Re: [PATCH] git-new-workdir: support submodules

From: Craig Silverstein <csilvers@khanacademy.org>
Date: Dec 23, 2014, 21:51 UTC
Message-ID: <CAGXKyzHoLLgkXk0X4UVtLBEryqsHriKmmO5+2iVWk3mR8y7=Hw@mail.gmail.com>

[Ack, I forgot to cc myself on the original patch so now I can't reply to it normally. Hopefully my workaround doesn't mess up the threading too badly.]

Junio C Hamano <gitster <at> pobox.com> writes:

Show 18 quoted lines

>
> Hmmmm, does that mean that the submodule S in the original
> repository O's working tree and its checkout in the secondary
> working tree W created from O using git-new-workdir share the same
> repository location?  More specifically:
>
>     O/.git/                 - original repository
>         O/.git/index            - worktree state in O
>         O/S                     - submodule S's checkout in O
>         O/S/.git                - a gitfile pointing to O/.git/modules/S
>     O/.git/modules/S        - submodule S's repository contents
>         O/.git/modules/S/config - submodule S's config
>
>     W/.git/                 - secondary working tree
>         W/.git/config           - symlink to O/.git/config
>         W/.git/index            - worktree state in W (independent of O)
>     W/S                     - submodule S's checkout in W (independent of O)
>     W/S/.git                - a gitfile pointing to O/.git/modules/S

Right until the last line. The .git file holds a relative path (at least, it always does in my experience), so W/S/.git will point to W/.git/modules/S.

Also, to complete the story, my changes sets the following:

        W/.git/modules/S    - secondary working tree for S
             W/.git/modules/S/config   - symlink to O/.git/modules/S/config
             W/.git/modules/S/index    - worktree state in W's S
(independent of O and O's S)

> Doesn't a submodule checkout keep some state tied to the working
> tree in its repository configuration file?

Do you mean, in 'config' itself?  If so, I don't see it.  (Though it's
possible there are ways to use submodules that do keep working-tree
state in the config file, and we just happen not to use those ways.)
Here's what my webapp/.git/modules/khan-exercises/config looks like:
---
[core]
        repositoryformatversion = 0
        filemode = true
        bare = false
        logallrefupdates = true
        worktree = ../../../khan-exercises
[remote "origin"]
        url = http://github.com/Khan/khan-exercises.git
        fetch = +refs/heads/*:refs/remotes/origin/*
[branch "master"]
        remote = origin
        merge = refs/heads/master
        rebase = true
[submodule "test/qunit"]
        url = https://github.com/jquery/qunit.git
--

The only thing that seems vaguely working-tree related is the 'worktree' field, which is the field that motivated me to set up my patch the way it is.

> Wouldn't this change
> introduce problems by sharing O/.git/modules/S/config between the
> two checkouts?

It's true that this change does result in sharing that file, so if that's problematic then you're right. I'm afraid I don't know all the things that can go into a submodule config file.

(There are other things I don't know as well, such as: do we see .git files with 'gitdir: ...' contents only for submodules, or are there other ways to create them as well? Are 'gitdir' paths always relative? Are there special files in .git (or rather .git/modules/S) that exist only for submodules and not for 'normal' repos, that we need to worry about symlinking? I apologize for not knowing all these git internals, and hope you guys can help point out any gaps that affect this patch!)

craig