| name | merge-upstream |
| description | Sync a fork branch with an upstream remote using a history-preserving merge. Use this whenever the user says /merge-upstream, merge upstream, sync upstream, sync fork, or wants upstream changes integrated without rebasing or force-pushing. |
Merge Upstream
Sync the current fork branch with upstream/<branch> using a merge commit by default. Preserve local commit hashes, keep push non-destructive, and never rewrite history.
Usage
Treat these as equivalent triggers:
/merge-upstream [--base=<branch>] [--ff-allow]
merge upstream [--base=<branch>] [--ff-allow]
sync fork with upstream
Options:
--base=<branch>: use that upstream branch instead of auto-detecting the upstream default branch.--ff-allow: allow git merge --ff-only when the current branch has no unique local commits. Without this, use git merge --no-ff to leave an explicit sync commit.
Invariants
- Do not run
git rebase.
- Do not run
git push --force or git push --force-with-lease.
- Do not run
git stash push -a.
- Do not bypass hooks or signing with
--no-verify or --no-gpg-sign.
- Ask before pushing.
Workflow
-
Validate the repository:
git rev-parse --is-inside-work-tree
git branch --show-current
git remote get-url upstream
git remote get-url origin
Abort on detached HEAD or missing upstream. If origin is missing, continue locally and skip push.
-
If the worktree is dirty, auto-stash tracked and untracked files:
git stash push -u -m "merge-upstream auto-stash $(date +%Y%m%d-%H%M%S)"
git stash list -n 1 --format='%gd'
git status --porcelain
Track the stash ref. If the worktree is still dirty after stashing, stop and ask the user to clean it manually.
-
Detect the upstream target branch:
- If
--base=<branch> is provided, fetch and verify upstream/<branch>.
- Otherwise run
git remote set-head upstream -a, then read refs/remotes/upstream/HEAD.
- If detection fails, ask the user for
--base=<branch>.
-
Fetch enough history for a reliable merge base:
git rev-parse --is-shallow-repository
git fetch --tags upstream "+refs/heads/${upstream_branch}:refs/remotes/upstream/${upstream_branch}"
git fetch origin "+refs/heads/${current_branch}:refs/remotes/origin/${current_branch}"
git merge-base HEAD "upstream/${upstream_branch}"
If the repository is shallow, unshallow origin first when available, then upstream only if still shallow.
-
Report divergence:
git rev-list --count "upstream/${upstream_branch}..HEAD"
git rev-list --count "HEAD..upstream/${upstream_branch}"
GIT_PAGER=cat git log --oneline "HEAD..upstream/${upstream_branch}"
GIT_PAGER=cat git log --first-parent --oneline "upstream/${upstream_branch}..HEAD"
-
Merge:
-
If behind is 0, skip merge.
-
If behind is greater than 0 and --ff-allow is set with ahead 0, run:
git merge --ff-only "upstream/${upstream_branch}"
-
Otherwise capture previous_head and upstream_tip, then run:
git merge --no-ff "upstream/${upstream_branch}" -m "merge: sync ${current_branch} with upstream/${upstream_branch}"
-
Resolve conflicts locally when they occur:
git diff --name-only --diff-filter=U
Read each conflicted file. Auto-resolve only mechanically obvious conflicts such as non-overlapping additions, import unions, formatting-only differences, or generated lockfile refreshes. For semantic conflicts, present the specific conflict and ask whether to keep ours, keep theirs, manually edit, or abort. After resolution:
git add <file>
git -c core.editor=true merge --continue
-
Verify:
git rev-parse --git-path MERGE_HEAD
git rev-parse --git-path rebase-merge
git rev-parse --git-path rebase-apply
git show -s --format=%P HEAD
git rev-list --left-right --count "upstream/${upstream_branch}...HEAD"
git merge-base --is-ancestor "origin/${current_branch}" HEAD
In default mode, verify HEAD has two parents: previous_head as first parent and upstream_tip as second parent. In --ff-allow fast-forward mode, verify HEAD equals upstream_tip.
-
Push only with explicit approval:
GIT_PAGER=cat git log --oneline --graph --decorate -10
git push origin "${current_branch}"
If the remote branch does not exist, use git push -u origin "${current_branch}". If push is rejected as non-fast-forward, re-fetch and offer only non-destructive options: merge origin/<branch> into HEAD and retry, or stop.
-
Restore the stash when one was created:
git stash pop "$stash_ref"
If pop conflicts, leave the stash entry in place and report the exact ref.
Final Report
Include:
- branch and upstream target
- whether merge, fast-forward, or no-op happened
- fork commits preserved
- upstream commits integrated
- push status
- stash status
- any conflicts and how they were resolved
