Run mypy via pre-commit + reviewdog

This GitHub Action runs mypy via pre-commit on a ref range and reports diagnostics to pull requests using reviewdog, using RDJSON as the intermediate format.

It uses the mypy-json-output hook to produce JSON lines, then converts them to RDJSON via a jq script.

Requirements

Add the mypy hooks to your .pre-commit-config.yaml:

repos:
  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v1.19.0
    hooks:
      - id: mypy
        additional_dependencies:
          # add stubs the project needs
          - types-requests
          - types-setuptools
      - id: mypy
        alias: mypy-json-output
        name: mypy (json output)
        args:
          [
            "--output",
            "json",
            "--hide-error-context",
            "--show-column-numbers",
            "--show-absolute-path",
            "--no-pretty",
            "--ignore-missing-imports",
            "--scripts-are-modules",
          ]
        additional_dependencies:
          # add stubs the project needs
          - types-requests
          - types-setuptools
        stages: [manual]

You also need:

• GitHub Actions enabled on the repository
• secrets.GITHUB_TOKEN available (default on GitHub-hosted runners)
• A runner with jq available
• The jq filter file at lib/mypy-json-to-rdjson.jq in this action repository
• actions/checkout fetching enough history to include both from-ref and to-ref, for example:

- uses: actions/checkout@v4
  with:
    fetch-depth: 0

Inputs

Name	Required	Description
from-ref	✅	Base git ref (e.g. PR base SHA)
to-ref	✅	Head git ref (e.g. PR head SHA)
github-token	✅	GitHub token for reviewdog (secrets.GITHUB_TOKEN)

Outputs

Name	Description
exitcode	Exit code returned by the mypy-json-output hook

Usage

Example workflow for pull requests:

name: Type-check with mypy

on:
  pull_request:

jobs:
  mypy:
    runs-on: ubuntu-latest

    steps:
      - name: Checkout
        uses: actions/checkout@v4
        with:
          fetch-depth: 0

      - name: Run mypy via pre-commit + reviewdog
        uses: leinardi/gha-pre-commit-mypy-reviewdog@v1
        with:
          from-ref: ${{ github.event.pull_request.base.sha }}
          to-ref: ${{ github.event.pull_request.head.sha }}
          github-token: ${{ secrets.GITHUB_TOKEN }}

This will:

1. Run mypy-json-output on the files changed between from-ref and to-ref.
2. Convert the JSONL output to RDJSON using the provided jq script.
3. Report diagnostics as inline comments on the pull request via reviewdog.
4. Fail the job if type errors are found.

Versioning

It’s recommended to pin to the major version:

uses: leinardi/gha-pre-commit-mypy-reviewdog@v1

For fully reproducible behavior, pin to an exact tag:

uses: leinardi/gha-pre-commit-mypy-reviewdog@v1.0.0