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git submodule: update --remote --checkout + upstream branch change

Subject: git submodule: update --remote --checkout + upstream branch change

## tl;dr

One message between Jan 20, 2026 and Jan 20, 2026.

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D. Ben Knoble· Jan 20, 2026, 02:20 UTC · lore

On my build of git.git origin/master (with ps/history merged in, but that shouldn't affect this), I received a confusing error today:

    git submodule update --remote --checkout
    …
    Unable to find refs/remotes/origin/HEAD revision in submodule path
'…submod…'

Turns out the upstream repository had renamed the main branch from master to main, and the git dir (.git/modules/…submod…/refs/remotes/origin) still had

    ref: refs/remotes/origin/main

This is weird, because I could successfully "git fetch" inside the submodule, and "git ls-remote" showed HEAD on the remote pointing at the same place as refs/heads/main. In fact, I was so puzzled that I didn't understand where this error had come from (grepping in the source found builtin/submodule--helper.c; GIT_TRACE2=1 was not really any help here), nor did I have very high hopes of solving it except that I happened to know where to look for occurrences of "master" that might need changed.

A simple "git -C …submod… remote set-head origin -a" solves the problem; is there something the submodule code needs to do to handle this more gracefully, such as fixing it automatically or letting the user know what possible causes are? Or something I can do to avoid this coming up with other repositories I use as submodules?

-- 
D. Ben Knoble

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