# Pigeon Contributor's Guide

## Description

Pigeon is a code generation tool that adds type safety to Flutter’s Platform
Channels.  This document serves as an overview of how it functions to help
people who would like to contribute to the project.

## Source Index

* [ast.dart](./lib/src/ast.dart) - The data structure for representing the Abstract Syntax Tree.
* [dart_generator.dart](./lib/src/dart/dart_generator.dart) - The Dart code generator.
* [java_generator.dart](./lib/src/java/java_generator.dart) - The Java code generator.
* [kotlin_generator.dart](./lib/src/kotlin/kotlin_generator.dart) - The Kotlin code generator.
* [objc_generator.dart](./lib/src/objc/objc_generator.dart) - The Objective-C code
  generator (header and source files).
* [swift_generator.dart](./lib/src/swift/swift_generator.dart) - The Swift code generator.
* [cpp_generator.dart](./lib/src/cpp/cpp_generator.dart) - The C++ code generator.
* [gobject_generator.dart](./lib/src/gobject/gobject_generator.dart) - The GObject code generator.
* [generator_tools.dart](./lib/src/generator_tools.dart) - Shared code between generators.
* [pigeon_cl.dart](./lib/src/pigeon_cl.dart) - The top-level function executed by
  the command line tool in [bin/][./bin].
* [pigeon_lib.dart](./lib/src/pigeon_lib.dart) - The top-level function for the
  PigeonIsolate and the AST generation code.
* [pigeon.dart](./lib/pigeon.dart) - A file of exported modules, the intended
  import for users of Pigeon.

## Testing Overview

Pigeon has 3 types of tests; you'll find them all in
[test.dart](./tool/test.dart).

* Unit tests - These are the fastest tests that are just typical unit tests,
  they may be generating code and checking it against a regular expression to
  see if it's correct.  Example:
  [dart_generator_test.dart](./test/dart_generator_test.dart)
* Compilation tests -  These tests generate code, then attempt to compile that
  code.  These are tests are much slower than unit tests, but not as slow as
  integration tests.  These tests are typically run against the Pigeon files in
  [pigeons](./pigeons).
* Integration tests - These tests generate code, then compile the generated
  code, then execute the generated code.  It can be thought of as unit-tests run
  against the generated code.  Examples: [platform_tests](./platform_tests)

For local testing, always use `test.dart` rather than `run_tests.dart`, as
`run_tests.dart` is specifically a CI entrypoint. When iterating on a specific
generator, you will likely want to use the `-t` flag to specific only the
relevant tests. Pass `-l` to get a list of available tests for the `-t` flag.

## Generated Source Code Example

This is what the temporary generated code that the _PigeonIsolate_ executes
looks like (see [State Diagram](#state-diagram)):

```dart
import 'path/to/supplied/pigeon/file.dart';
import 'dart:io';
import 'dart:isolate';
import 'package:pigeon/pigeon_lib.dart';
void main(List<String> args, SendPort sendPort) async {
  sendPort.send(await Pigeon.run(args));
}
```

This is how `dart:mirrors` gets access to the supplied Pigeon file.
