Monorepo engine buidls

monorepo.md

Below is an example GitHub Actions workflow updated for the new monorepo structure, where the former Engine repository now resides inside an engine/ folder in the main Flutter repository. This assumes you still want to build the native engine artifacts (e.g., for Linux, Windows, macOS, iOS, Android, Web) using GN + Ninja (i.e., the Chromium-based build system).

Important: The monorepo is still in flux as of this writing. The steps below might require adjustments based on the latest official instructions from the Flutter repository. The general ideas—installing depot_tools, running gclient sync, running gn gen, and then ninja—remain the same, but you may need to tweak paths and GN args.

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1. Workflow Overview

1. Check out the main Flutter repo (which contains engine/ folder).
2. Install dependencies needed for building the engine, including depot_tools.
3. Navigate into the engine folder.
4. Sync dependencies with gclient sync.
5. Generate build files via gn gen.
6. Build using ninja.
7. Repeat for each combination of platform + build mode as needed.

Below is an example of a single YAML file that runs a matrix build for multiple platforms and build modes (debug, profile, release). Customize to your needs.

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2. Example Workflow File

Create a file (for example, .github/workflows/build_engine.yml) with the following contents:

name: Build Flutter Engine (Monorepo)

on:
  push:
    branches: [ "main" ]
  pull_request:
    branches: [ "main" ]

jobs:
  # -------------------------------------------------------------------
  # 1) Build on Linux
  # -------------------------------------------------------------------
  build-linux:
    name: Build Engine on Linux
    runs-on: ubuntu-latest
    strategy:
      matrix:
        build_mode: [debug, profile, release]
    steps:
      - name: Check out Flutter repo
        uses: actions/checkout@v3
        with:
          # If your repo still uses submodules, you may need this:
          # submodules: true
          # fetch-depth: 0 (if you need full history)
          fetch-depth: 0

      - name: Install dependencies
        run: |
          sudo apt-get update
          sudo apt-get install -y curl python3 python3-pip python3-setuptools git clang cmake ninja-build pkg-config
          
          # Clone depot_tools to get gclient, gn, ninja, etc.
          git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git $HOME/depot_tools
          echo "::add-path::$HOME/depot_tools"

      - name: Sync dependencies (gclient sync)
        working-directory: engine
        run: |
          # Run gclient sync from within the engine folder
          gclient sync

      - name: Generate GN build files
        working-directory: engine
        run: |
          # We'll name our build output directory based on mode + platform
          gn gen out/linux_${{ matrix.build_mode }} \
            --args="is_debug=${{ matrix.build_mode == 'debug' }} \
                    is_profile=${{ matrix.build_mode == 'profile' }} \
                    target_os=\"linux\""

      - name: Build flutter engine
        working-directory: engine
        run: |
          ninja -C out/linux_${{ matrix.build_mode }} flutter


  # -------------------------------------------------------------------
  # 2) Build on Windows
  # -------------------------------------------------------------------
  build-windows:
    name: Build Engine on Windows
    runs-on: windows-latest
    strategy:
      matrix:
        build_mode: [debug, profile, release]
    steps:
      - name: Check out Flutter repo
        uses: actions/checkout@v3
        with:
          fetch-depth: 0

      - name: Install dependencies
        run: |
          choco install python --version=3.9.0 -y
          choco install visualstudio2022buildtools -y
          choco install cmake ninja git -y
          
          # Set up depot_tools
          git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git C:\depot_tools
          echo "C:\\depot_tools" >> $env:GITHUB_PATH

      - name: Sync dependencies (gclient sync)
        run: |
          cd engine
          gclient sync

      - name: Generate GN build files
        run: |
          cd engine
          gn gen out\windows_${{ matrix.build_mode }} --args="is_debug=${{ matrix.build_mode == 'debug' }} is_profile=${{ matrix.build_mode == 'profile' }} target_os=\"win\""

      - name: Build flutter engine
        run: |
          cd engine
          ninja -C out\windows_${{ matrix.build_mode }} flutter


  # -------------------------------------------------------------------
  # 3) Build on macOS (and optionally iOS)
  # -------------------------------------------------------------------
  build-macos:
    name: Build Engine on macOS
    runs-on: macos-latest
    strategy:
      matrix:
        build_mode: [debug, profile, release]
    steps:
      - name: Check out Flutter repo
        uses: actions/checkout@v3
        with:
          fetch-depth: 0

      - name: Install dependencies
        run: |
          brew update
          brew install python git ninja cmake
          
          # depot_tools
          git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git $HOME/depot_tools
          echo "::add-path::$HOME/depot_tools"

      - name: Sync dependencies (gclient sync)
        working-directory: engine
        run: |
          gclient sync

      - name: Generate GN build files
        working-directory: engine
        run: |
          gn gen out/mac_${{ matrix.build_mode }} \
            --args="is_debug=${{ matrix.build_mode == 'debug' }} \
                    is_profile=${{ matrix.build_mode == 'profile' }} \
                    target_os=\"mac\""

      - name: Build flutter engine
        working-directory: engine
        run: |
          ninja -C out/mac_${{ matrix.build_mode }} flutter


  # -------------------------------------------------------------------
  # (Optional) Build iOS
  # -------------------------------------------------------------------
  build-ios:
    name: Build Engine on iOS
    runs-on: macos-latest
    strategy:
      matrix:
        build_mode: [debug, profile, release]
    steps:
      - name: Check out Flutter repo
        uses: actions/checkout@v3
        with:
          fetch-depth: 0

      - name: Install dependencies
        run: |
          brew update
          brew install python git ninja cmake
          
          # depot_tools
          git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git $HOME/depot_tools
          echo "::add-path::$HOME/depot_tools"

      - name: Sync dependencies (gclient sync)
        working-directory: engine
        run: |
          gclient sync

      - name: Generate GN build files
        working-directory: engine
        run: |
          # Customize for iOS device vs iOS simulator as needed
          gn gen out/ios_${{ matrix.build_mode }} \
            --args="is_debug=${{ matrix.build_mode == 'debug' }} \
                    is_profile=${{ matrix.build_mode == 'profile' }} \
                    target_os=\"ios\""

      - name: Build flutter engine
        working-directory: engine
        run: |
          ninja -C out/ios_${{ matrix.build_mode }} flutter


  # -------------------------------------------------------------------
  # (Optional) Build Android
  # -------------------------------------------------------------------
  build-android:
    name: Build Engine on Android
    runs-on: ubuntu-latest
    strategy:
      matrix:
        build_mode: [debug, profile, release]
    steps:
      - name: Check out Flutter repo
        uses: actions/checkout@v3
        with:
          fetch-depth: 0

      - name: Install dependencies
        run: |
          sudo apt-get update
          sudo apt-get install -y curl python3 python3-pip python3-setuptools git clang cmake ninja-build pkg-config default-jdk
          
          # Android SDK/NDK setup if needed
          # e.g., install a specific NDK version, set environment variables, etc.
          
          # depot_tools
          git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git $HOME/depot_tools
          echo "::add-path::$HOME/depot_tools"

      - name: Sync dependencies (gclient sync)
        working-directory: engine
        run: |
          gclient sync

      - name: Generate GN build files
        working-directory: engine
        run: |
          gn gen out/android_${{ matrix.build_mode }} \
            --args="is_debug=${{ matrix.build_mode == 'debug' }} \
                    is_profile=${{ matrix.build_mode == 'profile' }} \
                    target_os=\"android\""

      - name: Build flutter engine
        working-directory: engine
        run: |
          ninja -C out/android_${{ matrix.build_mode }} flutter


  # -------------------------------------------------------------------
  # (Optional) Build Web (WASM target)
  # -------------------------------------------------------------------
  build-web:
    name: Build Engine on Web
    runs-on: ubuntu-latest
    strategy:
      matrix:
        build_mode: [debug, profile, release]
    steps:
      - name: Check out Flutter repo
        uses: actions/checkout@v3
        with:
          fetch-depth: 0

      - name: Install dependencies
        run: |
          sudo apt-get update
          sudo apt-get install -y curl python3 python3-pip python3-setuptools git clang cmake ninja-build pkg-config
          
          # depot_tools
          git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git $HOME/depot_tools
          echo "::add-path::$HOME/depot_tools"

      - name: Sync dependencies (gclient sync)
        working-directory: engine
        run: |
          gclient sync

      - name: Generate GN build files
        working-directory: engine
        run: |
          gn gen out/web_${{ matrix.build_mode }} \
            --args="is_debug=${{ matrix.build_mode == 'debug' }} \
                    is_profile=${{ matrix.build_mode == 'profile' }} \
                    target_os=\"wasm\""

      - name: Build flutter engine
        working-directory: engine
        run: |
          ninja -C out/web_${{ matrix.build_mode }} flutter

Notes and Adjustments

1. Working Directory

   • We’re specifying working-directory: engine (or cd engine) before calling gclient sync, gn gen, or ninja. This is crucial now that the Engine code lives in engine/.
   • If your local layout or build instructions differ, you may need to adjust paths accordingly.

2. gclient sync and DEPS

   • In the monorepo, the DEPS file may have changed. You still need to run gclient sync from within the engine/ folder to download any additional third-party dependencies.
   • You might also need to run gclient config if your local environment is not set up with .gclient or if the config is missing.

3. GN Args

   • The --args shown here are simplified. You may need additional flags like enable_fontconfig, use_dart_zip, or something else based on your needs. Check the monorepo’s updated build docs for the latest recommended flags.

4. Caching

   • Consider adding GitHub Actions caching for ~/.pub-cache, ~/.gradle, ~/.dartServer, or even the out/ directory to speed up builds. Be careful with caching built artifacts though, as partial/incompatible caches can cause sporadic failures.

5. Artifacts

   • If you want to distribute or test your built engine artifacts, you might want to upload artifacts or push them to a custom storage location. For example:

     - name: Upload built artifacts
       uses: actions/upload-artifact@v3
       with:
         name: flutter-engine-${{ matrix.build_mode }}-linux
         path: engine/out/linux_${{ matrix.build_mode }}

6. Android & iOS

   • For iOS, you need Xcode installed (which macos-latest generally provides).
   • For Android, you typically need the SDK + NDK. This example does not fully demonstrate setting up the correct NDK versions or environment variables. Adapt as needed.

---

3. Wrapping Up

With the above workflow:

• You build multiple platforms (Linux, Windows, macOS, iOS, Android, Web) in parallel via GitHub Actions.
• You build multiple modes (debug, profile, release) via the matrix.
• You run gclient sync in the engine/ subdirectory to pull in dependencies.
• You use gn gen and ninja to compile the engine targets.

You’ll almost certainly need to tweak the commands for your own environment, but this provides a template to get started building the Flutter Engine code in the new monorepo structure. Good luck!