merge-upstream

# 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: ```text /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 bypass hooks or signing with `--no-verify` or `--no-gpg-sign`. - Ask before pushing. ## Workflow 1. Validate the repository: ```bash 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. 2. Require a clean worktree: ```bash worktree_status=$(git status --porcelain) || exit 1 test -z "$worktree_status" ``` If dirty, stop and ask the user to clean or commit the changes, or use a clean task worktree. 3. 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>`. 4. Fetch enough history for a reliable merge base: ```bash git rev-parse --is-shallow-repository git fetch --tags upstream "+refs/heads/${upstream_branch}:refs/remotes/upstream/${upstream_branch}" origin_branch_exists=false if git remote get-url origin >/dev/null 2>&1; then if ! origin_branch=$(git ls-remote --heads origin "refs/heads/${current_branch}"); then echo "failed to inspect origin/${current_branch}" >&2 exit 1 elif [ -n "$origin_branch" ]; then git fetch origin "+refs/heads/${current_branch}:refs/remotes/origin/${current_branch}" || exit 1 origin_branch_exists=true else echo "origin/${current_branch} does not exist; current branch is unpublished" fi fi git merge-base HEAD "upstream/${upstream_branch}" ``` If the repository is shallow, unshallow `origin` first when available, then `upstream` only if still shallow. Always use the fetched remote-tracking ref as the target; do not decide from a previously cached `upstream/<branch>` tip. 5. Record the exact refs and report divergence: ```bash current_head=$(git rev-parse HEAD) upstream_tip=$(git rev-parse "upstream/${upstream_branch}") git rev-list --count "upstream/${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/${upstream_branch}..HEAD" ``` Report `HEAD` and `upstream/${upstream_branch}` with their full SHAs. 6. Merge: - Behind `0` means the fetched `upstream_tip` is already an ancestor of `current_head`. Confirm that state with both checks: ```bash git merge-base --is-ancestor "$upstream_tip" "$current_head" upstream_range=$(git rev-list "$current_head..$upstream_tip") || exit 1 test -z "$upstream_range" ``` This completes upstream integration as a successful no-op. Report the exact refs, SHAs, ancestry result, and empty range; skip the merge, release, and other change-dependent gates. Do not create an empty commit or pull request, or publish a branch solely to represent the sync. If an independent request explicitly approves pushing existing local commits, use step 9's non-destructive push semantics. - If behind is greater than `0` and `--ff-allow` is set with ahead `0`, run: ```bash git merge --ff-only "upstream/${upstream_branch}" ``` - Otherwise capture `previous_head` and `upstream_tip`, then run: ```bash git merge --no-ff "upstream/${upstream_branch}" -m "merge: sync ${current_branch} with upstream/${upstream_branch}" ``` 7. Resolve conflicts locally when they occur: ```bash 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: ```bash git add <file> git -c core.editor=true merge --continue ``` 8. Verify: ```bash 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/${upstream_branch}...HEAD" if [ "$origin_branch_exists" = true ]; then git merge-base --is-ancestor "origin/${current_branch}" HEAD fi ``` In default mode, verify HEAD has two parents: `previous_head` as first parent and `upstream_tip` as second parent. In `--ff-allow` fast-forward mode, verify HEAD equals `upstream_tip`. 9. Push only with explicit approval: ```bash GIT_PAGER=cat git log --oneline --graph --decorate -10 git push origin "${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. ## Final Report Include: - branch and upstream target, including their full SHAs - whether merge, fast-forward, or no-op happened - for a no-op, confirmed ancestry and the empty `HEAD..upstream/<branch>` range - fork commits preserved - upstream commits integrated - push status - any conflicts and how they were resolved