name: CI

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]
    # Spelled out only to keep `edited` in the list — naming any type replaces
    # the whole default set, so the other three have to be restated.
    #
    # `edited`, not `ready_for_review`: draft here is the `WIP:` title prefix,
    # so un-drafting is a title edit and no ready-for-review action is ever
    # raised. That edit is what creates the run which lifts the `if:` skip
    # below (decided once, when a run is CREATED). Do not swap it back and do
    # not drop this to the bare default — either restores the bug. The accepted
    # cost and the evidence are in README's Development section.
    types: [opened, synchronize, reopened, edited]

# 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 A superseded run costs a slot in front of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 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. Observed on 1.26.0; the instance
# is 1.27.2 now and whether it persists is unverified, which is why every
# commit gets its own group instead of trusting the flag.
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

  release-tag:
    name: move v1 to main
    # `needs:` is what makes this "after the gate is green" rather than
    # merely "after a push": a failed selftest skips this job outright, so
    # v1 can never advance onto a broken build. The `if:` restricts it to an
    # actual push to main -- a pull_request run targeting main shares this
    # workflow but has no ref worth tagging.
    needs: selftest
    if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/main' }}
    runs-on: ubuntu-latest
    timeout-minutes: 2
    # The workflow-level group above is keyed per-commit (github.sha) so
    # unrelated commits' CI never blocks each other -- which also means two
    # merges landing close together can run two concurrent release-tag jobs.
    # A job-level `concurrency:` is a second, independent group scoped to
    # this job alone -- it does not replace the workflow-level one, it adds
    # to it (confirmed by reading gitea's source at the v1.27.2 tag this
    # instance runs: run-level and job-level concurrency are separate model
    # fields, evaluated and enforced by separate functions --
    # CancelPreviousJobsByRunConcurrency vs CancelPreviousJobsByJobConcurrency
    # in models/actions/{run,run_job}.go -- not one overriding the other).
    # This serialises jobs that are actually running or queued AT THE SAME
    # TIME -- it has no notion of commit order between jobs that never
    # overlap. Two release-tag runs on a 2-slot, 4-repo runner with a
    # multi-minute selftest ahead of each can easily not overlap at all,
    # finishing in either order regardless of push order. The step below is
    # what makes the OUTCOME order-independent; this group only bounds how
    # much work is wasted getting there.
    concurrency:
      group: release-tag-v1
      cancel-in-progress: false
    # Requests write access from the run's built-in token (see README's
    # Versioning section for what's actually verified about it). Without
    # this the checkout below still succeeds -- it's the push that would be
    # rejected, which is a red job, not a silent no-op.
    permissions:
      contents: write
    steps:
      # fetch-depth: 0 fetches full history AND all tags (actions/checkout's
      # own description: "0 indicates all history for all branches and
      # tags") -- REQUIRED so refs/tags/v1 and the ancestry behind it are
      # both present locally for the merge-base check below, regardless of
      # which commit this run happens to be built from.
      - uses: actions/checkout@v4
        with:
          token: ${{ secrets.GITHUB_TOKEN }}
          fetch-depth: 0

      # The concurrency group above only excludes a SIMULTANEOUS competing
      # push; it does nothing for two release-tag jobs that never overlap
      # and finish in the opposite order from the merges that triggered
      # them -- which a shared 2-slot runner and a multi-minute selftest
      # ahead of this job make routine, not rare. So the push itself has to
      # be safe regardless of completion order: skip whenever v1 already
      # points at this commit or a descendant of it, rather than trusting
      # this run to be the last one to finish. `--is-ancestor` treats a
      # commit as its own ancestor, so "already at" and "already ahead" are
      # one case. A v1 that doesn't exist yet, or that shares no history
      # with this commit, falls through to the push below -- the guard is
      # only ever a reason to skip, never a reason to fail.
      - name: Skip if v1 already at or ahead of this commit
        id: check
        run: |
          if git rev-parse -q --verify refs/tags/v1 >/dev/null \
             && git merge-base --is-ancestor "${{ github.sha }}" refs/tags/v1; then
            echo "v1 already at or ahead of ${{ github.sha }} -- nothing to do"
            echo "skip=true" >> "$GITHUB_OUTPUT"
          else
            echo "skip=false" >> "$GITHUB_OUTPUT"
          fi

      # Lightweight tag, matching what v1 already is (`git cat-file -t v1`
      # reports `commit`, not `tag`) -- no identity needed to move it, only
      # to push it.
      - name: Force v1 to this commit
        if: steps.check.outputs.skip != 'true'
        run: |
          git tag -f v1 "${{ github.sha }}"
          git push --force origin v1