Re: [PATCH 3/3] commit: add an option the reword HEAD

[Phillip Wood <phillip.wood123@gmail.com>]

Hi Dscho

On 23/09/2020 21:42, Johannes Schindelin wrote:
> Hi Phillip,
> 
> On Wed, 23 Sep 2020, Phillip Wood wrote:
> 
>> On 23/09/2020 11:22, Johannes Schindelin wrote:
>>>
>>> On Mon, 21 Sep 2020, Phillip Wood via GitGitGadget wrote:
>>>
>>>> From: Phillip Wood <phillip.wood@dunelm.org.uk>
>>>>
>>>> If one notices a typo in the last commit after starting to stage
>>>> changes for the next commit it is useful to be able to reword the last
>>>> commit without changing its contents. Currently the way to do that is
>>>> by specifying --amend --only with no pathspec which is not that
>>>> obvious to new users (so much so that before beb635ca9c ("commit:
>>>> remove 'Clever' message for --only --amend", 2016-12-09) commit
>>>> printed a message to congratulate the user on figuring out how to do
>>>> it). If the last commit is empty one has to pass --allow-empty as well
>>>> even though the contents are not being changed. This commits adds a
>>>> --reword option for commit that rewords the last commit without
>>>> changing its contents.
>>>
>>> I would like to explain the idea I tried to get across when I proposed to
>>> implement support for `reword!` (and `--reword`) because I feel that it
>>> will change the design of this patch in a rather big way.
>>>
>>> First of all, let me explain the scenario in which I long for the
>>> `--reword` option: I maintain several patch thickets, the most obvious one
>>> being Git for Windows' patch thicket that is merge-rebased [*1*] onto
>>> every new Git version.
>>>
>>> At times, I need to adjust a commit message in that patch thicket. It
>>> would be quite wasteful to perform a full merge-rebase, therefore I
>>> typically call `git commit --squash <commit> -c <commit>`, copy the
>>> oneline, paste it after the `squash!` line (surrounded by empty lines), and
>>> then reword the commit message. When the next Git version comes out, I do
>>> a merging-rebase, and when the editor pops up because of that `squash!`
>>> oneline, I remove the now-obsolete version(s) of the commit message.
>>>
>>> Obviously, I have to be careful to either also pass `--only` (which I
>>> somehow managed to learn about only today) or I have to make sure that I
>>> have no staged changes. In practice, I actually specify a bogus path,
>>> which has the same effect as `--only`.
>>>
>>> What I would actually rather have is the `--reword` option: `git commit
>>> --reword <commit>`. In my mind, this would _add_ a new, "empty" commit,
>>> letting me edit the commit message of the specified commit, and using that
>>> as commit message, prefixed with the line `reword! <oneline>`.
>>>
>>> This, in turn, would need to be accompanied by support in the interactive
>>> rebase, to perform the desired reword (which is admittedly quite a bit
>>> different from what the way the todo command `reword` works).
>>>
>>> With that in mind, I would like to caution against the design of your
>>> current patch, because it would slam the door shut on the way I would like
>>> `--reword` to work.
>>
>> I'm keen to have an easy way to reword HEAD and a way to implement your
>> reword! idea.
>>
>> I posted a comment on your gitgitgadget issue about reword! and drop![1]
>> pointing to some patches[2] that implement the reword! idea as amend!. I think
>> we want to be able to  fixup a commit and reword it at the same time which is
>> way I chose the name amend! rather than reword! The implementation currently
>> changes `git commit --amend` to take an optional commit which isn't ideal. I
>> wonder if calling it revise! would be better then we could have `git commit
>> --reword` to reword HEAD and `git commit --revise <commit>` to create a commit
>> that will reword and fixup <commit> when the user runs `git rebase -i
>> --autostash`. fold! is another possibility.
>>
>> I don't think this patch series stops us implementing something for rebase but
>> it would mean we couldn't use the name reword! unless we allow `git commit
>> --reword` to take an optional commit which I'm not that keen on.
>>
>> What do you think to an alternative name?
> 
> I am really worried that the proliferation of confusingly similar options
> will increase Git's reputation for being awfully hard to use.

That is certainly a consideration, but not having a way to easily reword 
the last commit without changing its contents does not to improve Git's 
user friendliness. If you only just discovered using --only for 
rewording it's a fair bet a lot of regular users are unaware of it.

The reason I'm not keen on having --amend or --reword take an optional 
commit is that I think it is confusing as it means sometimes that option 
creates a new commit and sometimes it modifies the last commit 
furthermore passing --reword=HEAD would not reword HEAD but creates a 
reword! commit.

Rewording the last commit and creating a reword! commit are two 
different operations so I'm not sure having different options for them 
is that bad. To me the real confusion is that we end up with 3 options 
that create different flavors of fixup commits. It would be much nicer 
if there was a single fixup type that reworded the message as well as 
fixing up the contents and users just passed `--no-edit` to avoid 
changing the message. I'd really like to somehow change the semantics of 
`git commit --fixup/--squash` and the rebase `fixup`/`squash` commands 
to actually reword the commit. I guess that would mean an opt-in config 
setting which isn't ideal.

As an aside I'd like to see a new `rewrite` command that wraps the 
functionality of `rebase -i` so the user does not have to deal with 
fixups and editing a todo list. `git rewrite amend <commit>` would be 
equivalent to starting a rebase and marking <commit> as `edit`, the user 
can then make their changes and run `git rewrite continue` which would 
finish the rebase or `git rewrite amend <another-commit>` which would 
either alter the todo list to mark <another-commit> as `edit` or create 
new entries to rewind the rebase if <another-commit> is not in the todo 
list and then run `git rebase --continue`. Additionally there would be 
`reword` and `drop` commands and support for blame so that the user can 
do all this from an editor which would run `git rewrite amend -L 
<current-line> <current-file>` to amend the commit that introduced the 
current line. I've got a nasty scheme prototype of this and I've found 
it really useful. For an individual developer developing a patch series 
it is much more convenient to just edit the history directly rather than 
creating fixup! commits (which often seem to have conflicts when they 
are applied). It would not address your use where you don't want to be 
rebasing all the time though.

Best Wishes

Phillip

> Ciao,
> Dscho
>