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From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	git@vger.kernel.org, "Andreas Färber" <andreas.faerber@web.de>,
	"Johannes Schindelin" <Johannes.Schindelin@gmx.de>
Subject: Re: [PATCH 3/6] Makefile: refactor out "ln || ln -s || cp" pattern
Date: Tue, 30 Mar 2021 11:20:02 -0400	[thread overview]
Message-ID: <YGNBoljqknW+Kpif@coredump.intra.peff.net> (raw)
In-Reply-To: <xmqqsg4dha3i.fsf@gitster.g>

On Mon, Mar 29, 2021 at 03:24:33PM -0700, Junio C Hamano wrote:

> Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:
> 
> > Refactor out the hard-to-read and maintain "ln || ln -s || cp"
> > pattern.
> >
> > This was initially added in 3e073dc5611 (Makefile: always provide a
> > fallback when hardlinks fail, 2008-08-25), but since then it's become
> > a lot more complex as we've added:
> >
> >  * 3426e34fedd (Add NO_CROSS_DIRECTORY_HARDLINKS support to the
> >    Makefile, 2009-05-11)
> >
> >  * NO_INSTALL_HARDLINKS in 70de5e65e8c (Makefile:
> >    NO_INSTALL_HARDLINKS, 2012-05-02)
> >
> >  * INSTALL_SYMLINKS in ad874608d8c (Makefile: optionally symlink
> >    libexec/git-core binaries to bin/git, 2018-03-13)
> >
> >  * SKIP_DASHED_BUILT_INS 179227d6e21 (Optionally skip linking/copying
> >    the built-ins, 2020-09-21)
> >
> > Each of those commits had to add a new special-case to this code,
> > resulting in quite an unmaintainable mess for adding any sort of new
> > option.
> >
> > Let's use the newly introduced ln-or-cp.sh script instead, note that
> > we only sometimes pass the --no-cross-directory-hardlinks option, per
> > the previous behavior. The target of the "ln -s" is also another
> > special snowflake, but we're careful to carry that forward.
> 
> Nice.  These explicit command-line options to the helper may be
> harder to initially write and maintain than just exporting the
> relevant $(MAKE) macros and using it from the helper, but once
> it works correctly, it is much easier to see what is going on.

Another option is to make "ln-or-cp" itself a target that "make" knows
how to build, and bake the values into its "built" version. Besides
making the invocations a bit shorter, it also means that the dependency
graph is more correct. If a rule invokes ln-or-cp, its behavior will
change if $NO_INSTALL_HARDLINKS changes, for example. Telling that to
make requires depending on a sentinel file in each such caller (like
GIT-BUILD-OPTIONS). Whereas we could do that once for the "ln-or-cp"
target, and then everyone who uses it just depends on it.

I had a series a long time ago that moved the whole Makefile in that
direction, but I got nervous that it was too disruptive and too
non-idiomatic to be worth pursuing. So I offer the alternative here
mostly as food for thought. It may not be a good direction (and we
already have good-enough solutions, like depending on
GIT-BUILD-OPTIONS).

-Peff

  reply	other threads:[~2021-03-30 15:21 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-07 13:20 [PATCH] Makefile: generate 'git' as 'cc [...] -o git+ && mv git+ git' Ævar Arnfjörð Bjarmason
2021-03-07 20:41 ` Junio C Hamano
2021-03-08 12:38   ` Ævar Arnfjörð Bjarmason
2021-03-08 17:21     ` Junio C Hamano
2021-03-08 18:26     ` Jeff King
2021-03-29 16:20 ` [PATCH v2 0/5] Makefile: don't die on AIX with open ./git Ævar Arnfjörð Bjarmason
2021-03-29 16:20   ` [PATCH v2 1/5] Makefile: rename objects in-place, don't clobber Ævar Arnfjörð Bjarmason
2021-03-29 18:21     ` Junio C Hamano
2021-03-29 18:26       ` Junio C Hamano
2021-03-29 23:24       ` Ævar Arnfjörð Bjarmason
2021-03-30  0:21         ` Junio C Hamano
2021-03-31 14:17           ` Ævar Arnfjörð Bjarmason
2021-03-31 18:50             ` Junio C Hamano
2021-03-29 16:20   ` [PATCH v2 2/5] Makefile: rename scripts " Ævar Arnfjörð Bjarmason
2021-03-29 18:40     ` Junio C Hamano
2021-03-29 23:28       ` Ævar Arnfjörð Bjarmason
2021-03-29 16:20   ` [PATCH v2 3/5] Makefile: don't needlessly "rm $@ $@+" before "mv $@+ $@" Ævar Arnfjörð Bjarmason
2021-03-29 18:46     ` Junio C Hamano
2021-03-29 16:20   ` [PATCH v2 4/5] Makefile: add the ".DELETE_ON_ERROR" flag Ævar Arnfjörð Bjarmason
2021-03-29 18:51     ` Junio C Hamano
2021-03-29 23:31       ` Ævar Arnfjörð Bjarmason
2021-03-29 23:58         ` Junio C Hamano
2021-03-30 15:11         ` Jeff King
2021-03-30 18:36           ` Junio C Hamano
2021-03-31  6:58             ` Jeff King
2021-03-31 18:36               ` Junio C Hamano
2021-03-31 22:29                 ` Johannes Schindelin
2021-03-29 16:20   ` [PATCH v2 5/5] Makefile: don't "rm configure" before generating it Ævar Arnfjörð Bjarmason
2021-03-29 16:31   ` [PATCH 0/6] Makefile: make non-symlink & non-hardlink install sane Ævar Arnfjörð Bjarmason
2021-03-29 16:31     ` [PATCH 1/6] Makefile: symlink the same way under "symlinks" and "no hardlinks" Ævar Arnfjörð Bjarmason
2021-03-29 22:17       ` Junio C Hamano
2021-03-29 16:31     ` [PATCH 2/6] Makefile: begin refactoring out "ln || ln -s || cp" pattern Ævar Arnfjörð Bjarmason
2021-03-29 22:20       ` Junio C Hamano
2021-03-29 16:31     ` [PATCH 3/6] Makefile: refactor " Ævar Arnfjörð Bjarmason
2021-03-29 22:24       ` Junio C Hamano
2021-03-30 15:20         ` Jeff King [this message]
2021-03-30 18:36           ` Junio C Hamano
2021-03-29 16:31     ` [PATCH 4/6] Makefile: make INSTALL_SYMLINKS affect the build directory Ævar Arnfjörð Bjarmason
2021-03-29 22:31       ` Junio C Hamano
2021-03-31 14:04         ` Ævar Arnfjörð Bjarmason
2021-03-29 16:31     ` [PATCH 5/6] Makefile: use "ln -f" instead of "rm && ln" Ævar Arnfjörð Bjarmason
2021-03-29 22:46       ` Junio C Hamano
2021-03-29 16:31     ` [PATCH 6/6] Makefile: add a INSTALL_FALLBACK_LN_CP mode Ævar Arnfjörð Bjarmason
2021-03-29 22:53       ` Junio C Hamano
2021-03-31 14:03         ` Ævar Arnfjörð Bjarmason
2021-03-31 18:45           ` Junio C Hamano
2021-03-31 19:01             ` Ævar Arnfjörð Bjarmason
2021-03-29 23:08     ` [PATCH 0/6] Makefile: make non-symlink & non-hardlink install sane Junio C Hamano

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