Re: Git submodule update remote keeps using previous default branch

From: Bryan Turner <bturner@atlassian.com>
Date: Oct 15, 2021, 09:05 UTC
Message-ID: <CAGyf7-HZirxc0qoD1u9a3jx4egsjq=-Mdy_HCf2o-oWBrdUX+A@mail.gmail.com>
In-Reply-To: <CAA1vfca+kPSsitsZad-bmrd+o1ay60NXZrH2zGLpwN69Px-rtw@mail.gmail.com>

On Fri, Oct 15, 2021 at 1:35 AM Sjoerd Langkemper <sjoerd-2021@linuxonly.nl> wrote:

Show 21 quoted lines

>
> I am having trouble with git 2.33.1 checking out the wrong branch for
> submodules for which the default branch has changed. `git submodule
> update --remote` seems to remember the branch name to retrieve, while
> I expect it to use the remote HEAD every time. This causes unexpected
> behaviour when the remote HEAD starts pointing to another branch.
>
> I create a new git project and add a submodule, with `git submodule
> add git@host:foo/testproject.git`.
>
> This checks out the default branch, `master` in this case. `git remote
> show origin` also shows that `master` is the HEAD branch. Running `git
> submodule update --remote` updates the submodule to the latest master.
>
> Now I change the default branch on the remote (using Gitlab's web
> interface) to `newmaster`.
>
> `git remote show origin` now correctly shows `newmaster` as the
> remote's HEAD branch. However, running `git submodule update --remote`
> still updates the submodule to the latest `master` branch, while I
> expect it to update to the lastest `newmaster` branch.

I suspect this is going to be the same answer I gave on the last thread about submodules[1]. Submodules in Git store the _commit ID_ they point to in the tree, but they do not store a _ref name_, nor do they have some indicator for "It was the default branch". They choose a ref by (essentially) looping over the refs from the remote (which are always sent in alphabetical order) and choosing the first one with a matching SHA. If your "newmaster" is alphabetically after "master", and "master" still exists, and both refs point to the same commit (or only "master" points to it), I suspect your submodule is going to choose that.

[1] https://lore.kernel.org/git/CAGyf7-FAHJOb6iQYqYNt0WSk+zUHUJ_FjrU1xis1bBQd9Z6KPQ@mail.gmail.com/

Show 7 quoted lines

>
> There's no branch specified in .gitmodules or .git/config. I am not
> sure how git remembers the branch. When switching `testproject` to
> `newmaster` manually and then running `git submodule update --remote`,
> it is reset to `master` again.
>
> Is this a bug? Can I change the branch somehow?

If you updated the submodule to reference a commit that was on "newmaster" and not present on "master", I think it'd change.

>
> Regards,
>
> Sjoerd Langkemper