Backport Skill

Invocation

This skill can be triggered in two ways:

• From a PR with backport labels: provide a PR number and the skill will read the backport stable/<X> labels to determine target branches.
• Explicitly: provide a PR number and a specific list of target branches (e.g. "backport #3697 to stable/2024.1 and stable/2023.2").

Workflow

1. Understand the change

Fetch the full diff of the original PR. Read and understand what the change does — which files are modified, what is being added or removed, and what component behaviour it affects. This understanding is essential for making good judgements during conflict resolution and compatibility checks later.

2. Determine target branches

If target branches are not explicitly provided, read the PR's backport stable/<X> labels. Then check comments from vexxhost-bot to identify which branches already have an open or merged backport PR — skip those. Sort the remaining branches newest first (e.g. stable/2025.1 before stable/2024.2 before stable/zed).

Also record whether the original PR has labels that the automated workflow would copy to backport PRs. Mirror .github/workflows/backports.yaml copy_labels_pattern; currently, copy skip-release-notes when it exists on the original PR so reno checks do not require a release note for note-exempt changes.

3. Process branches one by one (cascade strategy)

Use a cascade strategy: cherry-pick onto the newest branch first, fix any conflicts there, then use that fixed commit as the source for the next-older branch. This means conflicts only need to be resolved once and the fix propagates naturally through older branches.

For the first branch, cherry-pick the original merged commit from main:

git fetch origin <branch>
git worktree add -d .worktree/backport-<PR>-to-<slug> origin/<branch>
cd .worktree/backport-<PR>-to-<slug>
git switch --create backport-<PR>-to-<branch>
git cherry-pick -x <original-sha>

For each subsequent branch, cherry-pick from the previous branch's commit:

PREV=$(git -C .worktree/backport-<PR>-to-<prev-slug> rev-parse HEAD)
git cherry-pick -x $PREV

Branch slug convention: replace / with . in worktree directory names (e.g. stable/2025.1 → .worktree/backport-<PR>-to-stable-2025.1) but keep / in the git branch name itself.

4. Assess compatibility before applying

Before applying (or after a conflict surfaces), compare the diff being applied against the state of the target branch. Ask: does this change make sense for this branch as-is? Consider things like:

• Does the branch have the required dependency or component version for this change to function?
• Are the files being patched present and structurally similar enough?

If the change cannot work on the target branch without a prerequisite that is absent, skip the branch and clearly note why (so the user can act on it later).

5. Resolve conflicts

If git cherry-pick fails, inspect the conflicts. Use the understanding of the change (from step 1) and the state of the target branch to resolve them thoughtfully. The goal is to produce a result that correctly applies the intent of the original change to the target branch — not to mechanically accept one side or the other.

After resolving all conflicts:

git add <resolved-files>
git cherry-pick --continue --no-edit

6. Validate

After each successful cherry-pick, run pre-commit across the range of the cherry-picked commit:

pre-commit run --from-ref HEAD~1 --to-ref HEAD

Any hook failures that are unrelated to the files touched by the backport should be ignored. Investigate and fix any failures that are caused by the backported changes before pushing.

7. Push and open a PR

If the original PR has skip-release-notes, pass that label to every backport PR:

COPY_LABEL_ARGS=()
if gh pr view <PR> --repo vexxhost/atmosphere --json labels --jq '.labels[].name' | grep -qx 'skip-release-notes'; then
  COPY_LABEL_ARGS+=(--label skip-release-notes)
fi

git push origin backport-<PR>-to-<branch>

gh pr create \
  --repo vexxhost/atmosphere \
  --base <branch> \
  --head backport-<PR>-to-<branch> \
  --title "[Backport <branch>] <original PR title>" \
  --body "# Description\nBackport of #<PR> to \`<branch>\`." \
  "${COPY_LABEL_ARGS[@]}"

8. Clean up

After all PRs are created, remove all worktrees:

git worktree remove --force .worktree/backport-<PR>-to-<slug>

Reporting

Finish with a summary table covering every branch that was labeled, including skipped ones:

Branch	PR	Notes
stable/2025.1	#NNNN	✅ Created
stable/2024.2	#NNNN	✅ Clean apply
stable/zed	—	⏭️ Skipped — requires prerequisite #NNNN first