From: Junio C Hamano <gitster@pobox.com>
Date: Sun, 12 Mar 2017 17:54:16 GMT
Subject: Re: [RFC PATCH] Move SHA-1 implementation selection into a header file
Message-ID: <xmqqfuiiv0s7.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170312130149.czir5hcbosqlmkhb@sigill.intra.peff.net>

Jeff King <peff@peff.net> writes:

> diff --git a/Makefile b/Makefile
> index 9f0eae428..0d65d50e9 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -690,6 +690,7 @@ XDIFF_LIB = xdiff/lib.a
>  VCSSVN_LIB = vcs-svn/lib.a
>  
>  GENERATED_H += common-cmds.h
> +GENERATED_H += hash.h
> ...
> -BASIC_CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER_SQ)' \
> -	$(COMPAT_CFLAGS)
> +BASIC_CFLAGS += $(COMPAT_CFLAGS)
>   ...
> +hash.h:
> +	$(QUIET_GEN)echo '#include $(SHA1_HEADER)' >$@+ && \
> +	{ cmp $@+ $@ >/dev/null 2>/dev/null || mv $@+ $@; }
> +

That looks sensible.  We do not have to adjust the code to update
GIT-BUILD-OPTIONS and friends in this patch because the current way
to force rebuilding when SHA1_HEADER changes is by letting
GIT-CFLAGS file notice the change, and the new "hash.h" itself will
let the $(MAKE) notice if a different hash implementation is chosen
for the build.