[Bug] commit cleanup does not happen during autosquash rebase

> 
> What did you do before the bug happened? (Steps to reproduce your issue)
> 
> 1. Initialize a git repo with `git init`
> 2. Install a custom `prepare-commit-msg` hook that injects some comments
>    - Intention: inject the output of `git log --oneline -n10` during
> interactive commit, so I can see past commits
> 3. Run `git config commit.cleanup strip`
>    - Intention: strip the injected comments too in non-interactive mode
> (e.g. `git cherry-pick` & `git rebase`)
> 4. Run `touch foo && git add -A && git commit -m "Initial commit"`
> 5. Run `touch bar && git add -A && git commit --fixup=@`
> 6. Run `git rebase --root --autosquash`

> What did you expect to happen? (Expected behavior)
> 
> Git would perform the autosquash, while keeping the commit message of
> the squash target unchanged.
> 
> What happened instead? (Actual behavior)
> 
> Git performed the autosquash, but the commit message of the squash
> target is now clobbered with my injected comments.

> What's different between what you expected and what actually happened?
> 
> I expected commit cleanup to happen during the autosquash. It seems
> like that didn't happen.
> 
> Anything else you want to add:
> 
> Here is my `prepare-commit-msg` script. But I expect this issue to be
> replicable with anything that injects comments.
> 
> ```
> #!/usr/bin/env bash
> {
>    echo '# Last 10 commits:'
>    git log --oneline -n 10 --decorate=short | sed 's/^/#   /'
>    echo '#'
> } >> "$1"
> ```
> 
> Please review the rest of the bug report below.
> You can delete any lines you don't wish to share.
> 
> 
> [System Info]
> git version:
> git version 2.50.1
> cpu: x86_64
> built from commit: d82adb61ba2fd11d8f2587fca1b6bd7925ce4044
> sizeof-long: 8
> sizeof-size_t: 8
> shell-path: /bin/sh
> libcurl: 8.14.1
> OpenSSL: OpenSSL 3.5.1 1 Jul 2025
> zlib-ng: 2.2.4
> SHA-1: SHA1_DC
> SHA-256: SHA256_BLK
> uname: Linux 6.12.41-1-lts #1 SMP PREEMPT_DYNAMIC Fri, 01 Aug 2025
> 20:42:03 +0000 x86_64
> compiler info: gnuc: 15.1
> libc info: glibc: 2.42
> $SHELL (typically, interactive shell): /bin/bash
> 
> 
> [Enabled Hooks]
> prepare-commit-msg
> 

>
> Hi Simon
>
> On 13/08/2025 12:39, Simon Cheng wrote:
> >
> > What did you do before the bug happened? (Steps to reproduce your issue)
> >
> > 1. Initialize a git repo with `git init`
> > 2. Install a custom `prepare-commit-msg` hook that injects some comments
> >    - Intention: inject the output of `git log --oneline -n10` during
> > interactive commit, so I can see past commits
> > 3. Run `git config commit.cleanup strip`
> >    - Intention: strip the injected comments too in non-interactive mode
> > (e.g. `git cherry-pick` & `git rebase`)
> > 4. Run `touch foo && git add -A && git commit -m "Initial commit"`
> > 5. Run `touch bar && git add -A && git commit --fixup=@`
> > 6. Run `git rebase --root --autosquash`
>
> Thanks for providing a simple way to reproduce this
>
> > What did you expect to happen? (Expected behavior)
> >
> > Git would perform the autosquash, while keeping the commit message of
> > the squash target unchanged.
> >
> > What happened instead? (Actual behavior)
> >
> > Git performed the autosquash, but the commit message of the squash
> > target is now clobbered with my injected comments.
>
> It looks like this stems from f7d42ceec52 (rebase -i: do leave commit
> message intact in fixup! chains, 2021-01-28) which was added in response
> to a bug report[1]. That commit switched from always cleaning up the
> fixup message to never cleaning it up. I wonder if instead we should be
> respecting the user's commit.cleanup setting. The commit message says
> that should not respect commit.cleanup because we want to use the
> message verbatim but that is not what we do with "pick" commands which
> respect commit.cleanup if it is set. Given that we call the
> prepare-commit-msg hook we cannot be sure that we're reusing the
> original commit message verbatim anyway so I think we should probably
> change "fixup" commands to use the same cleanup flags as "pick" commands.
>
> I'm going to be off the list for a week from tomorrow but I'll try and
> look at this again when I'm back if no one else has picked it up in the
> meantime.
>
> Thanks
>
> Phillip
>
> [1]
> https://lore.kernel.org/git/CANVGpwZGbzYLMeMze64e_OU9p3bjyEgzC5thmNBr6LttBt+YGw@mail.gmail.com/
>
> > What's different between what you expected and what actually happened?
> >
> > I expected commit cleanup to happen during the autosquash. It seems
> > like that didn't happen.
> >
> > Anything else you want to add:
> >
> > Here is my `prepare-commit-msg` script. But I expect this issue to be
> > replicable with anything that injects comments.
> >
> > ```
> > #!/usr/bin/env bash
> > {
> >    echo '# Last 10 commits:'
> >    git log --oneline -n 10 --decorate=short | sed 's/^/#   /'
> >    echo '#'
> > } >> "$1"
> > ```
> >
> > Please review the rest of the bug report below.
> > You can delete any lines you don't wish to share.
> >
> >
> > [System Info]
> > git version:
> > git version 2.50.1
> > cpu: x86_64
> > built from commit: d82adb61ba2fd11d8f2587fca1b6bd7925ce4044
> > sizeof-long: 8
> > sizeof-size_t: 8
> > shell-path: /bin/sh
> > libcurl: 8.14.1
> > OpenSSL: OpenSSL 3.5.1 1 Jul 2025
> > zlib-ng: 2.2.4
> > SHA-1: SHA1_DC
> > SHA-256: SHA256_BLK
> > uname: Linux 6.12.41-1-lts #1 SMP PREEMPT_DYNAMIC Fri, 01 Aug 2025
> > 20:42:03 +0000 x86_64
> > compiler info: gnuc: 15.1
> > libc info: glibc: 2.42
> > $SHELL (typically, interactive shell): /bin/bash
> >
> >
> > [Enabled Hooks]
> > prepare-commit-msg
> >
>

> Resending because I accidentally used HTML mode.
> 
> Thanks Phillip,
> 
> Sorry for replying so late. I forgot to set up notifications for this
> email address, so I had basically completely forgotten about this
> matter.

> Cheers,
> 
> Simon
> 
> 
> On Mon, 18 Aug 2025 at 23:14, Phillip Wood <phillip.wood123@gmail.com> wrote:
>>
>> Hi Simon
>>
>> On 13/08/2025 12:39, Simon Cheng wrote:
>>>
>>> What did you do before the bug happened? (Steps to reproduce your issue)
>>>
>>> 1. Initialize a git repo with `git init`
>>> 2. Install a custom `prepare-commit-msg` hook that injects some comments
>>>     - Intention: inject the output of `git log --oneline -n10` during
>>> interactive commit, so I can see past commits
>>> 3. Run `git config commit.cleanup strip`
>>>     - Intention: strip the injected comments too in non-interactive mode
>>> (e.g. `git cherry-pick` & `git rebase`)
>>> 4. Run `touch foo && git add -A && git commit -m "Initial commit"`
>>> 5. Run `touch bar && git add -A && git commit --fixup=@`
>>> 6. Run `git rebase --root --autosquash`
>>
>> Thanks for providing a simple way to reproduce this
>>
>>> What did you expect to happen? (Expected behavior)
>>>
>>> Git would perform the autosquash, while keeping the commit message of
>>> the squash target unchanged.
>>>
>>> What happened instead? (Actual behavior)
>>>
>>> Git performed the autosquash, but the commit message of the squash
>>> target is now clobbered with my injected comments.
>>
>> It looks like this stems from f7d42ceec52 (rebase -i: do leave commit
>> message intact in fixup! chains, 2021-01-28) which was added in response
>> to a bug report[1]. That commit switched from always cleaning up the
>> fixup message to never cleaning it up. I wonder if instead we should be
>> respecting the user's commit.cleanup setting. The commit message says
>> that should not respect commit.cleanup because we want to use the
>> message verbatim but that is not what we do with "pick" commands which
>> respect commit.cleanup if it is set. Given that we call the
>> prepare-commit-msg hook we cannot be sure that we're reusing the
>> original commit message verbatim anyway so I think we should probably
>> change "fixup" commands to use the same cleanup flags as "pick" commands.
>>
>> I'm going to be off the list for a week from tomorrow but I'll try and
>> look at this again when I'm back if no one else has picked it up in the
>> meantime.
>>
>> Thanks
>>
>> Phillip
>>
>> [1]
>> https://lore.kernel.org/git/CANVGpwZGbzYLMeMze64e_OU9p3bjyEgzC5thmNBr6LttBt+YGw@mail.gmail.com/
>>
>>> What's different between what you expected and what actually happened?
>>>
>>> I expected commit cleanup to happen during the autosquash. It seems
>>> like that didn't happen.
>>>
>>> Anything else you want to add:
>>>
>>> Here is my `prepare-commit-msg` script. But I expect this issue to be
>>> replicable with anything that injects comments.
>>>
>>> ```
>>> #!/usr/bin/env bash
>>> {
>>>     echo '# Last 10 commits:'
>>>     git log --oneline -n 10 --decorate=short | sed 's/^/#   /'
>>>     echo '#'
>>> } >> "$1"
>>> ```
>>>
>>> Please review the rest of the bug report below.
>>> You can delete any lines you don't wish to share.
>>>
>>>
>>> [System Info]
>>> git version:
>>> git version 2.50.1
>>> cpu: x86_64
>>> built from commit: d82adb61ba2fd11d8f2587fca1b6bd7925ce4044
>>> sizeof-long: 8
>>> sizeof-size_t: 8
>>> shell-path: /bin/sh
>>> libcurl: 8.14.1
>>> OpenSSL: OpenSSL 3.5.1 1 Jul 2025
>>> zlib-ng: 2.2.4
>>> SHA-1: SHA1_DC
>>> SHA-256: SHA256_BLK
>>> uname: Linux 6.12.41-1-lts #1 SMP PREEMPT_DYNAMIC Fri, 01 Aug 2025
>>> 20:42:03 +0000 x86_64
>>> compiler info: gnuc: 15.1
>>> libc info: glibc: 2.42
>>> $SHELL (typically, interactive shell): /bin/bash
>>>
>>>
>>> [Enabled Hooks]
>>> prepare-commit-msg
>>>
>>