[RFC] worktree: add --recurse-submodules support to git worktree add

3 messages between Apr 15, 2026 and Apr 15, 2026, from JAM, Phillip Wood, Junio C Hamano.

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JAMApr 15, 2026, 00:14 UTC on lore

Back in 2022, Glen Choo noted [1] that git worktree add leaves submodules unhandled and suggested a --recurse-submodules flag to fix that. The thread went quiet. The 2015–2016 discussions by Duy and Beller [2][3] had flagged a deeper design concern: submodule existence (which worktrees have which submodules checked out) is tangled up with submodule configuration (URL, path), making per-worktree submodule support tricky to reason about.

This proposal sidesteps that concern entirely. Rather than touching submodule configuration at all, the idea is to reuse the git object data that's already present in the main repository — the same thing git worktree add already does for the top-level object store, extended down to the submodule layer.

The use case has also grown more pressing: multi-agent development workflows (where several autonomous coding agents work concurrently on different branches of the same repository) rely heavily on worktrees for isolation, and fall apart on projects with submodules.

Concretely, git worktree add --recurse-submodules would:

1. Hardlink $GIT_COMMON_DIR/modules/ into the new worktree's entry.
Independent directory trees, shared inodes — no extra disk, no network.
2. Rewrite core.worktree in the hardlinked config and config.worktree
files to point at the new worktree's working directory instead of the main
repo's.
3. Run git submodule update inside the new worktree to write the .git
pointer files into each submodule directory. Entirely local since the
modules directory is already there.
4. Populate working trees with git read-tree HEAD && git checkout -- . per
submodule, since the hardlinked index files start empty.

A shell script implementing this as a prototype is attached.

The worktreeConfig extension case (step 2) is the one place that needs care, since core.worktree may live in either config or config.worktree depending on the submodule. The prototype handles both. The other open question is policy for submodules not yet initialized in the main repo — skip silently, warn, or error out.

Would there be interest in a proper patch series for this?

[1] https://lore.kernel.org/git/kl6lwnimyxbq.fsf@chooglen-macbookpro.roam.corp.google.com/ [2] https://lore.kernel.org/git/CACsJy8D8Ur4W348t-WFUPrb7SQxmff5MJ4aRp+w+ZiQ7VVvipg@mail.gmail.com/ [3] https://lore.kernel.org/git/CAGZ79kZB8U+ERNeYpZ-i7Ldip7xbz0ND53g4bzMkzFC3pnyv+w@mail.gmail.com/

Signed-off-by: Jimmy Aguilar kratsbinovish@gmail.com

Phillip WoodApr 15, 2026, 14:05 UTC in reply to JAM on lore

Re: [RFC] worktree: add --recurse-submodules support to git worktree add

On 15/04/2026 01:14, JAM wrote:

Show 15 quoted lines

> Back in 2022, Glen Choo noted [1] that git worktree add leaves submodules
> unhandled and suggested a --recurse-submodules flag to fix that. The thread
> went quiet. The 2015–2016 discussions by Duy and Beller [2][3] had flagged a
> deeper design concern: submodule existence (which worktrees have which
> submodules checked out) is tangled up with submodule configuration (URL, 
> path),
> making per-worktree submodule support tricky to reason about.
> 
> This proposal sidesteps that concern entirely. Rather than touching 
> submodule
> configuration at all, the idea is to reuse the git object data that's 
> already
> present in the main repository — the same thing git worktree add already 
> does
> for the top-level object store, extended down to the submodule layer.

I'm not really a submodule user so maybe I'm missing something. Worktrees separate out per-worktree data such as refs like HEAD which are stored under the worktree's gitdir in "$GIT_COMMON_DIR/worktrees/$id" and per-repository data such as the object store which is stored under "$GIT_COMMON_DIR". The proposal below appears to use the same modules directory for each worktree so if I have two worktrees A and B each with a submodule "sub" how can I checkout commit C1 in "A/sub" and commit C2 in "B/sub" when they share the same gitdir? It makes sense for "A/sub" and "B/sub" to share the same object database, but they don't want to share the same HEAD.

Thanks

Phillip

Show 47 quoted lines

> 
> The use case has also grown more pressing: multi-agent development workflows
> (where several autonomous coding agents work concurrently on different 
> branches
> of the same repository) rely heavily on worktrees for isolation, and 
> fall apart
> on projects with submodules.
> 
> Concretely, git worktree add --recurse-submodules would:
> 
> 1. Hardlink $GIT_COMMON_DIR/modules/ into the new worktree's entry.
> Independent directory trees, shared inodes — no extra disk, no network.
> 2. Rewrite core.worktree in the hardlinked config and config.worktree
> files to point at the new worktree's working directory instead of the main
> repo's.
> 3. Run git submodule update inside the new worktree to write the .git
> pointer files into each submodule directory. Entirely local since the
> modules directory is already there.
> 4. Populate working trees with git read-tree HEAD && git checkout -- . per
> submodule, since the hardlinked index files start empty.
> 
> A shell script implementing this as a prototype is attached.
> 
> The worktreeConfig extension case (step 2) is the one place that needs care,
> since core.worktree may live in either config or config.worktree
> depending on the submodule. The prototype handles both. The other open 
> question
> is policy for submodules not yet initialized in the main repo — skip 
> silently,
> warn, or error out.
> 
> Would there be interest in a proper patch series for this?
> 
> [1] https://lore.kernel.org/git/kl6lwnimyxbq.fsf@chooglen- 
> macbookpro.roam.corp.google.com/ <https://lore.kernel.org/git/ 
> kl6lwnimyxbq.fsf@chooglen-macbookpro.roam.corp.google.com/>
> [2] https://lore.kernel.org/git/CACsJy8D8Ur4W348t- 
> WFUPrb7SQxmff5MJ4aRp+w+ZiQ7VVvipg@mail.gmail.com/ <https:// 
> lore.kernel.org/git/CACsJy8D8Ur4W348t- 
> WFUPrb7SQxmff5MJ4aRp+w+ZiQ7VVvipg@mail.gmail.com/>
> [3] https://lore.kernel.org/git/CAGZ79kZB8U+ERNeYpZ- 
> i7Ldip7xbz0ND53g4bzMkzFC3pnyv+w@mail.gmail.com/ <https:// 
> lore.kernel.org/git/CAGZ79kZB8U+ERNeYpZ- 
> i7Ldip7xbz0ND53g4bzMkzFC3pnyv+w@mail.gmail.com/>
> 
> Signed-off-by: Jimmy Aguilar kratsbinovish@gmail.com 
> <mailto:kratsbinovish@gmail.com>

Junio C HamanoApr 15, 2026, 16:23 UTC in reply to Phillip Wood on lore

Re: [RFC] worktree: add --recurse-submodules support to git worktree add

Phillip Wood <phillip.wood123@gmail.com> writes:

Show 27 quoted lines

> On 15/04/2026 01:14, JAM wrote:
>> Back in 2022, Glen Choo noted [1] that git worktree add leaves submodules
>> unhandled and suggested a --recurse-submodules flag to fix that. The thread
>> went quiet. The 2015–2016 discussions by Duy and Beller [2][3] had flagged a
>> deeper design concern: submodule existence (which worktrees have which
>> submodules checked out) is tangled up with submodule configuration (URL, 
>> path),
>> making per-worktree submodule support tricky to reason about.
>> 
>> This proposal sidesteps that concern entirely. Rather than touching 
>> submodule
>> configuration at all, the idea is to reuse the git object data that's 
>> already
>> present in the main repository — the same thing git worktree add already 
>> does
>> for the top-level object store, extended down to the submodule layer.
>
> I'm not really a submodule user so maybe I'm missing something. 
> Worktrees separate out per-worktree data such as refs like HEAD which 
> are stored under the worktree's gitdir in 
> "$GIT_COMMON_DIR/worktrees/$id" and per-repository data such as the 
> object store which is stored under "$GIT_COMMON_DIR". The proposal below 
> appears to use the same modules directory for each worktree so if I have 
> two worktrees A and B each with a submodule "sub" how can I checkout 
> commit C1 in "A/sub" and commit C2 in "B/sub" when they share the same 
> gitdir? It makes sense for "A/sub" and "B/sub" to share the same object 
> database, but they don't want to share the same HEAD.

True. I am not a submodule user and do not have a strong interest in submodules, but I agree that once the superproject wants to use multiple worktrees, the submodules bound to it inevitably need to use different worktrees that correspond to the worktrees used by the superproject exactly because of the point you raise here. They need to be able to independently check out a suitable commit in the context of the superproject's worktree that is checked out.