On Fri, May 11, 2007 at 10:10:26AM -0700, Junio C Hamano wrote:
> I have not been very sympathetic to config.mak from the
> beginning, although people seem to want it. As I try to arrange
> variable overrides to be passed from the command line anyway,
> I've not used config.mak myself.
>
> [...]
>
> (3) The volunteer cooks up an improved Makefile, using
> config.mak "non-stock" testers have.
I wonder if we would be better served by moving these sorts of
build-time configuration decisions into the actual make dependency
tree. E.g., something like:
openssl.lib: mklib-openssl.sh conf-openssl
sh mklib-openssl.sh <conf-ssl >openssl.lib
program: main.o openssl.lib:
cc -o "$@" main.o `cat openssl.lib`
where conf-openssl specifies the user's preference (either actual
library paths, "auto" for autodetection, or "none" not to use it at
all), and mklib-openssl is a script that converts that into the command
line options for the link.
You can of course do the same with creating a .h file to choose an
implementation (you just make a file that #define's the correct thing).
The nice thing about this approach is that:
1. You move configuration cruft out of the Makefile, making it much
easier to read. Instead, you have a series of very small and
obvious shell scripts.
2. The dependency chain is actually correct. If I edit conf-openssl,
then that should trigger a re-link for everything which compiles
against it.
You can also use this for portability fixes:
program: main.o strcasestr.o
cc -o "$@" main.o strcasestr.o
strcasestr.o choose try_strcasestr.c compat/strcasestr.c
sh choose try_strcasestr.c compat/strcasestr.c
where choose is a script that compiles and runs some test program and
uses the result to choose a source file to become strcasestr.c. Thus you
_always_ link against strcasestr.o, it's just that sometimes there's an
implementation of strcasestr in it (if required by the platform) and
sometimes it's empty (or an alternate implementation, etc).
I have used this technique many times, and would be happy to be involved
in changing the Makefile. However, it's going to be quite a large
change, and I recognize that this style is not familiar to most people,
so obviously that should be taken into account.
-Peff
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