git submit doesn't like it when commits have 2+ branches

[claytonrcarter]

Description of the bug

git submit behaves strangely when a commit has 2 branches pointing at it. From what I can tell, it just skips the commit entirely, though the implementation¹ suggests that it may depend on the order in which the branches are processed by submit.

Repro:

touch test-file.txt
git add test-file.txt
git commit -m 'temp'
git branch test-1
git submit
# this should report:
# Skipped 1 branch (not yet on remote): test-1

git branch test-2
git submit
# uh oh, this reports nothing! 😱 

This seems to also "work" if one of the branches is already pushed, and a new branch is added.

I haven't actually encountered this in the wild, but I ran into it while pushing some of my recent PRs, when I unstacked a bunch of commits and assigned them each a branch to push independently. I accidentally doubled up one of them ... et voila.

Expected behavior

I expect it push all branches, or all applicable branches is some but not all of them exist on the remote.

Actual behavior

The multi-branch commits are just skipped.

Version of rustc

rustc 1.71.0 (8ede3aae2 2023-07-12)

Automated bug report

n/a

Version of git-branchless

master

Version of git

git version 2.41.0

Footnotes

1. https://github.com/arxanas/git-branchless/blob/master/git-branchless-submit/src/branch_forge.rs#L135-L183 ↩

[arxanas]

I don't think this depends on the branch ordering. If there is more than one branch pointing to the same commit, then it will trigger that code path.

IIRC the main thing I was worried about was if one of the branches was a long-lived branch like main. This could happen if you create a branch off of main, intending to start work, and then run git submit for some reason. It would be quite bad if you also force-pushed the main branch! (Maybe there's a check/exclusion for the main branch already?)

Obviously there should be some kind of diagnostic in this case.