squashWip does not work with git 2.19.x

[gregorriegler]

squashWip (mob done --squash-wip) does an interactive rebase which fails if you use git 2.19.x or lower

=== RUN   TestStartDoneSquashWipWithUnpushedCommit
    mob_test.go:1589: Creating testbed in temporary directory /tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001
    mob_test.go:1589:   git --bare init
    mob_test.go:1589:   git symbolic-ref HEAD refs/heads/master
    mob_test.go:1589:   git clone --origin origin file:///tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/remote .
    mob_test.go:1589:   git config --local user.name local
    mob_test.go:1589:   git config --local user.email local@example.com
    mob_test.go:1589:   git checkout -b master
    mob_test.go:1589:   git add .
    mob_test.go:1589:   git commit -m "initial import"
    mob_test.go:1589:   git push --set-upstream --all origin
    mob_test.go:1589:   git clone --origin origin file:///tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/remote .
    mob_test.go:1589:   git config --local user.name localother
    mob_test.go:1589:   git config --local user.email localother@example.com
    mob_test.go:1589:   git clone --origin origin file:///tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/remote .
    mob_test.go:1589:   git config --local user.name alice
    mob_test.go:1589:   git config --local user.email alice@example.com
    mob_test.go:1589:   git clone --origin origin file:///tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/remote .
    mob_test.go:1589:   git config --local user.name bob
    mob_test.go:1589:   git config --local user.email bob@example.com
    mob_test.go:1589:   git clone --origin origin file:///tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/remote .
    mob_test.go:1589:   git config --local user.name local-symlink
    mob_test.go:1589:   git config --local user.email local-symlink@example.com
    mob_test.go:1589: 
        ===== cd /tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/local
    mob_test.go:1589:   git add file1.txt
    mob_test.go:1589:   git commit -m not a mob session yet
    mob_test.go:1589: 
        ===== cd /tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/alice
    mob_test.go:1589:   git fetch origin --prune
    mob_test.go:1589:   git merge FETCH_HEAD --ff-only
    mob_test.go:1589: > starting new session from origin/master
    mob_test.go:1589:   git checkout -B mob-session origin/master
    mob_test.go:1589:   git push --no-verify --set-upstream origin mob-session
    mob_test.go:1589: > you are on wip branch 'mob-session' (base branch 'master')
    mob_test.go:1589:   git add --all
    mob_test.go:1589:   git commit --message mob next [ci-skip] [ci skip] [skip ci]
    mob_test.go:1589:   
    mob_test.go:1589:   lastFile:file2.txt --no-verify
    mob_test.go:1589:     file2.txt | 1 +
    mob_test.go:1589:     1 file changed, 1 insertion(+)
    mob_test.go:1589:     538970d6da1639808e7402e084ebca496dc74318
    mob_test.go:1589:   git push --no-verify origin mob-session
    mob_test.go:1589:   git checkout master
    mob_test.go:1589: 
        ===== cd /tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/local
    mob_test.go:1589:   git push
    mob_test.go:1589: 
        ===== cd /tmp/TestStartDoneSquashWipWithUnpushedCommit379541793/001/alice
    mob_test.go:1589:   git fetch origin --prune
    mob_test.go:1589:   git merge FETCH_HEAD --ff-only
    mob_test.go:1589: > joining existing session from origin/mob-session
    mob_test.go:1589: ⚠ Careful, your wip branch (mob-session) diverges from your main branch (origin/master) !
    mob_test.go:1589:   git checkout -B mob-session origin/mob-session
    mob_test.go:1589:   git branch --set-upstream-to=origin/mob-session mob-session
    mob_test.go:1589: > you are on wip branch 'mob-session' (base branch 'master')
    mob_test.go:1589: 538970d 0 seconds ago <alice>
    mob_test.go:1589:   git fetch origin --prune
    mob_test.go:1589: > rewriting history of 'mob-session': squashing wip commits while keeping manual commits.
    mob_test.go:1589: ERROR git rebase --interactive --keep-empty 4cbf4e0058d2852fa7b42aa071b8d3e22cb7ccc4
    mob_test.go:1589: ERROR error: could not open '.git/rebase-merge/git-rebase-todo': No such file or directory
    mob_test.go:1589: ERROR fatal: reference is not a tree: 4cbf4e0058d[2852](https://github.com/remotemobprogramming/mob/actions/runs/3244504219/jobs/5320767891#step:7:2853)fa7b42aa071b8d3e22cb7ccc4
    mob_test.go:1589: ERROR could not detach HEAD
    mob_test.go:1589: ERROR exit status 1
exit status 1
FAIL	github.com/remotemobprogramming/mob/v4	17.232s

since it works with git 2.20.0 I tried to find out what has changed in that version:
git 2.20.0 changelog https://github.com/git/git/blob/master/Documentation/RelNotes/2.20.0.txt

• "git rebase -i" learned a new insn, 'break', that the user can
  insert in the to-do list. Upon hitting it, the command returns
  control back to the user.
• "git rebase" and "git rebase -i" have been reimplemented in C.

[simonharrer]

This option is probably used by people that keep their git up to date. :-) I assume that 99.9% of the mob user base doesn't use this feature, and that's why this hasn't been reported yet.

[hollesse]

I think so too. This feature is rarely used and git 2.19 was release in 2018. Therefore I will close this issue.