flutter-embedder.git

The Flutter Embedder for Fuchsia is a new in-progress runtime for Flutter apps on Fuchsia. This runtime is built on top of Flutter's embedder platform.

This repository is a work in progress and should be considered experimental.

Requirements

If you're using WSL2 (Windows Subsystem for Linux), see SETUP_WINDOWS.md first.

1. Set $FUCHSIA_EMBEDDER_DIR to your flutter-embedder.git checkout location, for example ~/flutter-embedder.

   export FUCHSIA_EMBEDDER_DIR=$HOME/flutter-embedder
   

2. Bootstrap the repository's dependencies:

   $FUCHSIA_EMBEDDER_DIR/scripts/bootstrap.sh
   

   This script initializes tools (including bazel and ffx), installs some Git hooks and downloads the workstation_eng.qemu-x64 product bundle, which you can use to run the examples below.

Run an example app

1. Start the emulator.

   If running in a graphical environment:

   $FUCHSIA_EMBEDDER_DIR/tools/ffx emu start workstation_eng.qemu-x64
   

   If running in a terminal environment:

   $FUCHSIA_EMBEDDER_DIR/tools/ffx emu start --headless workstation_eng.qemu-x64
   

   The workflow below also supports Fuchsia builds from source that are within Fuchsia's SDK compatibility window (six weeks).

2. Set the default target in ffx to be fuchsia-emulator:

   $FUCHSIA_EMBEDDER_DIR/tools/ffx target default set fuchsia-emulator
   

3. Run an example component:

   $FUCHSIA_EMBEDDER_DIR/scripts/build_and_run_example.sh hello_flutter
   

   • To watch logs for the example component, run:

     $FUCHSIA_EMBEDDER_DIR/scripts/build_and_run_example.sh hello_flutter --log
     

     If you want to watch all logs, run $FUCHSIA_EMBEDDER_DIR/tools/ffx log in a separate terminal.

   • To watch FIDL calls for the example component, run:

     $FUCHSIA_EMBEDDER_DIR/scripts/build_and_run_example.sh hello_flutter --fidl
     

     Caveats:

     • --fidl currently requires setting $FUCHSIA_DIR to a Fuchsia source checkout with a build in $FUCHSIA_DIR/out/default. This directory is only used to read IR files for FIDL, you can still use the workstation_eng.qemu-x64 product bundle with --fidl.

     • --fidl attaches after the component has been run, so it does not pick up FIDL calls made when the component starts.

     TODO(akbiggs): Work with Bazel SDK team to get proper support for --fidl.

TODO(akbiggs): The app occasionally gets stuck on a loading screen instead of rendering. Re-running the app usually fixes it. We need to fix this.

Syncing engine artifacts

Occasionally you will need to update the Flutter Engine artifacts (embedder.h and libengine_flutter.so) that are used by the embedder to run Flutter apps. A script is provided for this workflow.

Requirements

1. You will need to get the Flutter Engine source code. Note that this is not just cloning https://github.com/flutter/engine.

2. Set $ENGINE_DIR to the src folder of your Flutter Engine checkout location, for example ~/engine/src.

3. You will need to install depot_tools and add it to your PATH.

   export PATH=$HOME/depot_tools:$PATH
   

4. For sync_engine_artifacts_to_revision.sh, you will need to git stash or git commit any local changes to the Flutter Engine. This is not necesssary for build_and_copy_engine_artifacts.sh.

Running the script

You can run the script with a flutter/engine Git commit to sync the Engine artifacts to that revision.

$FUCHSIA_EMBEDDER_DIR/scripts/sync_engine_artifacts_to_revision.sh <ENGINE_COMMIT_SHA>

A common workflow is to sync your Engine commit to the Flutter tool in this repository, for example when updating the Flutter tool to a new version. To do this:

$FUCHSIA_EMBEDDER_DIR/scripts/sync_engine_artifacts_to_revision.sh $(cat $FUCHSIA_EMBEDDER_DIR/third_party/dart-pkg/internal/flutter/flutter/bin/internal/engine.version)

If you want to test local changes to the Engine, you can run build_and_copy_engine_artifacts.sh instead, which simply builds and copies your Engine into $FUCHSIA_EMBEDDER_DIR.

$FUCHSIA_EMBEDDER_DIR/scripts/build_and_copy_engine_artifacts.sh

Uploading changes for review

flutter-embedder reviews are handled using Gerrit at https://fuchsia-review.googlesource.com, which uses a single commit per code review. See this guide for an intro to Gerrit.

An alternative Gerrit workflow is a branchless workflow where you do all your work from origin/main without creating new branches. We describe such a workflow below, but it‘s not mandatory, it’s just provided as an example.

An example branchless workflow for creating a new change is:

# Start work from an up-to-date main branch.
git fetch origin
git checkout origin/main
# Modify some files...
...
# Stage and commit your changes.
git add file1.cc file2.h
git commit -m "[embedder] My cool new feature."
# Upload for review.
git push origin HEAD:refs/for/main

An example branchless workflow to apply feedback during a code review is:

1. Visit https://fuchsia-review.googlesource.com and find your change.

2. Select ... > Download patch > Checkout and copy the command.

3. Run the following commands:

   # Start from main with your change on top.
   <paste the command you copied above>
   # Make some changes to some files to apply the feedback...
   ...
   # Stage and amend your changes to your commit.
   git add file1.cc file2.h
   git commit --amend
   # Upload your updated change for review.
   git push origin HEAD:refs/for/main
   

An example branchless workflow to create a chain of changes is:

# Start work from an up-to-date main branch.
git fetch origin
git checkout origin/main
# Modify some files...
...
# Stage and commit your changes.
git add file1.cc file2.h
git commit -m "[embedder] My cool new feature 1."
# Upload for review.
git push origin HEAD:refs/for/main
# Do some more work on top of your cool new feature.
git add file3.cc file4.h
git commit -m "[embedder] My cool new feature 2."
# Create a second code review for your second feature.
# The second code review will only show changes for
# your second feature and it will indicate that it is based on
# top of the first feature.
git push origin HEAD:refs/for/main

A branchless workflow comes with some benefits:

1. It reduces the amount of local branches you have to track.
2. It reduces the amount of local branches you have to clean up after submission.
3. It reduces the amount of overhead to starting new work (just git checkout origin/main).

However a branchless workflow also prevents you from storing multiple chains of commits locally. Uploading your changes to https://fuchsia-review.googlesource.com frequently can help address that problem, as https://fuchsia-review.googlesource.com then acts as the storage for each of your ongoing changes. This also keeps your changes in a state where they're easy to share and hand off to other people.