Michael J Gruber <g...@drmicha.warpmail.net> writes:

> Junio C Hamano venit, vidit, dixit 06.09.2012 07:07:
>> Michael J Gruber <g...@drmicha.warpmail.net> writes:
>>> The pre-commit hook is often used to ensure certain properties of each
>>> comitted tree like formatting or coding standards, validity (lint/make)
>>> or code quality (make test). But merges introduce new commits unless
>>> they are fast forwards, and therefore they can break these properties
>>> because the pre-commit hook is not run by "git merge".
>>> Introduce a pre-merge hook which works for (non ff, automatic) merges
>>> like pre-commit does for commits. Typically this will just call the
>>> pre-commit hook (like in the sample hook), but it does not need to.
>> When your merge asks for a help from you to resolve conflict, you
>> conclude with "git commit", and at that point, pre-commit hook will
>> have a chance to reject it, presumably.  That means for any project
>> that wants to audit a merge via hook, their pre-commit hook MUST be
>> prepared to look at and judge a merge.  Given that, is a separate
>> hook that "can just call the pre-commit but does not need to" really
>> needed and useful?
>> I admit that I haven't thought things through, but adding a boolean
>> "merge.usePreCommitHook" smells like a more appropriate approach to
>> me.
>> I dunno.
> That would be an option ;)

I said "I dunno" as others may have opinions on the best direction
to go.

> Either works for me, and if we don't change the current behaviour
> (pre-commit-hook resp. no hook for non-automatic merges resp. automatic
> merges) the config option is probably less confusing.

If we were to go in the "pre-commit has to be prepared to vet a
merge already, so let it handle the automerge case" direction, I
have another suggestion.

Because you need to support "merge --no-verify" to override the hook
anyway, I think it makes sense to introduce "merge --verify" to
force it trigger the hook (and it needs to percolate up to "pull").

People who want it always on may want a boolean merge.verify, but
that should come in a separate step.  The patch that implements it
must make sure all our internal uses of "merge" is updated to pass
"--no-verify", unless there is a very good reason.

Another direction to go would be to deprecate the "commit is the way
to conclude a merge that stopped in the middle due to a conflict
asking for your help" and introduce "merge --continue" [*1*].  That
would open a way to a separate "pre/post-merge" hook much cleanly.
At that point it would be clear that "pre-commit" won't be involved
in "merge" (i.e. the user never will use "git commit" when merging).

I am fairly negative on the current mess imposed on "git commit"
that has to know who called it and behave differently (look for
"whence" in builtin/commit.c), and would rather not to see it made
worse by piling "call pre-merge if exists and in a merge, or call
pre-commit" kind of hack on top of it.


*1* This has been brought up a few times during discussion on
sequencer and mergy operations, and I think it makes sense in the
longer term.  "am" and "rebase" were first to use "--continue",
instead of having the user to use "commit" to conclude, and later
"cherry-pick" and "revert" have been updated to follow suit, so
"merge" may be the only oddball remaining now.
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