rebase-downstream

Rebase Downstream Tree

Rebase a tree of dependent branches after upstream changes have been made. Auto-detects the downstream branch tree (including sibling branches), rebases each branch in order, resolves conflicts when possible, and runs preflight checks on each branch.

Current State

Branch: !git branch --show-current
Status: !git status --short

Steps

1. Detect current branch

Get the current branch name. This is the branch that was just modified and whose changes need to propagate downstream.

git branch --show-current

2. Auto-detect downstream chain

Run the detect-chain.sh helper script to find all downstream branches:

bash .claude/skills/rebase-downstream/detect-chain.sh <current-branch>

The script outputs branch:parent per line in rebase order (depth-first pre-order). This handles both linear chains and trees with sibling branches.

3. Confirm the chain

Display the detected chain to the user and ask for confirmation before proceeding.

If no downstream branches are detected, report this to the user and stop.

If branches are detected, show the tree visually:

<current-branch>
  → <child1>
    → <grandchild1>
  → <child2> (sibling)

Ask the user to confirm before rebasing. If the user declines, stop.

4. Rebase each branch in order

For each downstream branch (closest to the current branch first):

Checkout the branch:
```
git checkout <downstream-branch>
```
Rebase onto its parent (from the branch:parent output):
```
git rebase --fork-point <parent-branch>
```
--fork-point uses the parent branch's reflog to find the actual fork point, so only the branch's own commits are replayed. Without it, if the parent was rebased/amended, git replays already-applied parent commits with different SHAs, causing duplicate commits and false conflicts.

The parent for each branch is provided by the detect script. For sibling branches, both share the same parent.
Handle conflicts (if any):
- Inspect each conflicted file to understand both sides
- Attempt to resolve the conflict intelligently
- After resolving, stage the files and continue:
```
git add <resolved-files>
git rebase --continue
```
- If a conflict cannot be resolved, abort and stop:
```
git rebase --abort
```
  Report which branch and files had unresolvable conflicts, then stop entirely. Do NOT continue to the next branch.
Run full preflight checks using /preflight on this branch. This includes format, gn_check, presubmit, build, and tests. If preflight fails, stop and report. Do NOT continue to the next branch.
Move to the next branch only after successful rebase and preflight.

5. Return to the original branch

After all branches are rebased successfully, checkout the original starting branch:

git checkout <original-branch>

6. Report results

Summarize the results:

Rebased branches: List each branch that was successfully rebased
Conflicts resolved: Note any conflicts that were auto-resolved and how
Preflight results: Summary of preflight status for each branch
Tree: Show the full rebased tree structure

Important

NEVER skip preflight checks on any branch in the chain
Stop immediately if a rebase conflict cannot be resolved
Stop immediately if preflight fails on any branch
Always return to the original branch at the end (even on failure)
Do not force-push any branches — the user will decide when to push