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CI: what a push queues

The table

Three mechanisms decide what a push does to CI, and they interact:

Dedupe. A job's result is a property of the commit's tree. A commit that already has a passed, queued or running build for a job is not queued again; a commit whose tree already passed a job gets that result as its status, naming the build it came from (#177). A failed, cancelled or abandoned build does not count: that commit runs again.
Path filters. paths and paths-ignore on a job are evaluated against the files the push changed. The diff base is the old tip when it is an ancestor of the new one, and the merge base with the default branch otherwise: a new branch, or a force push after a rebase (#176). A filter that cannot be evaluated, because there is no diff base or the diff fails, runs the job rather than skipping it. A filter that excludes the push records a skipped status, which require-checks accepts (#172).
The reaper. A build a runner claimed and never reported is failed by the scheduler's tick: two minutes after its log stream ended, or at the build deadline if no stream was ever seen (#179). Its status reads build abandoned.

Which runner takes a build is the fourth: a build is claimed only by a runner attached to its repository (or one polling with a full-scope admin key), and an untrusted build only by one started with -untrusted. A repository with no runner attached queues builds nothing claims. See the Users page. Among what a runner may claim it takes the oldest pending build, across every repository it serves; a repository that must never wait on another gets a runner of its own (decided in krz/gitbay#207). There is no cap on how many builds an account queues or how often a schedule fires, and none is planned (krz/gitbay#206): a tick queues nothing while the job's last build is pending or running, so a repository with no runner holds one row per scheduled job, and a schedule with a runner attached spends its owner's compute, not the instance's.

Scheduled jobs run on their cron against the default branch, never on push; a default-branch push registers or updates them. Tag jobs run on a matching tag push and nothing else.

A running build is followed with build log <owner/name> <n> --follow: the stored log, then output as the runner sends it, then the outcome as build <n> <status> on stderr once the build ends. The exit code is 0 whatever the outcome. A follow of a build still queued after ten minutes ends on its own and says so on stderr, since nothing reaps a queued build. The build page does the same without JavaScript while a build is queued or running; ?follow=0 renders it once. An account holds at most eight follows open, and signed-out viewers share one account's eight. Over the JSON API the command answers when the build ends, with the whole log. Read access is checked again every two seconds: a follower who loses it is told the repository is not found. A restart ends every open follow with a message saying so, rather than holding the drain; follow again once the daemon is back.

The table

One ci.yml with five jobs, each isolating one rule:

jobs:
  plain:
    steps: [echo plain]
  onapp:
    paths: [app/**]
    steps: [echo onapp]
  notapp:
    paths-ignore: [app/**]
    steps: [echo notapp]
  nightly:
    schedule: "0 3 * * *"
    steps: [echo nightly]
  release:
    tags: "v*"
    steps: [echo release]

Every push below changes app/x and nothing else, so a push whose filters are evaluated queues onapp and skips notapp, and a push whose filters cannot be evaluated queues both. Each cell is what the push produced for that job; the commit's ci/<job> status follows:

queued: a build, and a pending status until the runner reports. queued, untrusted is a build without the repository's secrets.
skipped: no build, and a skipped status naming the filter.
reused: no build, and a success status naming the earlier build with the same tree.
registered: no build; the job's schedule is (re)registered.
abandoned: the build failed and the status reads build abandoned.
—: nothing new. A status the commit already had stands.

push	plain	onapp	notapp	nightly	release	ci/config
first push of the default branch	queued	queued	queued	registered	—	—
push to the default branch	queued	queued	skipped	registered	—	—
push to another branch	queued	queued	skipped	—	—	—
a new branch, no old sha	queued	queued	skipped	—	—	—
rebase onto a moved default branch, old not an ancestor	queued	queued	skipped	—	—	—
rewritten commit, same tree as a passed build	reused	reused	skipped	—	—	—
fast-forward of a commit built on another branch	—	—	—	registered	—	—
a commit whose earlier build failed, on a new branch	queued	queued	—	—	—	—
merge request head from a fork	queued, untrusted	queued, untrusted	queued, untrusted	—	—	—
tag push	—	—	—	—	queued	—
schedule tick on the default branch	—	—	—	queued	—	—
schedule tick while the last scheduled build is still pending	—	—	—	—	—	—
claimed builds whose runner vanished	abandoned	abandoned	—	—	—	—
push to the default branch with an old sha that cannot be diffed	queued	queued	queued	registered	—	—
push with a broken ci.yml	—	—	—	—	—	failure
push with no ci.yml	—	—	—	—	—	—

Rows worth a second look:

The first push of the default branch has no diff base at all: the merge base of the tip with itself is the tip. Every filtered job runs. The same holds when the old sha cannot be diffed on the default branch; on any other branch the merge base takes over and the filters apply.
A rewritten commit with the same tree reuses plain and onapp because the tree check comes before the filter. notapp never had a passed build to reuse, and the push changed nothing, so the filter skips it again.
A fast-forward of a commit built elsewhere queues nothing: the builds belong to the commit, not the branch. The default-branch push still registers the schedule.
A failed build does not stand for its commit. The same commit pushed to another branch runs again; notapp keeps its skipped status.
A merge request head from a fork has no diff base and, unlike a branch push, no merge-base fallback: every job runs, without secrets. Filtering a head down to no jobs would make it unmergeable under require-checks (#172).

TestPushShapes in internal/hookd runs every row against real git and the store, and TestPushShapesTableOnWiki checks that this page carries each row as the code has it. A row that changes fails there first.