Daco Harkes 1f16d9121c
[native_assets] Add support for link hooks (#148474)
This PR adds support invoking `link.dart` hooks.

Link hooks can add new assets. Link hooks can transform assets sent to link hook from build hooks.

This PR does not yet add support for getting tree-shake information in the link hooks. This is pending on defining the `resources.json` format (https://github.com/dart-lang/sdk/issues/55494).

Issue:

* https://github.com/flutter/flutter/issues/146263

## Implementation considerations

The build hooks could be run before Dart compilation and the link hooks after Dart compilation. (This is how it's done in Dart standalone.) However, due to the way the `Target`s are set up, this would require two targets and serializing and deserializing the `BuildResult` in between these. This would lead to more code but no benefits. Currently there is nothing that mandates running build hooks before Dart compilation.

## Testing

* The unit tests verify that the native_assets_builder `link` and `linkDryRun` would be invoked with help of the existing fake.
* The native assets integration test now also invokes an FFI call of a package that adds the asset during the link hook instead of the build hook.
  * In order to keep coverage of the `flutter create --template=package_ffi`, `flutter create` is still run and the extra dependency is added and an extra ffi call is added. (Open to alternative suggestions.)
2024-05-22 16:02:00 +00:00
..
2024-01-12 22:10:25 +00:00

# {{projectName}}

{{description}}

## Getting Started

This project is a starting point for a Flutter
[FFI package](https://docs.flutter.dev/development/platform-integration/c-interop),
a specialized package that includes native code directly invoked with Dart FFI.

## Project structure

This template uses the following structure:

* `src`: Contains the native source code, and a CmakeFile.txt file for building
  that source code into a dynamic library.

* `lib`: Contains the Dart code that defines the API of the plugin, and which
  calls into the native code using `dart:ffi`.

* `bin`: Contains the `build.dart` that performs the external native builds.

## Building and bundling native code

`build.dart` does the building of native components.

Bundling is done by Flutter based on the output from `build.dart`.

## Binding to native code

To use the native code, bindings in Dart are needed.
To avoid writing these by hand, they are generated from the header file
(`src/{{projectName}}.h`) by `package:ffigen`.
Regenerate the bindings by running `dart run ffigen --config ffigen.yaml`.

## Invoking native code

Very short-running native functions can be directly invoked from any isolate.
For example, see `sum` in `lib/{{projectName}}.dart`.

Longer-running functions should be invoked on a helper isolate to avoid
dropping frames in Flutter applications.
For example, see `sumAsync` in `lib/{{projectName}}.dart`.

## Flutter help

For help getting started with Flutter, view our
[online documentation](https://flutter.dev/docs), which offers tutorials,
samples, guidance on mobile development, and a full API reference.