/external-pr-ci-trigger

Mirror an external contributor's fork branch onto DataDog/saluki as <owner>/<branch> so CI runs against the contributor's PR. The contributor's PR keeps its check status updated by GitHub because the head commit of the mirrored branch matches the PR's head commit.

This skill performs destructive-ish local-git operations (adding a remote, creating a branch, pushing to origin). Read the steps carefully, validate preconditions, and stop on the first failure with the printed recovery commands.

Argument

A single positional argument in one of two forms:

Form A — PR number (preferred): an all-digits string like 1234. The skill resolves the contributor's owner, branch, and fork repo name from the PR via gh. See Step 0.

Form B — explicit owner/branch: <owner>:<branch>, for cases where you don't have a PR number handy (for example, you want to mirror a branch that doesn't have a PR yet).

• <owner> matches [a-zA-Z0-9_-]+
• <branch> matches [a-zA-Z0-9.#_/-]+ (dots are allowed for branches like release/1.2.3)
• The whole string MUST NOT contain a single quote (').

Examples: 1234, octocat:fix-thing, octocat:feature/cool-thing, octocat:user#123/wip.

Detection: if the argument is purely digits, treat it as Form A. Otherwise it must contain a :; split once on the first : into OWNER and BRANCH (Form B). If neither shape matches, or it contains a ', stop and ask the user to re-supply it.

The pushed branch on origin will be named OWNER/BRANCH (with a / separator) in both forms.

Step 0: Resolve PR (Form A only — skip if Form B)

For a PR-number argument, fetch the PR's head ref in one call:

gh pr view <PR-NUMBER> --repo DataDog/saluki \
  --json headRefName,headRepositoryOwner,headRepository,isCrossRepository

From the JSON:

• isCrossRepository MUST be true. If false, the PR's branch already lives on

DataDog/saluki and CI is running normally — abort and tell the user this skill isn't needed.

• headRepositoryOwner.login → OWNER
• headRefName → BRANCH
• headRepository.name → FORK_NAME (used in Step 4a; this lets you skip Step 2 entirely for

Form A)

If gh pr view fails (PR doesn't exist, no access, etc.), surface the error and stop.

Validate the resolved OWNER and BRANCH against the same character-class rules from the Argument section — a malicious or unexpected PR head ref shouldn't be allowed to inject shell metacharacters. If either fails validation, abort.

Step 1: Preconditions

Run each check. If any fails, stop immediately and tell the user what's wrong — do not attempt to "fix" their working tree.

# 1a. Working tree must be clean. Any output here aborts.
git status --porcelain

# 1b. The target local branch must not already exist.
git branch --list "OWNER/BRANCH"

# 1c. A remote named OWNER must not already exist.
git remote | grep -Fx "OWNER" || true

# 1d. Capture the current branch so we can restore it at the end.
git branch --show-current

# 1e. origin MUST point at DataDog/saluki. A clone where origin is a personal fork would
#     silently push to the wrong repo and the contributor's PR check status would never
#     update. Accept either SSH or HTTPS form, with or without a trailing `.git`.
git remote get-url origin | grep -Ex '(git@github\.com:|https://github\.com/)DataDog/saluki(\.git)?' || true

For 1a: any non-empty output means the working tree is dirty — abort and ask the user to commit or stash first.

For 1b and 1c: any non-empty output means a stale leftover exists from a prior run. Show the user the recovery commands below and ask them to clean up before retrying.

Save the output of 1d as CURR_BRANCH for use in Step 5.

For 1e: empty grep output (no match) means origin is not DataDog/saluki — abort and tell the user. Do not attempt to "fix" their remotes.

Step 2: Discover the fork's repository name (Form B only — skip if Form A)

For Form A, FORK_NAME was resolved in Step 0; skip this step entirely.

For Form B, the contributor's fork is usually named saluki, but GitHub allows fork renames. Resolve the real name via the GitHub API.

# Fast path: assume the fork is named "saluki" and verify its parent is DataDog/saluki.
gh repo view "OWNER/saluki" --json parent --jq '.parent.nameWithOwner' 2>/dev/null

If that prints DataDog/saluki, set FORK_NAME=saluki and continue.

Otherwise, search the user's forks via GraphQL:

gh api graphql -f query='
  query($login: String!) {
    user(login: $login) {
      repositories(isFork: true, first: 100, ownerAffiliations: OWNER) {
        nodes { name parent { nameWithOwner } }
      }
    }
  }' -F login=OWNER \
  --jq '.data.user.repositories.nodes[] | select(.parent.nameWithOwner == "DataDog/saluki") | .name'

If exactly one name is returned, use it as FORK_NAME. If zero are returned, abort and tell the user the owner has no fork of DataDog/saluki. If more than one is returned (rare — usually means a fork-of-a-fork situation), show the list and ask the user which one to use.

Step 3: Recovery commands (print these now)

Before running anything destructive, surface the cleanup commands so the user can copy them if something goes wrong mid-flow:

git remote remove 'OWNER'
git checkout 'CURR_BRANCH'
git branch -d 'OWNER/BRANCH'

If any command in Step 4 fails, print these and stop. Do not try to continue past a failure or auto-retry — the user needs to inspect state.

Step 4: Fetch, branch, push

Run sequentially. If any command exits non-zero, stop and print the recovery commands.

# 4a. Add the contributor's fork as a remote.
git remote add OWNER [email protected]:OWNER/FORK_NAME.git

# 4b. Fetch only the branch we care about.
git fetch 'OWNER' 'BRANCH'

# 4c. Detached checkout of the fetched commit, then create a local branch from it.
#     The two-step is intentional: the first checkout uses the remote ref and leaves HEAD
#     detached; the second creates the named branch at that commit.
git checkout 'OWNER/BRANCH'
git checkout -b 'OWNER/BRANCH'

# 4d. Push to origin (DataDog/saluki), setting upstream.
git push --set-upstream origin 'OWNER/BRANCH'

If the user passes --no-verify as an extra argument, append --no-verify to the push only. Otherwise do not skip hooks.

Step 5: Restore local state

These run unconditionally after a successful push (and are also the recovery commands from Step 3).

git remote remove 'OWNER'
git checkout 'CURR_BRANCH'
git branch -d 'OWNER/BRANCH'

The local OWNER/BRANCH is safe to delete because we just pushed it; origin/OWNER/BRANCH is the source of truth from here on.

Anti-patterns

• Don't git reset --hard or git clean to "make the working tree clean." If preconditions

fail, surface the failure — the user's uncommitted work is theirs to handle.

• Don't retry on failure. A failed git fetch or git push usually means the branch

doesn't exist on the fork, or the user lacks push access to DataDog/saluki. Surface the error.

• Don't push to anywhere other than origin. This skill assumes origin is

DataDog/saluki. If git remote get-url origin returns something else, abort.

• Don't run on a dirty tree even if "it looks safe." The branch-switching in Step 4 will

carry uncommitted changes into the contributor's branch and may corrupt the push.