FYI: There *is* actually a hacky/temporary way to use jj with submodules until proper support

[pmorch]

Hi,

I get it. Submodules support isn't here yet. #5205, #1402, #1403, #1404 and #1405. But in the meantime, using a repo that has/needs submodules is actually possible until "proper" support arrives.

E.g. I have a git repo for my hugo-based home page with a submodule for the theme in themes/ananke. I don't change the theme very often, so I'm be fine with it not being the best experience to use the submodule. E.g. I can live with having to jj git clone the submodule myself and checkout the right version.

I tried that:

$ cd themes
$ jj git clone https://github.com/theNewDynamic/gohugo-theme-ananke.git ananke
$ cd ananke
$ jj new 3fc0dba

And as far as I can see, it works "fine" enough for me. Yes, if I make changes to the theme (which I don't) I wont see them. Yes, I need to manually see and/or modify any submodule configuration using git.

But it doesn't preclude me from using jj. Just saying.

The main missing thing: Is there a way to see from jj that I need version 3fc0dba of themes/ananke? I can see the path and url from .gitmodules, but not the version. Because then I could write a jj-submodule-init-update.py script 🙂.

Are there any problems with this that I've overlooked?

[pmorch]

About the missing piece: We can find that themes/ananke has been checked out at 3fc0dba with:

$ jj log -r :: --limit 1 --patch --git themes/ananke                                                
◆  tsmpzlso [email protected] 2025-03-23 00:07:59 ebde216d
│  Went back to an older ananke version to show 'All Posts' again
│  diff --git a/themes/ananke b/themes/ananke
│  index 8e3303d0a4..3fc0dba401 040000

$ jj log -r :: --limit 1 --patch --git themes/ananke | grep '^.  index ' | sed 's/.*\.\.//; s/ .*//' 
3fc0dba401

So now, if I wasn't so lazy, I could actually write a jj-submodule-init-update.py script 🙂

[ravicious]

Thanks for the writeup! I gave it a try and it seems to work.

I use colocated repos, both the main repo and the submodule were cloned with jj git clone --colocate. For some reason, the jj log you posted does not return the right commit for me or maybe I misunderstood what you wanted to achieve.

What I needed is a way to bring the submodule up to whatever the main repo currently points to. The commit in the submodule that the submodule ref in the main repo currently points to can be extracted with git ls-tree --object-only HEAD -- "$SUB" where $SUB is the path to the submodule.

I wrote this zsh function to help me update the submodule:

function update-jj-submodule() {
  local SUB=$1
  local COMMIT=$(git ls-tree --object-only HEAD -- "$SUB")
  if [[ -z "$COMMIT" ]]; then
    echo "No target commit found for $SUB"
    return 1
  fi
  jj git fetch --repository "$SUB" && \
  jj new "$COMMIT" --repository "$SUB"
}

Usage is just update-jj-submodule <path to submodule>.