Re: [PATCH 00/16] worktree: use "git reset --hard" to populate worktree

From: Eric Sunshine <sunshine@sunshineco.com>
Date: Jul 15, 2015, 06:48 UTC
Message-ID: <CAPig+cTXAdGFmq+QkNAgmHJuZgM6-Ckg_-StrTQUxmJSpX4=Qg@mail.gmail.com>
In-Reply-To: <xmqqsi8rzyzo.fsf@gitster.dls.corp.google.com>

On Mon, Jul 13, 2015 at 2:36 PM, Junio C Hamano <gitster@pobox.com> wrote:

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> Eric Sunshine <sunshine@sunshineco.com> writes:
>> This series eliminates git-checkout from the picture by instead
>> employing "git reset --hard"[2] to populate the new worktree initially.
>
> A few comments on things I noticed while reading (mostly coming from
> the original before this patch series):
>
>  - What does this comment apply to?
>
>         /*
>          * $GIT_COMMON_DIR/HEAD is practically outside
>          * $GIT_DIR so resolve_ref_unsafe() won't work (it
>          * uses git_path). Parse the ref ourselves.
>          */
>
>    It appears in front of a call to check-linked-checkout, but I
>    think the comment attempts to explain why it manually decides
>    what the path should be in that function, so perhaps move it to
>    the callee from the caller?

The placement of the comment in the original code wasn't bad, but after patch 3/16 moves code around, the comment does become somewhat confusing, so moving it to the callee seems a reasonable idea.

>  - check_linked_checkout() when trying to decide what branch is
>    checked out assumes HEAD is always a regular file, but I do not
>    think we have dropped the support of SYMLINK_HEAD yet.  It needs
>    to check st_mode and readlink(2), like resolve_ref_unsafe() does.

Hmm, I wasn't aware of SYMLINK_HEAD (and don't know if Duy was). The related code in resolve_ref_unsafe() is fairly involved, worrying about race conditions and such, however, I guess check_linked_checkout()'s implementation can perhaps be simpler, as it's probably far less catastrophic for it to give the wrong answer (or just die) under such a race?

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>  - After a new skelton worktree is set up, the code runs a few
>    commands to finish populating it, under a different pair of
>    GIT_DIR/GIT_WORK_TREE, but the function does so with setenv(); it
>    may be cleaner to use cp.env[] for it, as the process we care
>    about using the updated environment is not "worktree add" command
>    we are running ourselves, but "update-ref/symbolic-ref" and
>    "reset" commands that run in the new worktree.

After sending the series, I was realized that this could be done more cleanly with -C, but that would have to be repeated for each command, so cp.env[] might indeed be a better choice.

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> Other than that, looks nicely done.
>
> I however have to wonder if the stress on "reset --hard" on log
> messages of various commits (and in the endgame) is somewhat
> misplaced.
>
> The primary thing we wanted to see, which this series nicely brings
> us, is to remove "new-worktree-mode" hack from "checkout" (in other
> words, instead of "reset --hard", "checkout -f" would also have been
> a satisfactory endgame).

I'll see if the commit messages can be reworded a bit without becoming too wordy. ("git reset --hard" has a nice conciseness.)