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From: Emily Shaffer <emilyshaffer@google.com>
To: Jonathan Nieder <jrnieder@gmail.com>
Cc: phillip.wood@dunelm.org.uk, "Elijah Newren" <newren@gmail.com>,
	"Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com>,
	"Git Mailing List" <git@vger.kernel.org>,
	"Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
	"Denton Liu" <liu.denton@gmail.com>,
	"Junio C Hamano" <gitster@pobox.com>,
	"Pavel Roskin" <plroskin@gmail.com>,
	"Alban Gruin" <alban.gruin@gmail.com>,
	"SZEDER Gábor" <szeder.dev@gmail.com>
Subject: Re: [PATCH v3 15/15] rebase: change the default backend from "am" to "merge"
Date: Wed, 15 Jan 2020 13:59:22 -0800
Message-ID: <20200115215922.GI181522@google.com> (raw)
In-Reply-To: <20200115195011.GA146834@google.com>

On Wed, Jan 15, 2020 at 07:50:11PM +0000, Jonathan Nieder wrote:
> Hi,
> 
> Phillip Wood wrote:
> > On 11/01/2020 01:16, Elijah Newren wrote:
> 
> >> But the big question here, is what is correct behavior?  Should rebase
> >> call the post-commit hook, or should it skip it?  I haven't any clue
> >> what the answer to that is.
> >
> > It's creating a new commit so I lean towards thinking it should run the
> > post-commit hook. As an example I have a post-commit hook that prints a
> > warning if a commit is created on a branch that is being rewritten by one of
> > my scripts in another worktree. There are pre-commit and pre-rebase hooks to
> > try and prevent that, but the warning is there as a last resort if those
> > hooks are by-passed.
> 
> The initial design for the post-commit hook was
> 
>     commit 89e2c5f17b901edf28a8bb778ece3f6c18bbb721
>     Author: Junio C Hamano <gitster@pobox.com>
>     Date:   Thu Aug 18 17:20:08 2005 -0700
> 
>     Add commit hook and make the verification customizable.
> 
>     There are three hooks:
> 
>         - 'pre-commit' is given an opportunity to inspect what is
>           being committed, before we invoke the EDITOR for the
>           commit message;
> 
>         - 'commit-msg' is invoked on the commit log message after
>           the user prepares it;
> 
>         - 'post-commit' is run after a successful commit is made.
> 
>     The first two can interfere to stop the commit.  The last one is
>     for after-the-fact notification.
> 
> The initial implementation was only in "git commit" and didn't affect
> other commands, but that's an artifact of implementation, not
> intention.  The intention is more murky: certainly "creating a new
> commit" is not the event we want to notify about (for example, "git
> commit-tree" should not invoke the hook), but if I were designing it
> today then all operations that create a new commit and update the
> current branch with it might qualify.
> 
> Even that definition is a bit fuzzy: when I run "git rebase <upstream>
> <branch>", am I updating <branch> or the current branch?  Are
> cherry-picks that carry over changes that were committed previously
> new commits?
> 
> Worse, we have the body of existing post-commit hooks to contend with,
> and each one may have made different assumptions about the semantics.
> We do not have the luxury of designing the hook without regard to that
> body of existing hooks today.

This seems like the most important point to me. I took a very cursory
peek at some search results on Github
(https://github.com/search?l=&q=filename%3A%2Apost-commit%2A&type=Code)
and I see mostly shims - make sure certain files were included in the
commit, bring a worktree up to date, stage stuff that wasn't committed -
but again, that's a very brief glance at over 19000 probable post-commit
hooks. Of course it's not possible for us to examine all of them, but
having these 19k scripts being run lots of times when they didn't used
to during an operation as common as rebase seems a little scary.

> The hook that jiri installs is very simple.  It wants to check when a
> user has (interactively) made a commit on a detached HEAD, to let them
> know that they might want to use "git checkout -b" afterward.  With
> this particular hook, the behavior is better when git rebase does not
> invoke the hook, since in the context of a rebase, the user has no
> need to use "git checkout -b" afterward.  This is a regression, and I
> think we need to take that seriously.
> 
> It doesn't seem like jiri is doing anything weird here, so there's a
> reasonably high probability that other hooks would be affected in the
> same way.  How can we help authors of such hooks to handle this
> change?

This part I do disagree with. Git warns (advice-optional) when I enter
detached HEAD state. When I leave my detached HEAD with some orphaned
commits within (via checkout), I get a warning unconditionally, and an
advice-optional tip to use 'git branch <name> <commit-id>'. The Jiri
hook is warning that these commits I'm making could be lost, but in fact
Git itself is telling me that (and how to save them) at the first moment
when they are actually in danger. So I think this particular example is
not a good one.

I'm more worried about ones like this, although in the rebase case it
may well be a no-op as I can't start a rebase with a dirty index:
https://github.com/alphagov/digitalmarketplace-runner/blob/f8524d9ee7465caef0571d8beb8dff4b25d10fe7/hooks/post-commit

Perhaps a good question is "what could be very catastrophic if it
happened during the middle of a rebase, but not such a bad thing if it
happened when I run 'git commit'?"

> I don't think that starting to invoke the 'post-commit' hook even more
> without going through that thought process is an acceptable fix.
> Since the "right" semantics aren't obvious here, the first step is
> probably to collect some typical examples of post-commit hooks, like
> the example from the message I'm replying to (thank you!).  Ideas for
> where we can find more?

That Github search query I posted above is a pretty big haystack. I
suppose plenty of folks who contribute to Git have a userbase and might
be familiar with some workflows in use there, right?

 - Emily

  reply index

Thread overview: 143+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-20 17:09 [PATCH 00/15] rebase: make the default backend configurable Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 01/15] rebase: extend the options for handling of empty commits Elijah Newren via GitGitGadget
2019-12-20 21:29   ` Junio C Hamano
2019-12-21  0:32     ` Elijah Newren
2019-12-21 18:52       ` Elijah Newren
2019-12-21 23:49       ` Junio C Hamano
2019-12-20 17:09 ` [PATCH 02/15] t3406: simplify an already simple test Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 03/15] rebase, sequencer: remove the broken GIT_QUIET handling Elijah Newren via GitGitGadget
2019-12-20 21:34   ` Junio C Hamano
2019-12-20 17:09 ` [PATCH 04/15] rebase: make sure to pass along the quiet flag to the sequencer Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 05/15] rebase: fix handling of restrict_revision Elijah Newren via GitGitGadget
2019-12-20 21:37   ` Junio C Hamano
2019-12-20 17:09 ` [PATCH 06/15] t3432: make these tests work with either am or merge backends Elijah Newren via GitGitGadget
2019-12-22  5:11   ` Denton Liu
2019-12-23 17:17     ` Elijah Newren
2019-12-20 17:09 ` [PATCH 07/15] rebase: allow more types of rebases to fast-forward Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 08/15] git-rebase.txt: add more details about behavioral differences of backends Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 09/15] rebase: move incompatibility checks between backend options a bit earlier Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 10/15] rebase: add an --am option Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 11/15] contrib: change the prompt for am-based rebases Elijah Newren via GitGitGadget
2019-12-20 23:07   ` SZEDER Gábor
2019-12-21  0:17     ` Elijah Newren
2019-12-20 17:09 ` [PATCH 12/15] rebase tests: mark tests specific to the am-backend with --am Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 13/15] rebase tests: repeat some tests using the merge backend instead of am Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 14/15] rebase: make the backend configurable via config setting Elijah Newren via GitGitGadget
2019-12-20 17:09 ` [PATCH 15/15] rebase: change the default backend from "am" to "merge" Elijah Newren via GitGitGadget
2019-12-20 18:51 ` [PATCH 00/15] rebase: make the default backend configurable Alban Gruin
2019-12-20 18:55   ` Elijah Newren
2019-12-23 18:49 ` [PATCH v2 " Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 01/15] rebase: extend the options for handling of empty commits Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 02/15] t3406: simplify an already simple test Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 03/15] rebase, sequencer: remove the broken GIT_QUIET handling Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 04/15] rebase: make sure to pass along the quiet flag to the sequencer Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 05/15] rebase: fix handling of restrict_revision Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 06/15] t3432: make these tests work with either am or merge backends Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 07/15] rebase: allow more types of rebases to fast-forward Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 08/15] git-rebase.txt: add more details about behavioral differences of backends Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 09/15] rebase: move incompatibility checks between backend options a bit earlier Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 10/15] rebase: add an --am option Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 11/15] contrib: change the prompt for interactive-based rebases Elijah Newren via GitGitGadget
2019-12-23 22:00     ` Denton Liu
2019-12-23 18:49   ` [PATCH v2 12/15] rebase tests: mark tests specific to the am-backend with --am Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 13/15] rebase tests: repeat some tests using the merge backend instead of am Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 14/15] rebase: make the backend configurable via config setting Elijah Newren via GitGitGadget
2019-12-23 18:49   ` [PATCH v2 15/15] rebase: change the default backend from "am" to "merge" Elijah Newren via GitGitGadget
2019-12-24 19:54   ` [PATCH v3 00/15] rebase: make the default backend configurable Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 01/15] rebase: extend the options for handling of empty commits Elijah Newren via GitGitGadget
2020-01-07 14:37       ` Phillip Wood
2020-01-07 19:15         ` Elijah Newren
2020-01-08 14:27           ` Phillip Wood
2020-01-09 21:32             ` Johannes Schindelin
2019-12-24 19:54     ` [PATCH v3 02/15] t3406: simplify an already simple test Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 03/15] rebase, sequencer: remove the broken GIT_QUIET handling Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 04/15] rebase: make sure to pass along the quiet flag to the sequencer Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 05/15] rebase: fix handling of restrict_revision Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 06/15] t3432: make these tests work with either am or merge backends Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 07/15] rebase: allow more types of rebases to fast-forward Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 08/15] git-rebase.txt: add more details about behavioral differences of backends Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 09/15] rebase: move incompatibility checks between backend options a bit earlier Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 10/15] rebase: add an --am option Elijah Newren via GitGitGadget
2020-01-07 14:43       ` Phillip Wood
2020-01-07 19:26         ` Elijah Newren
2020-01-07 20:11           ` Junio C Hamano
2020-01-08 14:32             ` Phillip Wood
2020-01-08 17:18               ` Junio C Hamano
2020-01-08 18:55                 ` Phillip Wood
2019-12-24 19:54     ` [PATCH v3 11/15] git-prompt: change the prompt for interactive-based rebases Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 12/15] rebase tests: mark tests specific to the am-backend with --am Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 13/15] rebase tests: repeat some tests using the merge backend instead of am Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 14/15] rebase: make the backend configurable via config setting Elijah Newren via GitGitGadget
2019-12-24 19:54     ` [PATCH v3 15/15] rebase: change the default backend from "am" to "merge" Elijah Newren via GitGitGadget
2020-01-10 23:14       ` Jonathan Nieder
2020-01-11  1:16         ` Elijah Newren
2020-01-11 14:41           ` Phillip Wood
2020-01-12 17:59             ` Johannes Schindelin
2020-01-16  6:32               ` Elijah Newren
2020-01-16  7:58                 ` Jonathan Nieder
2020-01-16  8:06                   ` Jonathan Nieder
2020-01-16 16:18                     ` Elijah Newren
2020-01-16 20:35                       ` Jonathan Nieder
2020-01-16 21:30                         ` Elijah Newren
2020-01-16 22:39                           ` Jonathan Nieder
2020-01-16 23:19                             ` Elijah Newren
2020-01-16 23:25                           ` Junio C Hamano
2020-01-17  0:51                             ` Elijah Newren
2020-01-16 15:35                   ` Elijah Newren
2020-01-16 20:05                   ` Junio C Hamano
2020-01-16 10:48                 ` Johannes Schindelin
2020-01-12 21:23             ` Junio C Hamano
2020-01-15 19:50             ` Jonathan Nieder
2020-01-15 21:59               ` Emily Shaffer [this message]
2020-01-16  6:14     ` [PATCH v4 00/19] rebase: make the default backend configurable Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 01/19] git-rebase.txt: update description of --allow-empty-message Elijah Newren via GitGitGadget
2020-02-09 15:59         ` Phillip Wood
2020-02-13 18:35           ` Elijah Newren
2020-01-16  6:14       ` [PATCH v4 02/19] t3404: directly test the behavior of interest Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 03/19] rebase (interactive-backend): make --keep-empty the default Elijah Newren via GitGitGadget
2020-02-09 15:59         ` Phillip Wood
2020-02-13 18:52           ` Elijah Newren
2020-01-16  6:14       ` [PATCH v4 04/19] rebase (interactive-backend): fix handling of commits that become empty Elijah Newren via GitGitGadget
2020-02-10 14:27         ` Phillip Wood
2020-02-13 18:54           ` Elijah Newren
2020-02-16 14:46             ` Phillip Wood
2020-01-16  6:14       ` [PATCH v4 05/19] t3406: simplify an already simple test Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 06/19] rebase, sequencer: remove the broken GIT_QUIET handling Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 07/19] rebase: make sure to pass along the quiet flag to the sequencer Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 08/19] rebase: fix handling of restrict_revision Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 09/19] t3432: make these tests work with either am or merge backends Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 10/19] rebase: allow more types of rebases to fast-forward Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 11/19] git-rebase.txt: add more details about behavioral differences of backends Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 12/19] rebase: move incompatibility checks between backend options a bit earlier Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 13/19] rebase: add an --am option Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 14/19] git-prompt: change the prompt for interactive-based rebases Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 15/19] rebase: drop '-i' from the reflog " Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 16/19] rebase tests: mark tests specific to the am-backend with --am Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 17/19] rebase tests: repeat some tests using the merge backend instead of am Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 18/19] rebase: make the backend configurable via config setting Elijah Newren via GitGitGadget
2020-01-16  6:14       ` [PATCH v4 19/19] rebase: change the default backend from "am" to "merge" Elijah Newren via GitGitGadget
2020-01-17 16:58       ` [PATCH v4 00/19] rebase: make the default backend configurable Phillip Wood
2020-02-05 21:06         ` Junio C Hamano
2020-02-05 22:38           ` Elijah Newren
2020-02-15 21:36       ` [PATCH v5 00/20] rebase: make the default backend configurable and change the default Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 01/20] git-rebase.txt: update description of --allow-empty-message Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 02/20] t3404: directly test the behavior of interest Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 03/20] rebase (interactive-backend): make --keep-empty the default Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 04/20] rebase (interactive-backend): fix handling of commits that become empty Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 05/20] t3406: simplify an already simple test Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 06/20] rebase, sequencer: remove the broken GIT_QUIET handling Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 07/20] rebase: make sure to pass along the quiet flag to the sequencer Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 08/20] rebase: fix handling of restrict_revision Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 09/20] t3432: make these tests work with either am or merge backends Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 10/20] rebase: allow more types of rebases to fast-forward Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 11/20] git-rebase.txt: add more details about behavioral differences of backends Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 12/20] rebase: move incompatibility checks between backend options a bit earlier Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 13/20] rebase: add an --am option Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 14/20] git-prompt: change the prompt for interactive-based rebases Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 15/20] rebase: drop '-i' from the reflog " Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 16/20] rebase tests: mark tests specific to the am-backend with --am Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 17/20] rebase tests: repeat some tests using the merge backend instead of am Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 18/20] rebase: make the backend configurable via config setting Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 19/20] rebase: change the default backend from "am" to "merge" Elijah Newren via GitGitGadget
2020-02-15 21:36         ` [PATCH v5 20/20] rebase: rename the two primary rebase backends Elijah Newren via GitGitGadget
2020-02-16 15:01         ` [PATCH v5 00/20] rebase: make the default backend configurable and change the default Phillip Wood

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