Preserve a remote reference for merged MRs
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Proposal
At the moment, it can be difficult to reliably correlate commits that land in a branch to the commits that were in the merge request. This is because commits can be mutated as they land, chiefly due to squash merges. This can cause difficult-to-solve problems; for example:
- reliably identifying MRs that commits came from (e.g. #22694)
- identifying commits for cherry-picking across branches (e.g.
git cherry) - even identifying whether specific commits have landed (e.g.
git branch --contains)
Today, gitlab maintains one or two long-lived refs for each MR:
-
refs/merge-requests/:iid/head(the head of the MR branch) -
refs/merge-requests/:iid/merge(if using merge pipelines, the merge commit)
There's also a short-lived one refs/merge-requests/:iid/train to close a merge-train race condition.
My proposal is to add a third long-lived MR ref, refs/merge-requests/:iid/completed which points at the post-merge merge commit (post-squash) (or the last commit in the branch, if the fast-forwarding). I'm not tied to completed, I probably would have used merged if merge wasn't already in use.
Some examples of commands that I'd like to work (assume for these examples I have this fetch refspec in .git/config: fetch = +refs/merge-requests/*:refs/remotes/origin/mr/*) (forgive me for minor errors here, I'm writing them in this buffer)
- List MRs that have landed on a branch:
completed=($(git branch --merged origin/develop | grep 'mr/.*/completed' | cut -d / -f 2 ))) - Retrieve original commits given an mr:
for i in "${completed[@]}; do git diff $(git merge-base origin/develop mr/$i/head)..mr/$i/head - find downstream branches from the landed MR:
git branch -r --contains mr/12345/completed