visual-difference-detection.yml

name: Visual difference detection
# This workflow performs visual comparisons between the main branch and a pull request.
# It activates when the "visual-comparison-required" label is added to a pull request.
#
# KEY POINTS:
# - Activation:         The workflow triggers only when the "visual-comparison-required" label is added.
# - Trigger Conditions: Subsequent commits or amendments to the pull request will not trigger the workflow again.
#                       To re-trigger, remove and add again the "visual-comparison-required" label.
# - Label Handling:     Other labels can also activate the workflow. However, the workflow will halt if the "visual-comparison-required" label is missing.
# - Caution:            If the "visual-comparison-required" label is present, adding other labels will still trigger and execute the entire workflow.

on:
  pull_request:
    types: [ labeled ]

jobs:
  check-label:
    # Checks if the "visual-comparison-required" label is present on the pull request.
    # The remaining jobs will only run if this label is found.
    name: Check for "visual-comparison-required" label
    runs-on: ubuntu-latest
    outputs:
      visual-comparison-required-label-found: ${{ steps.check.outputs.visual-comparison-required-label-found }}
    steps:
      - name: Check out repository
        uses: actions/checkout@v4
      - name: Check for "visual-comparison-required" label
        id: check
        env:
          VISUAL_COMPARISON_REQUIRED_LABEL_PRESENT: ${{ contains(github.event.pull_request.labels.*.name, 'visual-comparison-required') }}
        run: |
          echo "visual-comparison-required-label-found=$VISUAL_COMPARISON_REQUIRED_LABEL_PRESENT" | tee "$GITHUB_OUTPUT"

  take-screenshots-main:
    # This job takes screenshots of the main branch for visual comparison.
    # It runs only if the "visual-comparison-required" label is found.
    name: Take screenshots (main branch)
    needs: check-label
    if: needs.check-label.outputs.visual-comparison-required-label-found == 'true'
    runs-on: ubuntu-latest
    steps:
      # We switch to the main branch to take the screenshots
      - name: Check out repository code
        uses: actions/checkout@v4
        with:
          ref: main
      - name: Use Node.js
        uses: actions/setup-node@v3
        with:
          node-version: current
      - name: Install dependencies
        run: yarn install --frozen-lockfile
      - name: Install Playwright browsers
        run: yarn playwright install --with-deps chromium
      - name: Build the website
        run: yarn docusaurus build
      - name: Take screenshots with Playwright
        run: yarn workspace argos screenshot
      # Argos needs two extra pieces of information to associate screenshots with the branch.
      # - We have to set the ARGOS_BRANCH variable to main, so that it could be labelled properly in the UI
      # - We have to set the ARGOS_COMMIT variable to the main branch commit sha. It is necessary, because Argos
      #   uses this information to make sure the screenshots for comparison are the ancestors of the version
      #   in the pull request
      - name: Store the main branch sha in GitHub environmental variables
        run: echo "ARGOS_COMMIT=$(git rev-parse HEAD)" >> $GITHUB_ENV
      - name: Upload screenshots to Argos
        run: yarn workspace argos upload
        env:
          ARGOS_BRANCH: main
          ARGOS_COMMIT: ${{ env.ARGOS_COMMIT }}

  take-screenshots-pull-request:
    # This job takes screenshots of the pull request branch for visual comparison.
    # It runs only if the "visual-comparison-required" label is found.
    name: Take screenshots (pull request branch)
    needs: [check-label, take-screenshots-main]
    if: needs.check-label.outputs.visual-comparison-required-label-found == 'true'
    runs-on: ubuntu-latest
    steps:
      - name: Check out repository code
        uses: actions/checkout@v4
      - name: Use Node.js
        uses: actions/setup-node@v3
        with:
          node-version: current
      - name: Install dependencies
        run: yarn install --frozen-lockfile
      - name: Install Playwright browsers
        run: yarn playwright install --with-deps chromium
      - name: Build the website
        run: yarn docusaurus build
      - name: Take screenshots with Playwright
        run: yarn workspace argos screenshot
      - name: Upload screenshots to Argos
        run: yarn workspace argos upload