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From: Elijah Newren <newren@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Emily Shaffer" <emilyshaffer@google.com>,
	"Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com>,
	"Git Mailing List" <git@vger.kernel.org>,
	"Jeff King" <peff@peff.net>,
	"Johannes Schindelin" <Johannes.Schindelin@gmx.de>,
	"Phillip Wood" <phillip.wood@dunelm.org.uk>,
	"Denton Liu" <liu.denton@gmail.com>,
	"Pavel Roskin" <plroskin@gmail.com>,
	"Alban Gruin" <alban.gruin@gmail.com>,
	"SZEDER Gábor" <szeder.dev@gmail.com>,
	"Jonathan Nieder" <jrnieder@gmail.com>
Subject: Re: [PATCH v5 20/20] rebase: rename the two primary rebase backends
Date: Thu, 12 Mar 2020 12:29:45 -0700
Message-ID: <CABPp-BGvqUEDoj6_mUAsSVeS8+h5ruCFcMTENtf5LY2XWKVj-g@mail.gmail.com> (raw)
In-Reply-To: <xmqqftedfkvy.fsf@gitster.c.googlers.com>

On Thu, Mar 12, 2020 at 12:12 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Elijah Newren <newren@gmail.com> writes:
>
> > On Thu, Mar 12, 2020 at 8:13 AM Emily Shaffer <emilyshaffer@google.com> wrote:
> >> ...
> >> This broke quite a few upstream users for us today...
>
> One more thing I've been wondering was if we should really have said
> "ok, the two known gotchas have been dealt with, so let's ship it".
> It is quite likely that users may be hit by remaining differences
> between the merge and apply backends that we assume to be merely
> subtle and easy-to-work-around ones, and it may be prudent to use
> the "let's not change the default just yet, but ask people to test
> it in their workflow by advertising the configuration" patch.

Good question, but there's several things to unpack here...

First, note that this particular breakage would have occurred
regardless of the default setting, because the problem was that they
setting rebase.backend to an unrecognized value, not that we used a
different backend than they were used to.

Second, for the particular case of the post-commit hook that they
referenced in their rationale, that item was documented near the end
of the 2.25 cycle and mentioned in previous patchsets[1, 2] so I
figured this case was already considered.

Those two points may obscure the issue, though; your question is still
valid.  I think the bigger question is whether there are other unknown
differences, or even known differences that are a bigger issue than we
currently realize.  That's hard to judge, and it may not be possible
to judge until we've flipped the default.  As such, it's a judgement
call.  I can see the judgement call going either way.  A couple things
to weigh in on how to go:
   - Making rebase.backend default to 'apply' for 2.26 is certainly
the conservative option and may give us more feedback and time to iron
out differences
   - We had multiple complaints this cycle about rebase.backend=apply
merging things incorrectly with the only workaround being to use the
merge backend[3,4]
   - The rebase-backend topic wasn't merged down to master until less
than a week before -rc0.  (For a variety of reasons.)  A big change
like this probably would have been better to merge down earlier in
some cycle.

To be honest, if I was maintainer, I'm not sure which direction I'd
pick.  If you feel safer switching the default backend to apply for
this cycle and then (re-)revert it early next cycle to the merge
backend, I think that's totally reasonable.


[1] https://lore.kernel.org/git/pull.679.v4.git.git.1579155273.gitgitgadget@gmail.com/
[2] https://lore.kernel.org/git/CABPp-BHONuRyt8VJqRuoCF2rGYZ5EhH9KJXQZ3NO69rYwA5J3g@mail.gmail.com/
[3] https://lore.kernel.org/git/CABPp-BGiu2nVMQY_t-rnFR5GQUz_ipyEE8oDocKeO+h+t4Mn4A@mail.gmail.com/
[4] https://lore.kernel.org/git/20200108223557.GE32750@szeder.dev/

  reply index

Thread overview: 161+ 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
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
2020-03-12 15:13           ` Emily Shaffer
2020-03-12 16:33             ` Elijah Newren
2020-03-12 17:55               ` Jonathan Nieder
2020-03-12 18:39                 ` Elijah Newren
2020-03-12 18:46                   ` Jonathan Nieder
2020-03-12 19:31                     ` Elijah Newren
2020-03-17  2:58                       ` Jonathan Nieder
2020-03-17  4:45                         ` Elijah Newren
2020-03-12 19:54                     ` Junio C Hamano
2020-03-12 19:07               ` Junio C Hamano
2020-03-12 19:12                 ` Jonathan Nieder
2020-03-12 19:12               ` Junio C Hamano
2020-03-12 19:29                 ` Elijah Newren [this message]
2020-03-12 20:37                   ` Jeff King
2020-03-12 21:27                     ` Junio C Hamano
2020-03-12 22:06                       ` Elijah Newren
2020-03-13  0:04                         ` Junio C Hamano
2020-03-12 23:30                       ` Jonathan Nieder
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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