Re: [PATCH] Makefile: generate 'git' as 'cc [...] -o git+ && mv git+ git'

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 8, 2021, 17:21 UTC
Message-ID: <xmqqpn097e9o.fsf@gitster.c.googlers.com>
In-Reply-To: <87ft15kegn.fsf@evledraar.gmail.com>

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

Show 7 quoted lines

> We have a lot of existing rules in the Makefile that are of the form:
>
>     make thing >thing+ &&
>     mv thing+ thing
>
> Where we're not doing the rename dance to avoid clobbering the file
> we're reading.

I am afraid that you are totally misreading the intent of that age old convention, which is spelled:

	thing:
		rm -f thing thing+
		prepare contents for thing >thing+
		mv thing+ thing

It protects us from a failure mode where "prepare contents for thing" step is broken and leaves a "thing" that does not work, but confuses make that make does not need to rebuild it, if you wrote it as such:

	thing:
		prepare contents for thing >thing

I think more recent make actually has some knob you can tweak to tell "if the rule failed, remove it", but the convention predates it.

In any case, it is not "we are trying to make thing available while it is being rewritten" at all.