We recently converted both the `git rebase` and the `git rebase -i`
command from Unix shell scripts to builtins.
The former has a safety valve allowing to fall back to the scripted
`rebase`, just in case that there is a bug in the builtin `rebase`:
setting the config variable `rebase.useBuiltin` to `false` will
fall back to using the scripted version.
The latter did not have such a safety hatch.
Let's reinstate the scripted interactive rebase backend so that `rebase.useBuiltin=false` will not use the builtin interactive rebase,
just in case that an end user runs into a bug with the builtin version
and needs to get out of the fix really quickly.
This is necessary because Git for Windows wants to ship the builtin
rebase/interactive rebase earlier than core Git: Git for Windows
v2.19.0 will come with the option of a drastically faster (if a lot
less battle-tested) `git rebase`/`git rebase -i`.
As the file name `git-rebase--interactive` is already in use, let's
rename the scripted backend to `git-legacy-rebase--interactive`.
A couple of additional touch-ups are needed (such as teaching the
builtin `rebase--interactive`, which assumed the role of the
`rebase--helper`, to perform the two tricks to skip the unnecessary
picks and to generate a new todo list) to make things work again.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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