README.md

# Monorepo

## A gclient solution for checking out Dart and Flutter source trees

Monorepo is:

  * **Optimized for Tip-of-Tree testing**:
  The Monorepo DEPS used to check out Dart and Flutter dependencies comes
  from the Flutter engine DEPS with updated dependencies from Dart.

## Checking out Monorepo

With depot_tools installed and on your path, create a directory for
your monorepo checkout and run these commands to create a gclient solution
in that directory:

```bash
mkdir monorepo
cd monorepo
gclient config --unmanaged https://dart.googlesource.com/monorepo
gclient sync -D
```

This gives you a checkout in the monorepo directory that contains:

```asciidoc
monorepo/
  DEPS - the DEPS used for this gclient checkout
  commits.json - the pinned commits for Dart, flutter/engine,
                 and flutter/flutter
  tools/ - scripts used to create monorepo DEPS
engine/src/ - the flutter/buildroot repo
    flutter/ - the flutter/engine repo
    out/ - the build directory, where Flutter engine builds are created
    third_party/ - Flutter dependencies checked out by DEPS
      dart/ - the Dart SDK checkout.
        third_party - Dart dependencies, also used by Flutter
flutter/ - the flutter/flutter repo
```

## Building Flutter engine

Flutter's instructions for building the engine are at
[Compiling the engine](
https://github.com/flutter/flutter/wiki/Compiling-the-engine)

They can be followed closely, with a few changes:

  * Googlers working on Dart do not need to switch to Fuchsia's Goma RBE,
    except for Windows. The GOMA_DIR enviroment variable can just point to
    the .cipd_bin directory in a depot_tools installation, and just
    `goma_ctl ensure_start` is sufficient.
  * The --no-prebuilt-dart-sdk option has to be added to every gn command,
    so that the build is set up to build and use a local Dart SDK.
  * The --full-dart-sdk option must be added to gn for the host build target
    if you will be building web or desktop apps.

Example build commands that work on linux:
```shell
MONOREPO_PATH=$PWD
if [[ ! $PATH =~ (^|:)$MONOREPO_PATH/flutter/bin(:|$) ]]; then
  PATH=$MONOREPO_PATH/flutter/bin:$PATH
fi

export GOMA_DIR=$(dirname $(command -v gclient))/.cipd_bin
goma_ctl ensure_start

pushd engine/src
flutter/tools/gn --goma --no-prebuilt-dart-sdk --unoptimized --full-dart-sdk
autoninja -C out/host_debug_unopt
popd
```

## Building Flutter apps

The Flutter commands used to build and run apps will use the locally built
Flutter engine and Dart SDK, instead of the one downloaded by the Flutter tool,
if the `--local-engine` option is provided.

For example, to build and run the
Flutter spinning square sample on the web platform,
```sh
MONOREPO_PATH=$PWD
cd flutter/examples/layers
flutter --local-engine=host_debug_unopt \
  -d chrome run widgets/spinning_square.dart
cd $MONOREPO_PATH
```
To build for desktop, specify the desktop platform device in `flutter run` as
`-d macos` or `-d linux` or `-d windows`.
You may also need to run the command
```sh
flutter create --platforms=windows,macos,linux
```
on existing apps, such as sample apps. New apps created with `flutter create`
already include these support files. Details of desktop support are at
[Desktop Support for Flutter](https://docs.flutter.dev/desktop)

## Testing

Tests in the Flutter source tree can be run with the  `flutter test` command,
run in the directory of a package containing tests. For example:

```sh
MONOREPO_PATH=$PWD
cd flutter/packages/flutter
flutter test --local-engine=host_debug_unopt
cd $MONOREPO_PATH
```

## Troubleshooting

Please file an [issue](https://github.com/dart-lang/sdk/issues/new?labels=area-infrastructure,monorepo&title=Monorepo+suggestion&assignees=whesse&body=I+suggest+that+...)
or email the dart-engprod team with any problems with or questions about
using monorepo.

We will update this documentation to address them.

  * `flutter` commands may download the engine and Dart SDK files for
    the configured channel, even though they will be using the local engine
    and its SDK.

### Windows

  * On Windows, `gclient sync` needs to be run in an administrator session,
    because some installed dependencies create symlinks.