name: CI

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]
    # Spelled out only to keep `ready_for_review` in the list — naming any type
    # replaces the whole default set, so the other three have to be restated.
    # It is inert on this instance (draft state here is the `WIP:` title
    # prefix, so un-drafting is a title edit and raises no
    # `ready_for_review` action) and costs nothing.
    #
    # The consequence, which is the part that bites: the `if:` guard below is
    # evaluated when a run is CREATED, and un-drafting creates no run. A PR
    # opened as a draft keeps its skip decision until something else produces
    # one. Push an empty commit after un-WIP'ing.
    types: [opened, synchronize, reopened, ready_for_review]

# gitdan-ci runs four repos' CI on two capacity slots, and the compiler-backed
# suites below are multi-minute. A superseded run costs a slot in front of
# somebody's build, so drop it.
#
# `push` groups on `github.sha` rather than `github.ref`: a constant per-branch
# group is what let this Gitea (1.26.0) cancel two of daniel/gitdan's merge
# runs outright while `cancel-in-progress` was gated away from `push` entirely
# — see the long note in that repo's ci.yaml for the evidence. Giving every
# commit its own group leaves that behaviour nothing to act on.
concurrency:
  group: ${{ github.workflow }}-${{ github.event_name == 'pull_request' && github.ref || github.sha }}
  cancel-in-progress: true

jobs:
  selftest:
    name: shellcheck + selftests
    # Two clauses, both load-bearing. The second skips draft PRs: Gitea sets
    # draft:true when the title starts with `WIP:`, so work-in-progress pushes
    # cost the shared runner nothing until the PR is un-WIP'd. The first is
    # what keeps that from also skipping pushes to `main` — a `push` event has
    # no `pull_request` context, so `github.event.pull_request.draft` is empty
    # there and the negation alone would be unreliable. Never drop it.
    if: ${{ github.event_name != 'pull_request' || !github.event.pull_request.draft }}
    runs-on: ubuntu-latest
    timeout-minutes: 20
    # Deliberately no `container.volumes:` entry, unlike every repo that
    # CONSUMES this action. The suites below build throwaway workspaces under
    # `mktemp -d` and want a cold target dir every time — a persistent cache
    # would make "did this run rebuild?" unanswerable, which is the question
    # restore-mtimes-selftest.sh exists to ask. So this job takes no share of
    # the shared CI cache disk budget.
    steps:
      - name: Checkout sources
        uses: actions/checkout@v4

      - name: Install shellcheck
        uses: taiki-e/install-action@v2
        with:
          tool: shellcheck

      # `hardlink-clone-selftest.sh` and `restore-mtimes-selftest.sh` drive a
      # real Cargo against a real scratch workspace — they are the only things
      # here that verify the hardlink-aliasing and mtime-freshness behaviour
      # against the compiler rather than against a fixture, and selftest.sh's
      # own header says `--fast` is for iterating, not for signing off a
      # change. So CI installs a toolchain and runs the full set.
      #
      # The scratch workspaces use path dependencies only, so nothing here
      # reaches crates.io.
      # Nightly first, stable second, so stable ends up the default and
      # nightly is only reachable through an explicit `+nightly`.
      #
      # `hardlink-clone-selftest.sh`'s last scenario needs a Cargo that
      # resolves freshness by CONTENT — the mode where the dep-info file
      # carries per-source checksums, which is the mutation that turns a
      # hardlink clone into silent stale-artifact reuse rather than a slow
      # build. This step is what supplies it, and as of 2026-08-26 it does:
      # the scenario ran and passed against 1.100.0-nightly.
      #
      # It briefly did not. Cargo PR #17382 (2026-08-22) demoted
      # `-Z checksum-freshness` to a gate and gave `build.fingerprint` the
      # choice, defaulting to `mtime`, so the suite — which set only the gate —
      # measured a genuine INACTIVE and skipped its strongest scenario. That
      # read as "upstream withdrew content freshness" and was written up here
      # as this step buying nothing. It was a moved switch, not a withdrawal;
      # the suite now exports both and the coverage is back. See
      # daniel/gitdan#62 for the investigation.
      - name: Install Rust nightly
        uses: dtolnay/rust-toolchain@nightly
      - name: Install Rust toolchain
        uses: dtolnay/rust-toolchain@stable

      # Every script, including the suites themselves. `-x` follows the
      # `. cache-lib.sh` each one sources, which is where most of the logic
      # being checked actually lives; without it shellcheck reports SC1091 and
      # analyses each file with a hole in it.
      - name: shellcheck
        run: shellcheck -x --source-path=scripts scripts/*.sh

      # One command, not six: selftest.sh is the entry point a developer runs,
      # so a suite added there is gated here without a matching edit in this
      # file.
      - name: Selftests
        run: bash scripts/selftest.sh