Re: [PATCH] commit: Add -f, --fixes <commit> option to add Fixes: line

From: Junio C Hamano
Date: Mon Oct 28 2013 - 05:08:58 EST

Junio C Hamano <gitster@xxxxxxxxx> writes:

> There are unbound number of kinds of trailers people would want to
> add, depending on their projects' needs. We should not have to add
> a specific support for a tailer like this one, before thinking
> through to see if we can add generic support for adding arbitrary
> trailers to avoid code and interface bloat.
> Think of the existing --signoff as a historical mistake. Such a
> generic "adding arbitrary trailers" support, when done properly,
> should be able to express what "--signoff" does, and we should be
> able to redo "--signoff" as a special case of that generic "adding
> arbitrary trailers" support, and at that point, "Fixes:" trailer the
> kernel project wants to use should fall out as a natural consequence.

Thinking aloud further, what I had in mind was along the lines of
the following.

* The most generic external interface would be spelled as

--trailer <token>[=<param>]

where <token> can be things like "signoff", "closes", "acked-by",
"change-id", "fixes", etc.; they can be taken from an unbounded
set. The historical "--signoff" can become a short-hand for
"--trailer signoff". More than one "--trailer" option can be
given on a single command line.

* The token is used to look into the configuration, e.g.,

[commitTrailer "signoff"]
style = append-norepeat
trailer = Signed-off-by

[commitTrailer "change-id"]
style = append-only-if-missing
trailer = Change-Id
command = 'git hash-object -t commit --stdin <$GIT_PROTO_COMMIT'

[commitTrailer "fixes"]
style = overwrite
trailer = Fixes
command = 'git log -1 --oneline --format="%h (%s)" --abbrev-commit=14 $ARG'


- "commitTrailer.<token>.style" defines the interaction with
existing trailer of the same kind (e.g. S-o-b: accumulates by
appending, but we try not to repeat the same sign-off twice
which would show you forwarding your own message you are the
last person in the Sign-off chain; Fixes: if there is already
one will remove the old one and replaces; etc.);

- "commitTrailer.<token>.trailer" defines the trailer label at
the beginning of the trailer line;

- "commitTrailer.<token>.command" gives the command to run to
obtain the payload after the "trailer" label. A handful
obvious and useful variables are exported for the command to
use, and <param> is exported as $ARG, if present.

With the most generic syntax, with the above commitTrailer.fixes.*
configuration, I would imagine that you can say something like:

git commit --trailer fixes="v2.6.12^{/^i386: tweak frobnitz}"

to say that the first commit you find traversing the history of
v2.6.12 whose title is "i386: tweak frobnitz" was faulty, and you
are creating a commit that corrects its mistake.

Giving some default configuration to often used trailer types
(e.g. configuration for "--trailer signoff") and promoting some
commonly used ones into a separate built-in option (e.g. an option
"--signoff" that does not have to say "--trailer signoff") are
entirely separate issues, and only time can nudge us into evaluating
individual types of trailers.
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