channel-watch.yml

name: watch for flutter updates

on:
  # Check every 15 minutes
  schedule:    
    - cron: "*/15 * * * *"

  push:
    branches: [ ci ]
  pull_request:
    branches: [ ci ]

  workflow_dispatch:

jobs:
  check-for-roll:
    name: 'Check if stable engine commit changed'
    runs-on: ubuntu-latest
    outputs:
      changed: ${{ steps.check-roll.outputs.changed }}

    steps:
      - uses: actions/checkout@v3
        with:
          # We need to use a custom token here to be able to push commits.
          token: ${{ secrets.ENGINE_ROLL_TOKEN }}
      
      # If we only want to find out the stable engine version, we can do `wget -O engine.version.stable https://raw.githubusercontent.com/flutter/flutter/stable/bin/internal/engine.version`
      # However we also want to find out the semver of the flutter release (3.0.5 for example), 
      - name: Download latest engine.version
        run: wget -O engine.version.stable https://raw.githubusercontent.com/flutter/flutter/stable/bin/internal/engine.version
      
      - name: Check if stable engine version changed 
        id: check-roll
        run: |
          git status
          if git diff-index --quiet HEAD -- engine.version.stable; then
            echo "No changes"
            echo "changed=false" >> $GITHUB_OUTPUT
          else
            echo "Delta"
            echo "changed=true" >> $GITHUB_OUTPUT
          fi
      
      - name: Log
        run: |
          echo '*** Stable engine commit changed? ***'
          echo steps.check-roll.outputs.changed: ${{ steps.check-roll.outputs.changed }}
      
      # reference: https://github.com/flutter/flutter/blob/a880c4ed3590477380c975f867406ba336834848/packages/flutter_tools/lib/src/version.dart#L703
      # if the flutter people ever decide to point more than one tags at the stable SDK commit we're in trouble here
      - name: find out flutter SDK semver for this engine version
        id: flutter-version
        if: ${{ steps.check-roll.outputs.changed == 'true' }}
        run: |
          # read the engine.version.stable file to find the engine commit hash
          # we're build for
          ENGINE_HASH=$(cat engine.version.stable | tr -dc [:xdigit:])
          
          echo "hash=$ENGINE_HASH" >> $GITHUB_OUTPUT
      
      - name: Commit new stable engine version
        # the if is not really necessary since the add-and-commit action won't push empty commits, but this way it feels safer
        # (it won't even push the tag if we have an empty commit)
        if: ${{ steps.check-roll.outputs.changed == 'true' }}
        uses: EndBug/add-and-commit@v9
        with:
          default_author: github_actions
          message: 'Roll engine (stable)'
          add: 'engine.version.stable'
          tag: engine/${{ steps.flutter-version.outputs.hash }} --force
          tag_push: '--force'