oh-merge

Like drummer, but for GitHub issue PRs (from oh-task) instead of ba task PRs (from mouse). Holistically review pending PRs, then squash-merge them as a cohesive batch.

Invocation

/oh-merge

Flow

Read dive context (if available) for project background:

cat .wm/dive_context.md 2>/dev/null || echo "No dive context"

Find all PRs with oh-merge label:
```
gh pr list --label oh-merge --json number,title,headRefName,baseRefName,additions,deletions
```
Only PRs with the oh-merge label are eligible for merge.

IMPORTANT: PRs with merge conflicts ARE eligible. The skill rebases and resolves conflicts in step 6. Do NOT skip PRs because of conflict status - that's exactly what this skill handles.
Build dependency graph and identify stacks:
- Create adjacency list: baseRefName → [PRs targeting it]
- Find root PRs: those where baseRefName = main (or master)
- Identify stacks: chains where child PRs target parent PR branches
- Detect cycles: If a branch eventually targets itself, report error and skip
- Example graph:
```
main ← PR #42 (issue/123) ← PR #43 (issue/456)
main ← PR #44 (issue/789)  [separate stack]
```
Select stack to process:
- If multiple independent stacks exist, pick first by lowest root PR number (FIFO by age)
- If multiple PRs target the same base branch, order by PR number (lowest first)
- Report other stacks as "queued for next run"
- Process only one stack per invocation to keep merges atomic
- Orphaned children: If a child PR targets a branch that doesn't exist (parent merged externally), update its base to main and treat as a root
Batch review - evaluate all PRs in the selected stack together:
- Collect combined diff of all PRs against main
- Run sg review on the combined changes
- Evaluate:
  - Do changes conflict logically? (same code modified differently)
  - Is there duplicate work? (two PRs solving same problem)
  - Do changes compose well? (feature A + feature B = coherent whole)
  - Any cross-cutting concerns? (shared dependencies, API changes)
- If concerns found:
  - Report issues
  - Ask human whether to proceed or address first
Merge stack in dependency order (root first, then children):

For each PR in the stack, starting from the root:

a. Verify CI is passing:
```
gh pr checks <pr-number> --fail-on-error
```
If CI is failing, stop and report error.

b. Rebase onto its target branch:
```
git fetch origin
gh pr checkout <pr-number>
git rebase origin/<base-branch>  # main for root, parent branch for children
```
c. Resolve any rebase conflicts (this is expected and normal):
- Conflicts WILL occur when main has moved since the PR was created
- Use standard git conflict resolution to fix each conflicting file
- This is the core value of oh-merge - handling what GitHub can't auto-merge
- Only fail if conflicts are truly unresolvable (contradictory changes)
d. Push rebased branch:
```
git push --force-with-lease
```
e. Squash merge:
```
gh pr merge <pr-number> --squash
```
f. For child PRs in the stack (after parent merged):
- Update base branch to main:
```
gh pr edit <child-pr-number> --base main
```
- Rebase child onto main:
```
gh pr checkout <child-pr-number>
git rebase origin/main
git push --force-with-lease
```
- Now child PR targets main and is rebased, continue to merge it (step a-e)
g. On merge failure - If any PR in the stack fails to merge:
- Stop processing the stack
- Report which PRs were merged successfully and which failed
- Signal error: already-merged PRs stay merged, failed PR remains open
- Next oh-merge run will see the failed PR as a new root (its parent is now in main)
Note: Unlike drummer, no ba finish step is needed. GitHub automatically closes linked issues when the PR merges (via "Closes #N" in the PR body).

Stacked PRs

When PRs target other PR branches (not main), oh-merge detects the stack and processes it:

Detection:

gh pr list --label oh-merge --json number,title,headRefName,baseRefName

PRs with baseRefName = main are roots
PRs with baseRefName = issue/<number> are children targeting that parent
Ignore merge conflict status - we handle conflicts during rebase

Graph building:

adjacency[baseRefName] = [list of PRs targeting it]

Example:
  adjacency["main"] = [PR #42, PR #44]
  adjacency["issue/123"] = [PR #43]

Stack 1: main ← #42 (issue/123) ← #43 (issue/456)
Stack 2: main ← #44 (issue/789)

Merge sequence (for Stack 1):

Merge #42 to main
Update #43: gh pr edit 43 --base main
Rebase #43 onto main: git rebase origin/main && git push --force-with-lease
Merge #43 to main

After processing:

Before:  PR #43 → issue/123 → main
         PR #42 → main
         PR #44 → main (separate stack)

After:   PR #42 merged to main (issue #123 auto-closed)
         PR #43 rebased onto main, merged to main (issue #456 auto-closed)
         PR #44 remains for next oh-merge run

Batch Review Criteria

The holistic review checks what individual PR reviews can't:

Logical conflicts: PR A assumes X, PR B assumes not-X
Duplication: Both PRs add similar functionality
Integration issues: Combined changes break something neither breaks alone
Ordering dependencies: PR B depends on PR A being merged first (auto-detected for stacked PRs)
Scope creep: Batch as a whole does more than originally intended

Prerequisites

PRs must have the oh-merge label (human approval gate)
PRs must have CI passing
PRs should have "Closes #N" in body for auto-close (created by oh-task)
Batch review must pass (or human override)

Note: The oh-merge label must be created in the repo. This is opt-in per repo.

Exit Conditions

Success: Selected stack fully merged
Partial success: Some PRs in stack merged, then failure
Needs attention: Batch review raised concerns - waiting for human decision
Error: Unrecoverable failure (code conflicts, CI failing, cycle detected)
No work: No PRs with oh-merge label found

Completion Signaling (MANDATORY)

CRITICAL: You MUST signal completion when done. Call the signal_completion tool as your FINAL action.

Signal based on outcome:

Outcome	Call
Stack merged	`signal_completion(status: "success", message: "Merged N PRs")`
No PRs to merge	`signal_completion(status: "success", message: "No PRs with oh-merge label")`
Partial success	`signal_completion(status: "error", error: "Merged N PRs, failed on PR #X: <reason>")`
Unrecoverable failure	`signal_completion(status: "error", error: "<reason>")`

If you do not signal, the orchestrator will not know you are done and the session becomes orphaned.

Fallback: If the signal_completion tool is not available, output your completion status as your final message in the format: COMPLETION: status=<status> message=<message> or COMPLETION: status=<status> error=<reason>.

Example

Basic (no stacks)

$ /oh-merge

Finding PRs with oh-merge label...
Found 2 PRs:
  PR #42 "Fix validation bug" (issue/123) → main (CI ✓)
  PR #44 "Refactor validator" (issue/789) → main (CI ✓)

Building dependency graph...
  Stack 1: main ← #42
  Stack 2: main ← #44
  2 independent stacks, processing Stack 1

Running batch review on Stack 1 (1 PR)...
Batch review complete: ✓ No issues

Processing PR #42 (Fix validation bug)...
  Verifying CI... ✓
  Rebasing onto main... clean
  Squash merging... ✓
  Issue #123 will auto-close on merge

Merge complete.
  Merged: 1 PR (#42)
  Remaining: 1 PR (#44 - queued for next run)

signal_completion(status: "success", message: "Merged 1 PR (#42)")
Done.

Stacked PRs

$ /oh-merge

Finding PRs with oh-merge label...
Found 3 PRs:
  PR #42 "Fix validation bug" (issue/123) → main (CI ✓)
  PR #43 "Add edge case tests" (issue/456) → issue/123 (CI ✓)
  PR #44 "Refactor validator" (issue/789) → main (CI ✓)

Building dependency graph...
  Stack 1: main ← #42 (issue/123) ← #43 (issue/456)
  Stack 2: main ← #44
  2 stacks found, processing Stack 1 (2 PRs)

Running batch review on Stack 1...
Collecting diffs: +547 -103 across 8 files
Batch review complete: ✓ No issues

Processing stack root: PR #42 (Fix validation bug)...
  Verifying CI... ✓
  Rebasing onto main... clean
  Squash merging... ✓
  Issue #123 will auto-close on merge

Processing stack child: PR #43 (Add edge case tests)...
  Verifying CI... ✓
  Updating base branch to main... done
  Rebasing onto main... clean
  Squash merging... ✓
  Issue #456 will auto-close on merge

Stack merged.
  Merged: 2 PRs (#42, #43)
  Remaining: 1 PR (#44 - queued for next run)

signal_completion(status: "success", message: "Merged 2 PRs (#42, #43)")
Done.