Re: [PATCH v2] branch: report active bisect run when rejecting delete

René Scharfe [off-list ref] writes:

git branch refuses to delete branches that are currently checked out
with a message like this: "error: cannot delete branch 'foo' used by
worktree at '/path/of/worktree'".  This can be confusing if it's an
internal checkout for git bisect.  Report a more specific error in
that case to help users that might have forgotten their bisect run.

Suggested-by: stsp <redacted>
Signed-off-by: René Scharfe <redacted>
---
Changes since v2:
- Only report bisect runs as specific rejection reason for now.
- Leave rebasing unaddressed because I don't see how to formulate
  clear and readable messages for those scenarios, yet.
- Collect all checkout reasons of all branches in a simple array for
  easy use, e.g. to eventually address rebases or for git status.
- Rebased onto the landed test_grep conversion.

The scope of this patch has shrunk a bit.  While the 'in use by a
rebase' state is still recognized internally, unlike in the previous
round, we guard users only against the 'in use by a bisect' state and
the 'in use by being checked out' state.

This is probably a good single step, so unless there are objections,
let's mark the topic for 'next'.

My understanding of what is stopping us from taking the next step is
that we do not know the exact phrasing to express the 'in use by a
rebase' state concisely.

Thanks.