sdk/pkg/analysis_server_plugin/doc/writing_a_plugin.md

Writing a plugin

This document describes how to write an analyzer plugin, to provide custom static analysis, or to offer custom quick fixes in an IDE.

The pubspec file

An analyzer plugin is a Dart package, so let's start with the pubspec.yaml file:

name: test_analyzer_plugin
version: 0.0.1

environment:
  sdk: '>=3.6.0 <4.0.0'

dependencies:
  analysis_server_plugin: any
  analyzer: ^7.2.0

There is nothing special about this pubspec; note that we need a dependency on the analysis_server_plugin package, and on the analyzer package, supporting at least 7.2.0. The version of the analyzer package needs to move lockstep with the Dart SDK. For Dart 3.8.0-70.1.beta, ^7.2.0 is a good version constraint.

The main Dart file

One source file is required, at lib/main.dart. Here is the basic layout:

import 'package:analysis_server_plugin/plugin.dart';
import 'package:analysis_server_plugin/registry.dart';

final plugin = SimplePlugin();

class SimplePlugin extends Plugin {
  @override
  void register(PluginRegistry registry) {
    // Here we register analysis rules, and quick fixes.
  }
}

Here we have a class, SimplePlugin, which extends the Plugin class from the analysis_server_plugin package. This class has one method that we override: register. In the register method, we can register analysis rules and quick fixes (CorrectionProducers). See details in the writing rules doc, and the writing fixes doc.

Additionally, we provide a top-level variable in this file called plugin, which is an instance of our SimplePlugin class. When a running instance of the Dart Analysis Server needs to use this analyzer plugin, it generates some code that needs to import this lib/main.dart file, and that references this plugin top-level variable.

Debugging a plugin

If a plugin is not behaving as expected (for example, warnings are not appearing in the IDE), you can check the analyzer diagnostics pages. If the plugin isolate has crashed, the "plugins" screen will display the crash.

print cannot be used in plugin code to debug. Instead, writing to a log file can help in debugging plugin code.