Re: [PATCH][OUTREACHY] bisect: allow `git bisect` to run from subdirectory

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi Junio,

On Wed, 21 Oct 2020, Junio C Hamano wrote:

> Taylor Blau <me@ttaylorr.com> writes:
>
> > I'm not sure that that's the case: Junio pointed out a while[1] ago that
> > we'd have to answer the question of "what happens if I'm in a
> > subdirectory that goes away during some point of the bisection?". I
> > think that you could probably find an answer to that question, but the
> > fact that there isn't an obvious one seems to indicate that we're going
> > down the wrong path.
> >
> > I agree that it would be nice to run bisect from any directory, but it
> > may not be as easy as I'd hope.
>
> True.
>
> I would not mind all that much a single "git checkout ancient" that
> makes the $cwd go away and confuse the user.  But a bisect session
> would jump around versions randomly (eh, logarithmically?) and you'd
> end up switching out of a version in a non-existing $cwd to another
> version that has the directory (created internally by mkdir(2)), and
> I'm fairly certain that your phantom $cwd that is not connected to
> any other filesystem entity and the directory that should be at the
> same path in the newly checked-out version are different filesystem
> entities.  I'd rather not have to think about the interaction
> between git and the system after that point.

By that token, we should also prevent `git rebase` from running in a
subdirectory, but we don't.

Besides, this only becomes an issue when the directory becomes _empty_
(including untracked files) because we don't remove it otherwise.

I am actually more worried about bisecting between revisions that replace
the current subdirectory by a symlink or something.

But again, this is pretty much precisely the kind of scenario that we
_already_ allow running into with `git rebase`. So I see little point
refusing `git bisect` users to run in a subdirectory.

I know that _I_ often grumble after `git bisect start` fails, then try to
pull out the last remains of my patience and insert `-C ..` or `-C ../..`
between `git` and `bisect` and _still_ get what I want, all while shaking
my imaginary fist at `git bisect` for forcing me to type those extra
keystrokes.

Ciao,
Dscho