Subject: Re: New orphan worktree?

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Tue, 23 Feb 2021 01:17:05 +0100

On Tue, Feb 23 2021, Eric Sunshine wrote:

> On Mon, Feb 22, 2021 at 4:45 AM Ævar Arnfjörð Bjarmason
> <[email-masked]> wrote:
>> On Sun, Feb 21 2021, Eric Sunshine wrote:
>> > Rather than making --orphan a boolean flag, we'd probably want to
>> > mirror the behavior of the other commands and have <branch> be an
>> > argument consumed by --orphan:
>> >
>> >     git worktree add --orphan <branch> <path>
>> >
>> > That would make --orphan, -b, and -B mutually exclusive, much like
>> > they are for git-checkout, and much like -c, -C, and --orphan are
>> > mutually exclusive for git-switch.
>>
>> I see now (but didn't before, I haven't really used "switch" before)
>> that that's how it works.
>>
>> But that doesn't seem to make much sense as a UI, maybe I'm missing
>> something but how do you:
>>
>>     git switch --orphan existing-branch
>>
>> Just like you can:
>>
>>     git switch -C existing-branch <start-point>
>
> When responding to your initial email, I noticed this same shortcoming
> of --orphan in both git-branch and git-switch, and assumed that's why
> you made it a boolean in combination with -b/-B in "git worktree add".
> Before writing that email, I did put a bit of thought into how one
> might support a "force" mode but didn't include my thoughts in the
> message.
>
>> It's actually this exact use-case that prompted me to write the --orphan
>> patch. I wanted to create a "meta" orphan branch in my git.git, but had
>> an existing local "meta" (from Jeff King) that I'd happened to have
>> checked out long ago which I first needed to "git branch -D".
>>
>> Wouldn't it make more sense for a feature like this & back-compat to
>> start with switch's "--orphan" implying "-c", but you could also supply
>> "--orphan -C" instead? And in worktree have -b and -B work like they do
>> for other branches.
>
> I'm not sure I follow. In git-switch, --orphan does not imply -c even
> though --orphan also creates a new branch (thus seems to work similar
> to -c); it is nevertheless mutually-exclusive with -c and -C. The same
> goes for --orphan in git-branch.

I think we're on the same page with regards to what I meant. I.e. I
don't see how it makes sense to conflate the type of branch we want
(orphan or not orphan) with whether we want to clobber that branch or
not (switch -c or -C, or worktree -b or -B)

> As far as combining --orphan and -C (or -c), I'm not sure how we would
> arrange that using the existing parse_options() mechanism. It seems
> too magical and has potential for weird corner cases.

Isn't it just having --orphan be an OPTION_STRING with
PARSE_OPT_LASTARG_DEFAULT. I.e. to support:

    git switch -b branch --orphan
    git switch -B branch --orphan
    git switch --orphan branch

And:

    git worktree add -b branch --orphan
    git worktree add -B branch --orphan

I didn't test it, just skimmed the code.

> Since git-worktree doesn't yet support --orphan, we certainly have
> more leeway and could go with your proposal of having --orphan be
> boolean and always requiring it to be used in conjunction with -b/-B.
> However, I'm quite hesitant to take that approach since it breaks with
> existing precedent in git-branch and git-switch, in which case
> --orphan takes its own argument (<branch>) and is mutually-exclusive
> with -b/-B/-c/-C.

In git-branch? Isn't it only git [checkout|switch] that takes --orphan?

But yeah, I agree that it makes sense for "worktree add" to be
consistent with "switch". I was just wondering if we couldn't fix what
seems to me to be a small options UI issue while we're at it.

> When I was pondering the issue before writing my original response,
> two thoughts came to mind. (1) "git worktree add --force --orphan
> <branch>" would be one way to make your case work; (2) given how
> infrequently --orphan is used, we just punt and require people to
> first use "git branch -D <branch>" if necessary (which has been the
> status-quo for git-branch and git-switch). The latter thought is
> superficially tempting, though it doesn't help in automation
> situations since "git branch -D <branch>" errors out if <branch>
> doesn't exist, so a script would first have to check for existence of
> <branch> before attempting to delete it prior to using "git worktree
> add --orphan <branch>".

I think not having a -B or -C equivalent at all would be preferrable to
having a --force special-case just to work around the lack of it for
--orphan.