mutation-affected.yml

name: Mutation Affected

# PR-side half of the decision-kernel mutation lane (issue #1415).
#
# Advisory only — the lane reports and never gates (#1457). `scripts/mutation/run.ts`
# exits non-zero on a harness failure, never on a score.
#
# Cost control: the kernel report that pays is the weekly sweep, so this lane
# spends mutants on one thing only — proving the harness still runs end to end
# when the harness itself changes. `select` therefore returns an empty matrix
# unless the diff touches the lane's own sources. Selecting on derived kernel
# ownership instead would run the full ten-shard sweep on 24 of the last 40
# merged PRs.
#
# On a harness diff the matrix is the canary (`LANE_CANARY`, selected by
# observed end-to-end runtime within the job budget — lane sources own no kernel,
# so derivation alone would select nothing) plus any kernel that same diff
# reaches through the import graph (scripts/mutation/ownership.ts): a kernel
# source, or a test that reaches one. Selected modules are sharded like the
# weekly sweep, so the PR's wall clock is one module rather than their sum.

on:
  pull_request:
    paths:
      # Exactly `LANE_TOOLING` in scripts/mutation/run.ts plus this file — the
      # only diffs that can produce a non-empty matrix, asserted both ways by
      # scripts/mutation/workflow.test.ts. A kernel or test path here would only
      # start a job that selects nothing.
      - 'scripts/mutation/**'
      - 'scripts/lib/**'
      - 'stryker.config.json'
      - '.github/workflows/mutation-affected.yml'

permissions:
  contents: read

concurrency:
  group: ci-${{ github.workflow }}-${{ github.ref }}
  cancel-in-progress: true

jobs:
  select:
    name: Select affected kernels
    runs-on: ubuntu-latest
    timeout-minutes: 10
    outputs:
      modules: ${{ steps.select.outputs.result }}
    steps:
      - name: Checkout
        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
        with:
          fetch-depth: 0

      - name: Setup toolchain
        uses: ./.github/actions/setup-node-pnpm

      - name: Harness self-test
        uses: ./.github/actions/run-gate
        with: { gate: mutation-model }

      - id: select
        name: Derive the affected shard matrix
        uses: ./.github/actions/run-gate
        with:
          gate: mutation-affected
          args: |
            --list-affected
            --base
            origin/${{ github.event.pull_request.base.ref }}

      # The self-test and the derivation run before any mutant, so a failure here
      # would leave the lane with no envelope at all (#1430).
      - name: Record a failed lane envelope
        if: failure()
        run: |
          pnpm gate mutation --affected --fail-envelope \
            "affected selection failed before any mutant ran (run ${{ github.run_id }})" || true

      - name: Upload selection envelope
        if: failure()
        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
        with:
          name: mutation-affected-select
          include-hidden-files: true
          path: .tmp/mutation/lane-envelope.json
          if-no-files-found: warn

  mutants:
    name: Mutants (${{ matrix.name }})
    needs: select
    if: needs.select.outputs.modules != '[]'
    runs-on: ubuntu-latest
    timeout-minutes: 30
    strategy:
      fail-fast: false
      matrix:
        include: ${{ fromJSON(needs.select.outputs.modules) }}
    steps:
      - name: Checkout
        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2

      - name: Setup toolchain
        uses: ./.github/actions/setup-node-pnpm

      - name: Run mutants for ${{ matrix.name }}
        uses: ./.github/actions/run-gate
        with:
          gate: mutation
          args: |
            --modules
            ${{ matrix.module }}
            ${{ matrix.shard && '--shard' || '' }}
            ${{ matrix.shard || '' }}

      - name: Record a failed shard envelope
        if: failure()
        run: |
          pnpm gate mutation --affected --modules ${{ matrix.module }} --fail-envelope \
            "shard ${{ matrix.name }} failed before producing a report (run ${{ github.run_id }})" || true

      - name: Upload shard report
        if: always()
        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
        with:
          name: mutation-affected-shard-${{ matrix.name }}
          include-hidden-files: true
          path: |
            .tmp/mutation/mutation.json
            .tmp/mutation/mutation.html
            .tmp/mutation/lane-envelope.json
          if-no-files-found: warn

  report:
    name: Affected decision-kernel mutants
    needs: [select, mutants]
    if: always() && needs.select.result == 'success'
    runs-on: ubuntu-latest
    timeout-minutes: 15
    steps:
      - name: Checkout
        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
        with:
          fetch-depth: 0

      - name: Setup toolchain
        uses: ./.github/actions/setup-node-pnpm

      - name: Download shard reports
        if: needs.select.outputs.modules != '[]'
        uses: actions/download-artifact@d3f86a106a0bac45b974a628896c90dbdf5c8093 # v4.3.0
        with:
          pattern: mutation-affected-shard-*
          path: .tmp/mutation/shards

      # No shards means no affected kernel: run.ts reports "nothing to mutate"
      # and still writes the envelope, so the lane is never silently absent.
      # Either invocation writes the score table to $GITHUB_STEP_SUMMARY.
      - name: Score the affected modules
        run: |
          if [ -d .tmp/mutation/shards ]; then
            expected=$(echo '${{ needs.select.outputs.modules }}' | jq length)
            pnpm gate mutation-check --report-dir .tmp/mutation/shards --affected \
              --expect-shards "$expected" \
              --base "origin/${{ github.event.pull_request.base.ref }}"
          else
            pnpm gate mutation-affected --base "origin/${{ github.event.pull_request.base.ref }}"
          fi

      - name: Record a failed lane envelope
        if: failure()
        run: |
          pnpm gate mutation --affected --fail-envelope \
            "affected report failed before producing a score table (run ${{ github.run_id }})" || true

      - name: Upload mutation report
        if: always()
        uses: actions/upload-artifact@ea165f8d65b6e75b540449e92b4886f43607fa02 # v4.6.2
        with:
          name: mutation-affected
          include-hidden-files: true
          path: |
            .tmp/mutation/shards
            .tmp/mutation/lane-envelope.json
          if-no-files-found: ignore