Pull request previews

Tick Pull request previews on a git service's Source tab and every pull request opened on its repo gets a service of its own, <slug>-pr-<number> (so <slug>-pr-<number>.<baseDomain>), built from the pull request's head and deployed as the service's owner. Each push to the pull request redeploys the preview; closing or merging it deletes the preview, container, DNS records and all. GitHub, Gitea and GitLab previews build the exact head commit; Bitbucket only sends an abbreviated hash, so its previews build the head branch, which covers every pull request previews are made for anyway.

Pull requests from forks are never previewed. On a public repo anyone can open one, and a preview builds and runs its code with the service's env vars. Homerun only previews a pull request whose head is positively the same repository as its base (GitHub and Gitea compare the head and base repository, GitLab the source and target project, Bitbucket the source and destination repository); a fork, or a payload that doesn't say, is acknowledged and ignored.

A preview copies the service's build settings, env vars, resources, stack and login wall when it's created and again on every update, but not its volumes, domains, cron schedule or status checks. Previews are listed under the toggle, and each is a normal service you can open, redeploy or delete (a push to its pull request brings it back). Turning previews off, or deleting the service, deletes every preview.

Previews ride on the same webhook as deploy on push: turning them on re-registers the webhook to also send pull request events. A webhook added by hand needs Pull requests (GitHub, Gitea), Merge request events (GitLab) or the Pull request created, updated, merged and declined triggers (Bitbucket) ticked too. Polling doesn't cover pull requests.