

On the other hand, if someone were proposing adding a simple awk
script to implement a "make dep" fallback, I would understand that.

I'd be OK with that. Do you have one in mind, or do we need to write it
from scratch? Surely somebody else has solved this problem before.

[begin shameless plug]

Have you taken a look at the 'depcomp' script that comes with Automake?
 <http://git.savannah.gnu.org/cgit/automake.git/tree/lib/depcomp>
Once you get past some of its idiosyncrasies and few historical warts,
it has a lot of built-in knowledge about automatic dependency tracking
for a lot of different compilers.

[end shameless plug]

HTH,
  Stefano