liveness_primer

liveness_primer is a differential testing harness for Python dead-code detectors and static linters. It runs two revisions of a detector against the same pinned open-source projects and reports the blast radius: which findings appeared, disappeared, changed, or could not be produced at all.

Open the static report explorer.

Why use it?

A detector's own test suite can prove that selected examples behave correctly. It is much harder to see how a change affects real projects outside that suite. liveness_primer makes that impact reviewable before a release or merge.

Use it to:

• validate that an internal refactor preserves the detector's findings;
• assess whether a new analysis finds the intended cases without producing a wave of unrelated false positives;
• verify that a bug fix removes or adds the expected findings without creating new false negatives elsewhere;
• catch parser, packaging, dependency, timeout, and execution failures that only appear on some projects;
• compare releases and review changes to locations, messages, confidence, or rule attribution;
• publish a human-readable PR summary and a complete machine-readable report from CI; and
• feed the JSON report into deterministic automation or LLM-assisted triage.

The comparison uses byte-identical, commit-pinned target projects for both detector revisions. Managed runs resolve the requested detector refs, prepare separate fingerprint-keyed environments, run the same configured targets, and normalize detector-specific output into one deterministic report model.

Installation

liveness_primer requires Python 3.12 or newer.

pip install liveness_primer

The built-in adapters support Vulture and Skylos.

License verification (corpus license-check) requires the [license] extra.

Quick start

Compare two Vulture refs on the pinned pluggy corpus project:

liveness-primer run --tool vulture \
  --repo https://github.com/jendrikseipp/vulture \
  --old v2.15 \
  --new v2.16 \
  -k pluggy \
  --output text

Project selection is explicit:

• -k NAME selects matching projects from the packaged, commit-pinned corpus;
• --all selects every corpus project supported by the adapter;
• --max-cost SECONDS selects a useful subset within an estimated runtime budget; and
• --project URL compares against one ad-hoc target repository instead of the packaged corpus.

Reading the result

Reports also record the exact detector revisions, corpus pins, environment and dependency differences, requested refs or commands, timing, and isolation status needed to interpret or reproduce the comparison.

Explore a report in the browser

Write the complete JSON report alongside the terminal output:

liveness-primer run --tool vulture \
  --repo https://github.com/jendrikseipp/vulture \
  --old v2.15 \
  --new v2.16 \
  --all \
  --output text \
  --json-out liveness-primer-report.json

Then open the static report explorer and choose liveness-primer-report.json. The report is processed locally in the browser rather than uploaded to an application server. The explorer can:

• search, filter, group, and sort findings;
• compare base and head analyzer output with pinned source evidence;
• select or hide findings while reviewing a large change;
• preserve review state in a versioned JSON record; and
• export a focused Markdown or JSON handoff.

To build and serve the explorer locally:

cd explorer
npm ci
npm run build
npm run serve

Open http://127.0.0.1:4173/liveness-primer/explorer/. See explorer/README.md for development and verification commands.

GitHub Actions

The following workflow runs on detector pull requests. It writes a compact human report to the GitHub step summary and uploads the complete JSON report for the explorer, automation, or later review.

name: Liveness Primer

on:
  pull_request:

concurrency:
  group: liveness-primer-${{ github.event.pull_request.number }}
  cancel-in-progress: true

env:
  LIVENESS_PRIMER_REF: main
  PYTHON_VERSION: "3.13"

permissions:
  contents: read

jobs:
  skylos:
    name: Skylos blast radius
    runs-on: ubuntu-latest
    timeout-minutes: 45
    steps:
      - name: Check out liveness_primer
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0  # v7.0.0
        with:
          repository: mcdigman/liveness_primer
          ref: ${{ env.LIVENESS_PRIMER_REF }}
          path: _liveness_primer
          persist-credentials: false

      - name: Install uv
        uses: astral-sh/setup-uv@37802adc94f370d6bfd71619e3f0bf239e1f3b78  # v7.6.0
        with:
          enable-cache: true
          python-version: ${{ env.PYTHON_VERSION }}
          cache-dependency-glob: _liveness_primer/pyproject.toml

      - name: Compare Skylos revisions across the corpus
        run: |
          set -o pipefail
          uvx --from ./_liveness_primer \
            liveness-primer run \
            --tool skylos \
            --repo "${{ github.server_url }}/${{ github.repository }}" \
            --old "${{ github.event.pull_request.base.sha }}" \
            --new "${{ github.event.pull_request.head.sha }}" \
            --all \
            --output github \
            --json-out liveness-primer-report.json \
            --jobs 2 \
            --timeout 300 \
            | tee liveness-primer-report.md >> "$GITHUB_STEP_SUMMARY"

      - name: Upload liveness_primer report
        if: ${{ always() }}
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a  # v7.0.1
        with:
          name: liveness-primer-report
          path: |
            liveness-primer-report.md
            liveness-primer-report.json
          if-no-files-found: error

Detector crashes, timeouts, and unparseable output fail the run without an extra gate. --fail-on adds project-specific regression policy and is repeatable:

• --fail-on new, dropped, or changed rejects that diff class;
• --fail-on any requires the normalized finding set to remain unchanged; and
• --fail-on corpus-integrity rejects corpus-integrity warnings.

For a new feature, leaving finding-diff gates off makes CI an evidence-producing review job. For a semantics-preserving refactor, --fail-on any turns the same workflow into a strict regression gate.

Instead of or in addition to the step summary, a workflow can post a compact digest as a pull-request comment and link reviewers to the complete report and JSON artifact:

LLM-assisted triage

The complete JSON report is also suitable as input to an LLM-assisted review step. A downstream job can group changes by project or rule, highlight large or surprising clusters, call out detector failures, suggest which changes need human attention, and post an advisory digest as a pull-request comment.

Keep the versioned JSON artifact as the source of truth and link every digest back to it. Finding messages and source excerpts originate in detector output and analyzed repositories, so treat them as untrusted content: run the model step without release credentials or unnecessary write permissions, and do not let generated prose replace deterministic gates or human review.

Example simulated LLM-assisted triage digest

Pre-built detector commands

The escape hatch compares commands you have already built:

liveness-primer run --tool vulture \
  --project https://github.com/pytest-dev/pluggy \
  --old-cmd 'vulture-old' \
  --new-cmd 'vulture-new'

Because the primer did not construct and verify these detector environments, the report marks the run as non-comparable and records that isolation was not enforced. --fail-on refuses to gate an escape-hatch run; use this mode for trusted local investigation, not as a managed CI substitute.

Output and exit codes

--output text produces terminal-oriented output, --output github produces GitHub-flavored Markdown, and --output json writes the report to standard output. --json-out PATH archives the complete JSON report alongside any of those display modes.

Exit codes are:

• 0: comparison completed and no enabled gate fired;
• 1: run or configuration failure, including detector invocation failures;
• 2: command-line usage error; and
• 3: an enabled --fail-on gate fired.

Corpus and schema maintenance

liveness-primer corpus validate
liveness-primer corpus license-check
liveness-primer schema export