This started with the desire to move the setting of the LESS and LV
environment variables into a Makefile knob. But there's a fair bit of
infrastructure involved in that, and this is an attempt to factor out
some of that infrastructure to be more easily reusable. And if we like
the approach, we can move more build-time config in this direction.
There are a couple of things going on here, but the main ideas are:
1. Try to get build-time data into files as much as possible, because
the one thing make understands is dependencies between files. Right
now we rely on sentinel files like GIT-CFLAGS, which have two
downsides:
a. It is easy to miss a dependency that should be in a sentinel
file, leading to failure to rebuild when we should.
b. Because they are so cumbersome to use, we tend to put a lot of
items into a small number of sentinel files, leading to
unnecessary rebuilds (e.g., turning on XDL_FAST_HASH
recompiles _everything_, even though only one C file cares
about it).
2. Some light meta-programming to avoid repeating ourselves and try to
make a few things more readable. I've done this here with $(call)
and $(eval), which are basically the only way to do this in GNU
make (and here we are relying heavily on GNU make, but as far as I
know, nobody has had a huge problem with that in the past).
Frankly, some of it is kind of ugly. And there's some potential for
portability/version problems, just because we're not using more
advanced features. If we don't like that approach, an alternative
is to generate snippets of Makefile in a separate script and
include them (like we do already for GIT-VERSION-FILE). That would
let us write in whatever language we want, and avoid portability
problems. The downside is that it may be less obvious to a reader
not familiar with the system (e.g., you cannot necessarily grep for
all the rules in Makefile, though that is already somewhat the case
with pattern rules).
The two potential criticisms I expect are:
1. Portability issues with $(call), as mentioned above. We avoided
this in 2006, but it may be sufficiently available now. See patch 3
for exact numbers/versions.
2. Some people may simply find it ugly or too confusing for the
benefit. Hence the RFC. :)
While I tried to polish these patches enough to be applied, please take
this mostly as an RFC on the ideas and direction. There are multiple
alternatives to implement some of these things, and I mainly want to see
if people think this sort of make meta-programming is a good idea. The
patches are:
[01/13]: Makefile: drop USE_GETTEXT_SCHEME from GIT-CFLAGS
[02/13]: Makefile: fix git-instaweb dependency on gitweb
These first two are cleanups I noticed in the area, and can be
applied regardless of the rest.
[03/13]: Makefile: introduce make-var helper function
[04/13]: Makefile: use tempfile/mv strategy for GIT-*
[05/13]: Makefile: prefer printf to echo for GIT-*
[06/13]: Makefile: store GIT-* sentinel files in MAKE/
[07/13]: Makefile: always create files via make-var
These ones factor out and improve the GIT-* file handling. Even if
we decide not to go this route, patches 4, 5, and 7 are improvements
that could apply to the current code. I didn't float them to the top
of the series because it would involve making the same change in
several different spots. If we decide not to apply this series, I
can re-roll them as appropriate.
[08/13]: Makefile: introduce sq function for shell-quoting
[09/13]: Makefile: add c-quote helper function
[10/13]: Makefile: drop *_SQ variables
If we accept that we can use $(call), these are further readability
cleanups we can do. They are technically optional, though, with
respect to the rest of the series.
[11/13]: Makefile: auto-build C strings from make variables
[12/13]: Makefile: teach scripts to include make variables
These ones lay the groundwork for easily getting make variables into
shell scripts and C programs.
[13/13]: move LESS/LV pager environment to Makefile
And this one is the point of the series, which is fairly
straightforward because of the earlier groundwork.
-Peff
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