diff-shades workflow (psf/black)

The diff-shades workflow from psf/black, explained and optimized by Latchkey.

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Source: psf/black.github/workflows/diff_shades.ymlLicense MITView source

What it does

This is the diff-shades workflow from the psf/black repository, a real project running GitHub Actions. It is shown here with attribution under its MIT license.

Below, Latchkey shows a faster, safer version produced by its optimization engine.

The workflow

workflow (.yml)

name: diff-shades

on:
  push:
    branches: [main]
    paths:
      - src/**
      - pyproject.toml
      - scripts/diff_shades_gha_helper.py
      - .github/workflows/diff_shades.yml
      - .github/workflows/diff_shades_comment.yml

  pull_request:
    paths:
      - src/**
      - pyproject.toml
      - scripts/diff_shades_gha_helper.py
      - .github/workflows/diff_shades.yml
      - .github/workflows/diff_shades_comment.yml

concurrency:
  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}
  cancel-in-progress: true

env:
  HATCH_BUILD_HOOKS_ENABLE: "1"
  # Clang is less picky with the C code it's given than gcc (and may generate faster
  # binaries too).
  CC: clang-18

permissions: {}

jobs:
  configure:
    runs-on: ubuntu-latest
    outputs:
      matrix: ${{ steps.set-config.outputs.matrix }}

    steps:
      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          persist-credentials: false

      - name: Set up Python
        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
        with:
          python-version: "3.14"
          pip-version: "25.3"
          pip-install: --group diff-shades --group diff-shades-comment

      - name: Calculate run configuration & metadata
        id: set-config
        env:
          GITHUB_TOKEN: ${{ github.token }}
        run: python scripts/diff_shades_gha_helper.py config

  analysis-base:
    name: analysis / base / ${{ matrix.mode }}
    needs: configure
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        include: ${{ fromJson(needs.configure.outputs.matrix) }}

    steps:
      - name: Checkout this repository (full clone)
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          # The baseline revision could be rather old so a full clone is ideal.
          fetch-depth: 0
          persist-credentials: false

      - name: Set up Python
        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
        with:
          python-version: "3.14"
          pip-version: "25.3"
          pip-install: --group diff-shades

      - name: Configure git
        run: |
          git config user.name "diff-shades-gha"
          git config user.email "diff-shades-gha@example.com"

      - name: Attempt to use cached baseline analysis
        id: baseline-cache
        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
        with:
          path: ${{ matrix.baseline-analysis }}
          key: ${{ matrix.baseline-cache-key }}

      - name: Build and install baseline revision
        if: steps.baseline-cache.outputs.cache-hit != 'true'
        env:
          GITHUB_TOKEN: ${{ github.token }}
        run: |
          ${{ matrix.baseline-setup-cmd }}
          python -m pip install .

      - name: Analyze baseline revision
        if: steps.baseline-cache.outputs.cache-hit != 'true'
        run:
          diff-shades analyze ${{ matrix.baseline-analysis }} --work-dir projects-cache/
          --force-${{ matrix.style }}-style -v

      - name: Upload baseline analysis
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: ${{ matrix.baseline-analysis }}
          path: ${{ matrix.baseline-analysis }}

  analysis-target:
    name: analysis / target / ${{ matrix.mode }}
    needs: configure
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        include: ${{ fromJson(needs.configure.outputs.matrix) }}

    steps:
      - name: Checkout this repository (full clone)
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          # The baseline revision could be rather old so a full clone is ideal.
          fetch-depth: 0
          persist-credentials: false

      - name: Set up Python
        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
        with:
          python-version: "3.14"
          pip-version: "25.3"
          pip-install: --group diff-shades

      - name: Configure git
        run: |
          git config user.name "diff-shades-gha"
          git config user.email "diff-shades-gha@example.com"

      - name: Build and install target revision
        env:
          GITHUB_TOKEN: ${{ github.token }}
        run: |
          ${{ matrix.target-setup-cmd }}
          python -m pip install .

      # Pull it from previous runs - we're NOT trying to get it from this run
      # (but it wouldn't cause problems if we theoretically did)
      - name: Attempt to find baseline analysis
        id: baseline-cache
        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
        with:
          path: ${{ matrix.baseline-analysis }}
          key: ${{ matrix.baseline-cache-key }}

      - name: Analyze target revision (with repeated projects)
        if: steps.baseline-cache.outputs.cache-hit == 'true'
        run: |
          diff-shades analyze ${{ matrix.target-analysis }} --work-dir projects-cache/ \
          --force-${{ matrix.style }}-style -v \
          --repeat-projects-from ${{ matrix.baseline-analysis }}

      - name: Analyze target revision (without repeated projects)
        if: steps.baseline-cache.outputs.cache-hit != 'true'
        run:
          diff-shades analyze ${{ matrix.target-analysis }} --work-dir projects-cache/
          --force-${{ matrix.style }}-style -v

      - name: Upload target analysis
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: ${{ matrix.target-analysis }}
          path: ${{ matrix.target-analysis }}

      - name: Check for failed files for target revision
        run: diff-shades show-failed --check --show-log ${{ matrix.target-analysis }}

  compare:
    name: compare / ${{ matrix.mode }}
    needs: ["configure", "analysis-base", "analysis-target"]
    if: ${{ !cancelled() }}
    runs-on: ubuntu-latest
    strategy:
      fail-fast: false
      matrix:
        include: ${{ fromJson(needs.configure.outputs.matrix) }}

    steps:
      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          persist-credentials: false

      - uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
        with:
          merge-multiple: true

      - name: Set up Python
        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
        with:
          python-version: "3.14"
          pip-version: "25.3"
          pip-install: --group diff-shades --group diff-shades-comment

      - name: Generate HTML diff report
        run: |
          diff-shades --dump-html diff.html \
          compare --diff ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }}

      - name: Upload diff report
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: ${{ matrix.style }}-diff.html
          path: diff.html

      - name: Generate summary file (PR only)
        if: github.event_name == 'pull_request'
        env:
          GITHUB_TOKEN: ${{ github.token }}
        run: |
          python scripts/diff_shades_gha_helper.py comment-body \
          ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }} \
          ${{ matrix.style }} ${{ matrix.mode }}

      - name: Upload summary file (PR only)
        if: github.event_name == 'pull_request'
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: .${{ matrix.style }}.pr-comment.md
          path: .${{ matrix.style }}.pr-comment.md
          include-hidden-files: true

      - name: Verify zero changes (PR only)
        if: matrix.mode == 'assert-no-changes'
        run: |
          diff-shades compare --check \
          ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }} || \
          (echo "Please verify you didn't change the stable code style unintentionally!" \
          && exit 1)

The same workflow, on Latchkey

Estimated ~20% faster on cache hits, plus fewer wasted runs and a safer supply chain. Added and changed lines are highlighted.

name: diff-shades
 
on:
  push:
    branches: [main]
    paths:
      - src/**
      - pyproject.toml
      - scripts/diff_shades_gha_helper.py
      - .github/workflows/diff_shades.yml
      - .github/workflows/diff_shades_comment.yml
 
  pull_request:
    paths:
      - src/**
      - pyproject.toml
      - scripts/diff_shades_gha_helper.py
      - .github/workflows/diff_shades.yml
      - .github/workflows/diff_shades_comment.yml
 
concurrency:
  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.run_id }}
  cancel-in-progress: true
 
env:
  HATCH_BUILD_HOOKS_ENABLE: "1"
  # Clang is less picky with the C code it's given than gcc (and may generate faster
  # binaries too).
  CC: clang-18
 
permissions: {}
 
jobs:
  configure:
    timeout-minutes: 30
    runs-on: latchkey-small
    outputs:
      matrix: ${{ steps.set-config.outputs.matrix }}
 
    steps:
      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          persist-credentials: false
 
      - name: Set up Python
        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
        with:
          cache: 'pip'
          python-version: "3.14"
          pip-version: "25.3"
          pip-install: --group diff-shades --group diff-shades-comment
 
      - name: Calculate run configuration & metadata
        id: set-config
        env:
          GITHUB_TOKEN: ${{ github.token }}
        run: python scripts/diff_shades_gha_helper.py config
 
  analysis-base:
    timeout-minutes: 30
    name: analysis / base / ${{ matrix.mode }}
    needs: configure
    runs-on: latchkey-small
    strategy:
      fail-fast: false
      matrix:
        include: ${{ fromJson(needs.configure.outputs.matrix) }}
 
    steps:
      - name: Checkout this repository (full clone)
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          # The baseline revision could be rather old so a full clone is ideal.
          fetch-depth: 0
          persist-credentials: false
 
      - name: Set up Python
        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
        with:
          cache: 'pip'
          python-version: "3.14"
          pip-version: "25.3"
          pip-install: --group diff-shades
 
      - name: Configure git
        run: |
          git config user.name "diff-shades-gha"
          git config user.email "diff-shades-gha@example.com"
 
      - name: Attempt to use cached baseline analysis
        id: baseline-cache
        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
        with:
          path: ${{ matrix.baseline-analysis }}
          key: ${{ matrix.baseline-cache-key }}
 
      - name: Build and install baseline revision
        if: steps.baseline-cache.outputs.cache-hit != 'true'
        env:
          GITHUB_TOKEN: ${{ github.token }}
        run: |
          ${{ matrix.baseline-setup-cmd }}
          python -m pip install .
 
      - name: Analyze baseline revision
        if: steps.baseline-cache.outputs.cache-hit != 'true'
        run:
          diff-shades analyze ${{ matrix.baseline-analysis }} --work-dir projects-cache/
          --force-${{ matrix.style }}-style -v
 
      - name: Upload baseline analysis
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: ${{ matrix.baseline-analysis }}
          path: ${{ matrix.baseline-analysis }}
 
  analysis-target:
    timeout-minutes: 30
    name: analysis / target / ${{ matrix.mode }}
    needs: configure
    runs-on: latchkey-small
    strategy:
      fail-fast: false
      matrix:
        include: ${{ fromJson(needs.configure.outputs.matrix) }}
 
    steps:
      - name: Checkout this repository (full clone)
        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          # The baseline revision could be rather old so a full clone is ideal.
          fetch-depth: 0
          persist-credentials: false
 
      - name: Set up Python
        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
        with:
          cache: 'pip'
          python-version: "3.14"
          pip-version: "25.3"
          pip-install: --group diff-shades
 
      - name: Configure git
        run: |
          git config user.name "diff-shades-gha"
          git config user.email "diff-shades-gha@example.com"
 
      - name: Build and install target revision
        env:
          GITHUB_TOKEN: ${{ github.token }}
        run: |
          ${{ matrix.target-setup-cmd }}
          python -m pip install .
 
      # Pull it from previous runs - we're NOT trying to get it from this run
      # (but it wouldn't cause problems if we theoretically did)
      - name: Attempt to find baseline analysis
        id: baseline-cache
        uses: actions/cache@55cc8345863c7cc4c66a329aec7e433d2d1c52a9 # v6.1.0
        with:
          path: ${{ matrix.baseline-analysis }}
          key: ${{ matrix.baseline-cache-key }}
 
      - name: Analyze target revision (with repeated projects)
        if: steps.baseline-cache.outputs.cache-hit == 'true'
        run: |
          diff-shades analyze ${{ matrix.target-analysis }} --work-dir projects-cache/ \
          --force-${{ matrix.style }}-style -v \
          --repeat-projects-from ${{ matrix.baseline-analysis }}
 
      - name: Analyze target revision (without repeated projects)
        if: steps.baseline-cache.outputs.cache-hit != 'true'
        run:
          diff-shades analyze ${{ matrix.target-analysis }} --work-dir projects-cache/
          --force-${{ matrix.style }}-style -v
 
      - name: Upload target analysis
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: ${{ matrix.target-analysis }}
          path: ${{ matrix.target-analysis }}
 
      - name: Check for failed files for target revision
        run: diff-shades show-failed --check --show-log ${{ matrix.target-analysis }}
 
  compare:
    timeout-minutes: 30
    name: compare / ${{ matrix.mode }}
    needs: ["configure", "analysis-base", "analysis-target"]
    if: ${{ !cancelled() }}
    runs-on: latchkey-small
    strategy:
      fail-fast: false
      matrix:
        include: ${{ fromJson(needs.configure.outputs.matrix) }}
 
    steps:
      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
        with:
          persist-credentials: false
 
      - uses: actions/download-artifact@3e5f45b2cfb9172054b4087a40e8e0b5a5461e7c # v8.0.1
        with:
          merge-multiple: true
 
      - name: Set up Python
        uses: actions/setup-python@ece7cb06caefa5fff74198d8649806c4678c61a1 # v6.3.0
        with:
          cache: 'pip'
          python-version: "3.14"
          pip-version: "25.3"
          pip-install: --group diff-shades --group diff-shades-comment
 
      - name: Generate HTML diff report
        run: |
          diff-shades --dump-html diff.html \
          compare --diff ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }}
 
      - name: Upload diff report
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: ${{ matrix.style }}-diff.html
          path: diff.html
 
      - name: Generate summary file (PR only)
        if: github.event_name == 'pull_request'
        env:
          GITHUB_TOKEN: ${{ github.token }}
        run: |
          python scripts/diff_shades_gha_helper.py comment-body \
          ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }} \
          ${{ matrix.style }} ${{ matrix.mode }}
 
      - name: Upload summary file (PR only)
        if: github.event_name == 'pull_request'
        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
        with:
          name: .${{ matrix.style }}.pr-comment.md
          path: .${{ matrix.style }}.pr-comment.md
          include-hidden-files: true
 
      - name: Verify zero changes (PR only)
        if: matrix.mode == 'assert-no-changes'
        run: |
          diff-shades compare --check \
          ${{ matrix.baseline-analysis }} ${{ matrix.target-analysis }} || \
          (echo "Please verify you didn't change the stable code style unintentionally!" \
          && exit 1)

What changed

Run on Latchkey managed runners with one line (runs-on), which apply the fixes below automatically and self-heal transient failures. This example uses latchkey-small; pick the runner size that fits the job.
Cache dependency installs on the setup step so they are served from cache.
Add a job timeout so a hung step cannot burn hours of runner time.

What Latchkey heals here

This workflow has steps that commonly fail on transient issues (network, registries, flaky browsers). On Latchkey managed runners they are detected, retried, and self-healed instead of failing your build:

Dependency installs

This workflow runs 4 jobs per trigger. On Latchkey the same minutes cost up to 58% less than GitHub-hosted, with zero queue time.

Actions used in this workflow

actions/checkout actions/setup-python actions/cache actions/upload-artifact actions/download-artifact