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source_gen provides:

  • A tool for generating code that is part of your Dart project.
  • A framework for creating and using multiple code generators in a single project.
  • A convention for human and tool generated Dart code to coexist with clean separation.


Given a library example.dart with an Person class annotated with @JsonSerializable:

library source_gen.example;

import 'package:source_gen/generators/json_serializable.dart';
part 'example.g.dart';

class Person extends Object with _$PersonSerializerMixin {
  final String firstName, middleName, lastName;

  final DateTime dateOfBirth;

  Person(this.firstName, this.lastName, {this.middleName, this.dateOfBirth});

  factory Person.fromJson(json) => _$PersonFromJson(json);

source_gen creates the corresponding part example.g.dart:

part of source_gen.example;

Person _$PersonFromJson(Map json) => new Person(
    json['firstName'], json['lastName'],
    middleName: json['middleName'],
    dateOfBirth: json['date-of-birth'] == null
        ? null
        : DateTime.parse(json['date-of-birth']));

abstract class _$PersonSerializerMixin {
  String get firstName;
  String get middleName;
  String get lastName;
  DateTime get dateOfBirth;
  Map<String, dynamic> toJson() => <String, dynamic>{
        'firstName': firstName,
        'middleName': middleName,
        'lastName': lastName,
        'date-of-birth': dateOfBirth?.toIso8601String(),

See the example code in the source_gen GitHub repo.

Creating a generator

Extend the Generator class to plug into source_gen.

Running generators

source_gen is based on the build package ( pub, GitHub).

See build.dart and watch.dart in the tool directory. Both reference tool/phases.dart, which contains information mapping source_gen generators to target files.

source_gen vs Dart Transformers

Dart Transformers are often used to create and modify code and assets as part of a Dart project.

Transformers allow modification of existing code and encapsulates changes by having developers use pub commands – run, serve, and build.

source_gen provides a different model. Code is generated and updated as part of a project. It is designed to create part files that augment developer maintained Dart libraries.

Generated code MAY be checked in as part of our project source, although the decision may vary depending on project needs.

Generated code SHOULD be included when publishing a project as a pub package. The fact that source_gen is used in a package is an implementation detail.







This is kept as a separate library from the generator intentionally to minimize transitive dependencies of types that are annotated as serializable.