Contributing to Flutter
See also: Flutter's code of conduct
We gladly accept contributions via GitHub pull requests.
Please become familiar with our style guide and design philosophy. These guidelines are intended to keep the code consistent and avoid common pitfalls, and being familiar with them will make everything much easier for you. If you have questions about our processes or are looking for random tips and tricks, you may be interested in the engine wiki and framework wiki.
This document will introduce you to the basic steps for developing for the Flutter framework (Dart).
If you're interested in developing for the Flutter engine (C++, Java, Objective C), please
switch to the engine repo's
If you have an itch, work on that. If you are just looking for something good to start with, consider the issues marked "easy fix" in our issues list.
Things you will need
- Linux, Mac OS X, or Windows
- git (used for source version control).
- An IDE. We recommend Android Studio with the Flutter plugin.
- An ssh client (used to authenticate with GitHub).
- Python (used by some of our tools).
- The Android platform tools (see Issue #55
about downloading the Android platform tools automatically).
If you're also working on the Flutter engine, you can use the
copy of the Android platform tools in
brew cask install android-platform-tools
sudo apt-get install android-tools-adb
Getting the code and configuring your environment
- Ensure all the dependencies described in the previous section, in particular
git, ssh, and python are installed. Ensure that
adb(from the Android platform tools) is in your path (e.g., that
which adbprints sensible output).
https://github.com/flutter/flutterinto your own GitHub account. If you already have a fork, and are now installing a development environment on a new machine, make sure you've updated your fork so that you don't use stale configuration options from long ago.
- If you haven't configured your machine with an SSH key that's known to github then follow the directions here: https://help.github.com/articles/generating-ssh-keys/.
git clone email@example.com:<your_name_here>/flutter.git
git remote add upstream firstname.lastname@example.org:flutter/flutter.git(So that you fetch from the master repository, not your clone, when running
git fetchet al.)
- Add this repository's
bindirectory to your path. That will let you use the
fluttercommand in this directory more easily.
flutter update-packagesThis will fetch all the Dart packages that Flutter depends on. You can replicate what this script does by running
pub getin each directory that contains a
- If you plan on using IntelliJ as your IDE, then also run
flutter ide-config --overwriteto create all of the IntelliJ configuration files so you can open the main flutter directory as a project and run examples from within the IDE.
Running the examples
To run an example, switch to that example's directory, and use
Make sure you have an emulator running, or a device connected over USB and
debugging enabled on that device.
You can also specify a particular Dart file to run if you want to run an example
that doesn't have a
lib/main.dart file using the
-t command-line option. For
example, to run the
widgets/spinning_square.dart example in the examples/layers
directory on a connected Android device, from that directory you would run:
flutter run -t widgets/spinning_square.dart
When running code from the examples directory, any changes you make to the
example code, as well as any changes to Dart code in the
packages/flutter directory and subdirectories, will
automatically be picked when you relaunch the app. You can do the same for your
own code by mimicking the
pubspec.yaml files in the
Running the analyzer
When editing Flutter code, it's important to check the code with the
analyzer. There are two main ways to run it. In either case you will
want to run
flutter update-packages first, or you will get bogus
error messages about core classes like Offset from
For a one-off, use
flutter analyze --flutter-repo. This uses the
at the root of the repository for its configuration.
For continuous analysis, use
flutter analyze --flutter-repo --watch. This uses normal
analysis_options.yaml files, and they can differ from package to package.
If you want to see how many members are missing dartdocs, you should use the first option,
providing the additional command
If you omit the
--flutter-repo option you may end up in a confusing state because that will
assume you want to check a single package and the flutter repository has several packages.
Running the tests
To automatically find all files named
_test.dart inside a package's
test/ subdirectory, and
run them inside the flutter shell as a test, use the
flutter test command, e.g:
Individual tests can also be run directly, e.g.
flutter test lib/my_app_test.dart
flutter test runs tests inside the flutter shell. To debug tests in Observatory, use the
option to start the test in a paused state and wait for connection from a debugger. This option lets you
set breakpoints before the test runs.
To run analysis and all the tests for the entire Flutter repository, the same way that Cirrus runs them, run
dart dev/bots/test.dart and
If you've built your own flutter engine, you
--local-engine to change what flutter shell
flutter test uses. For example,
if you built an engine in the
out/host_debug_unopt directory, you can pass
--local-engine=host_debug_unopt to run the tests in that engine.
Flutter tests are headless, you won't see any UI. You can use
Adding a test
To add a test to the Flutter package, create a file whose name
_test.dart in the
packages/flutter/test directory. The
test should have a
main function and use the
Working with flutter tools
The flutter tool itself is built when you run
flutter for the first time and each time
flutter upgrade. If you want to alter and re-test the tool's behavior itself,
locally commit your tool changes in git and the tool will be rebuilt from Dart sources
packages/flutter_tools the next time you run
Alternatively, delete the
bin/cache/flutter_tools.snapshot file. Doing so will
force a rebuild of the tool from your local sources the next time you run
flutter_tools' tests run inside the Dart command line VM rather than in the
flutter shell. To run the tests, ensure that no devices are connected,
then navigate to
flutter_tools and execute:
../../bin/cache/dart-sdk/bin/pub run test -j1
The pre-built flutter tool runs in release mode with the observatory off by default.
To enable debugging mode and the observatory on the
flutter tool, uncomment the
FLUTTER_TOOL_ARGS line in the
bin/flutter shell script.
To start working on a patch:
git fetch upstream
git checkout upstream/master -b name_of_your_branch
- Hack away.
git commit -a -m "<your informative commit message>"
git push origin name_of_your_branch
To send us a pull request:
git pull-request(if you are using Hub) or go to
https://github.com/flutter/flutterand click the "Compare & pull request" button
Please make sure all your checkins have detailed commit messages explaining the patch.
Once you've gotten an LGTM from a project maintainer and once your PR has received
the green light from all our automated testing (running on Cirrus, etc), and once
the tree is green (see the design principles
document for more details), submit your changes to the
master branch using one of
the following methods:
- Wait for one of the project maintainers to submit it for you.
- Click the green "Merge pull request" button on the GitHub UI of your pull request (requires commit access)
You must complete the Contributor License Agreement. You can do this online, and it only takes a minute. If you've never submitted code before, you must add your (or your organization's) name and contact info to the AUTHORS file.
We grant commit access to people who have gained our trust and demonstrated a commitment to Flutter.
Tools for tracking and improving test coverage
We strive for a high degree of test coverage for the Flutter framework. We use Coveralls to track our test coverage. You can download our current coverage data from cloud storage and visualize it in Atom as follows:
- Install Atom.
- Install the lcov-info package for Atom.
- Open the
packages/flutterfolder in Atom.
- Open a Dart file in the
libdirectory an type
Ctrl+Alt+Cto bring up the coverage data.
If you don't see any coverage data, check that you have an
lcov.info file in
packages/flutter/coverage directory. It should have been downloaded by the
flutter update-packages command you ran previously.
If you want to iterate quickly on improving test coverage, consider using this workflow:
- Open a file and observe that some line is untested.
- Write a test that exercises that line.
flutter test --merge-coverage path/to/your/test_test.dart.
- After the test passes, observe that the line is now tested.
This workflow merges the coverage data from this test run with the base coverage
data downloaded by
See issue 4719 for ideas about how to improve this workflow.
Working on the engine and the framework at the same time
You can work both with this repository (flutter.git) and the Flutter engine repository at the same time using the following steps.
Follow the instructions above for creating a working copy of this repository.
Follow the contributing instructions in the engine repository to create a working copy of the engine. The instructions also explain how to use a locally-built engine instead of the one bundled with your installation of the Flutter framework.
Making a breaking change to the engine
If you make a breaking change to the engine, you'll need to land your change in a few steps:
Land your change in the engine repository.
Publish a new version of the engine that contains your change. See the engine's release process for instructions about how to publish a new version of the engine. Publishing a new version is important in order to not break folks using prebuilt binaries in their workflow (e.g., our customers).
API docs for master branch
To view the API docs for the
Those docs should be updated after a successful CI build
(Looking for the API docs for our releases? Please visit https://docs.flutter.io.)
We build and test Flutter on: