name: coverage

# Manual dispatch ONLY — deliberately not on `pull_request`, and
# deliberately not nightly.
#
# A coverage run needs its own instrumented build: it cannot reuse the
# normal test artifacts, so it roughly doubles a test job. Coverage here
# answers "do we have glaring holes", which is a question someone asks
# occasionally — not a gate every PR pays for, and not a number worth
# spending farm time on every night whether or not anyone reads it.
# Manual dispatch costs nothing until someone wants the answer.
#
# Its own file rather than a job in ci.yml: that workflow already has a
# `workflow_dispatch` trigger (so `hive-forge ci-rerun` can retrigger
# without an empty commit), and a trigger there fires EVERY job in the
# file. A coverage job added to ci.yml would run on every pull request.
on:
  workflow_dispatch:

jobs:
  coverage:
    name: cargo llvm-cov
    runs-on: [hive-ci]
    # Above the 30 min `nix flake check` allows, because instrumented
    # builds are slower than the ordinary ones and this starts from a
    # cache that the normal jobs never populate.
    timeout-minutes: 60
    steps:
      - uses: actions/checkout@v3
      - name: coverage
        # No threshold and no `--fail-under-lines`: a coverage gate
        # mostly teaches people to write assertion-free tests that
        # execute lines. The report is the deliverable; the number is
        # for a human to look at.
        #
        # `--workspace` because the interesting holes are in the crates
        # nobody runs directly, and the per-crate default would hide
        # exactly those behind a green summary for the one crate someone
        # happened to name.
        run: nix develop -c cargo llvm-cov --workspace --summary-only