gh-stack

# gh-stack

`gh stack` is a [GitHub CLI](https://cli.github.com/) extension for stacked branches and pull
requests. A stack is an ordered chain of branches rooted on a trunk, where each branch has one PR
based on the branch below it, so a reviewer sees only that layer's diff.

`gh stack` prints a stack trunk-first, left to right:

```
(main) <- auth <- api <- frontend
```

Left is the **bottom**, right is the **top**. `auth` is based on `main` and merges first;
`frontend` merges last. `up` moves toward the top, away from trunk; `down` moves toward it.
Foundational work belongs at the bottom, code that depends on it above. For how to choose the
layers, read `references/stack-design.md`.

## Setup

```bash
gh extension install github/gh-stack
git config rerere.enabled true         # remember conflict resolutions
git config remote.pushDefault origin   # required if the repo has more than one remote
```

## Non-interactive use

`gh stack` branches on whether **stdout is a TTY**. Piped, most commands error cleanly or print
static text; under a PTY the same commands open a prompt or a full-screen TUI and block forever.
Agent harnesses differ, so always pass the flags below instead of relying on that detection.

**Multiple remotes:** never run `push`, `submit`, `sync`, `rebase`, or `link` without
`--remote <name>` unless `remote.pushDefault` is configured. `checkout` and `trunk` have no
`--remote` flag and require the config.

| Always run | Never run bare | Why |
|---|---|---|
| `gh stack view --json` | `gh stack view` | opens a TUI under a PTY |
| `gh stack submit --auto` | `gh stack submit` | prompts for a title per new PR |
| `gh stack merge <target> --yes` | `gh pr merge` | `gh pr merge` cannot merge a stack |
| `gh stack init <branch>...` | `gh stack init` | prompts for branch names |
| `gh stack add <branch>` | `gh stack add` | prompts for a name, and fails even when piped |
| `gh stack checkout <target>` | `gh stack checkout` | opens a selection menu |
| `gh stack up` / `down` / `top` / `bottom` | `gh stack switch` | `switch` is menu-only |
| — | `gh stack modify` | TUI-only, no non-interactive path |

- `view --short` is safe in both modes, but it is formatted for humans. Use `--json` to parse.
- **`checkout <pr>` when a different local stack already covers those branches** cannot be forced.
  Run `gh stack unstack --local` first (this keeps the stack on GitHub), then retry.

## Branch placement

- **Starting multi-part work:** create the stack before writing files. Do not implement every
  concern on trunk and split it later. Put one dependent concern in each layer, bottom to top.
- **Editing an existing stack:** check out the layer that owns the change before editing. Never
  commit a lower layer's concern on the current top branch. Run `gh stack view --json`; if
  ownership is unclear, inspect `git log --all -- <path>`. Then check out the owner, edit, commit,
  rebase upstack, and return to top.

```bash
gh stack down                   # or: gh stack checkout api
git add ... && git commit -m "Add get-user endpoint"
gh stack rebase --upstack       # replay every branch above onto the change
gh stack top                    # return to where you were
gh stack push
```

## Core loop

```bash
gh stack init auth              # create the stack and check out its branch
git add ... && git commit -m "Add auth middleware"
gh stack add api                # next layer, branched from the current one
git add ... && git commit -m "Add API routes"
gh stack submit --auto          # push every branch and open draft PRs
gh stack view --json            # confirm
```

Add `--open` to `submit` to create PRs ready for review instead of drafts. Branch names are
verbatim — `gh stack add refactor/foo` creates `refactor/foo`.

## Staying in sync

```bash
gh stack sync                   # fetch, reconcile with GitHub, rebase, push, refresh PR state
gh stack sync --prune           # also delete local branches for merged PRs
```

Pruning never happens without `--prune` when non-interactive. If the local and remote stacks have
diverged, `sync` prints both chains, makes no changes, and exits 0 with `Sync aborted` — see
`references/troubleshooting.md`.

## Merging

Scope the merge with an argument:

```bash
gh stack merge 42 --yes          # PR #42 plus every unmerged PR below it
gh stack merge 7 --yes           # every unmerged PR in stack #7
gh stack merge 42 --yes --squash # or --merge, --rebase, --merge-method <method>
```

Pass a PR number to merge that PR and every unmerged PR below it, or a stack number to merge every
unmerged PR in that stack. The operation is all-or-nothing: if any PR in that set cannot merge,
none do.

Without a method flag the last-used method is reused. If the base branch uses a merge queue, the
stack is queued instead and the queue picks the method, ignoring any flag you passed with a
warning; queued PRs may land in separate groups.

## Reading state

`gh stack view --json` writes JSON to **stdout**. Status messages go to **stderr** — do not parse
them, branch on exit codes instead.

```
trunk           string
currentBranch   string
branches[]      name, head, base, isCurrent, isMerged, isQueued, needsRebase
branches[].pr   number, url, state ("OPEN" | "MERGED" | "QUEUED"); absent when no PR exists
```

`base` is the saved SHA of the parent branch that this branch was last known to contain. It may be
older than the parent's current tip. `needsRebase` is true when the current parent tip is no longer
an ancestor of the branch.

## Exit codes

| Code | Meaning | Recovery |
|---|---|---|
| 0 | Success | — |
| 1 | Generic error | Read stderr |
| 2 | Not in a stack | `gh stack init`, or `gh stack checkout <target>` |
| 3 | Rebase conflict | Follow the Exit 3 recovery below |
| 4 | GitHub API failure | Check `gh auth status`, retry |
| 5 | Invalid arguments | Fix the invocation; see `<command> --help` |
| 6 | Disambiguation required | Branch is in several stacks; check out a non-shared branc