The build_itis a builder that makes publicly available third-party source code generators and runs them during the build process for rapid development.

Version 0.2.8 (BETA)


  • Add the development build_it JSON generator (build_it:json_dev) that will generate a file with the .dart extension with JSON classes (generated by json_serializable) without the part and part of directives (and without the files with extensions .g.dart). This will be done by combining the parts into one file. This generator allows you to create JSON classes that will not be deleted during build process and will always be available.

What are the benefits of using?

The build_it builder simplifies several development steps at once:

  • Source code generators are given full (and simplified) access to build steps: build and post build
  • Allows you to easily use your own generator without delving too much into the principles of the build process (generate whatever you want)
  • You can use your own data description format to configure your generator in YAML format (it is recommended to use JSON models for this purpose)
  • You can use third-party source code generators for rapid development, you just need to know the configuration description format (and what they end up creating)
  • Includes built-in build_it:json JSON generator maximum compatible with package json_serializable and its annotations
  • A built-in JSON generator is provided to simplify the creation of generators specification models, or it can be used to generate code for JSON classes that are commonly used

What are the principles of work?

The build_it builder is a common builder for the Dart build system. It is intended for building Dart projects.
It is configured and for those who use it there is no need to worry about how it works.
On the other hand, it allows you to use third-party (or your own) code generators quite simply without the need to know how it all works.
If you need to generate code based on some configuration, then you simply create a configuration file for a specific generator and build_it builder does all the work for you (runs the corresponding generator).

How do generators become publicly available?

Create a file named your_generator_name_build_it.dart.
That is, add _build_it.dart at the end of the generator file name.
Your generator will be available to anyone who adds dependencies to your package.
The generator will be available with the name your_package_name:generator_name.
Or, if your generator has the same name as your package, then its alias (the short name) will be your_package_name.

If necessary, you can hide it away in your package.
Eg. src/foo/bar/baz_build_it.dart

File format

Input configuration files must be in the build_it format.
This is a non-existent format (don't try to find a description). This format is only intended to be able to identify data in this format.
This format is very simple. The data format is YAML.
You just need to specify the correct YAML metadata section in a certain way.

The header format (YAML metadata section) is shown below.

  name: build_it
    name: string
    version: string?

# Configuration goes here

How to use

The build_it builder directly executes third-party (or your own) generators for you.
The builder executes thеse generators that generates ready-to-use source code (or source code for other builders or generators).
The configurations for generators are described in the YAML format.
Configurations are based on specifications.
That is, you describe the configuration in the YAML format according to the specification. Because the target generator will use this configuration for its work.

How to implement your own build_it generator?

First, add a dependency to the pubspec.yaml file:

  json_annotation: ^4.0.0
  build_it: ^0.2.3
  json_serializable: ^4.0.2 

Suppose you want to create a generator named example.

Create a file named example_build_it.dart in thelib folder.

Add the following directive (for data exchange with the builder):

import 'package:build_it/build_it_models.dart';

Create a main method:

Future<void> main(List<String> args, [response]) async {

And add some code to it.

import 'package:build_it/build_it_helper.dart';
import 'package:json_helpers/json_helpers.dart';

Future<void> main(List<String> args, [message]) async {
  return await buildIt(args, message, _build);

Future<BuildResult> _build(BuildConfig config) async {
  const _template = '''
void main() {
  stdout.writeln('Hello, {{NAME}}');

  final data = => Data.fromMap(e));
  final name =;
  final code = <String>[];
  final template = _template.replaceAll('{{NAME}}', name);
  final directives = <Directive>[];
  directives.add(Directive(type: 'import', url: 'dart:io'));
  return BuildResult(code: code.join('\n'), directives: directives);

class Data {
  final String name;


  factory Data.fromMap(Map<String, dynamic> json) {
    return Data(name: (json['name'] as String?) ?? '');


Then create your config file:


  name: build_it
    name: build_it_test:example

name: Jack

We will assume that your package is named build_it_test.
Accordingly, the public available name of your generator is build_it_test:example.

Everything is ready, you can start the build process:

dart run build_runner build

Below is the build (and generation) result:



import 'dart:io';

// **************************************************************************
// build_it: build_it_test:example
// **************************************************************************

void main() {
  stdout.writeln('Hello, Jack');

Yes, it’s not impressive, but we didn't put much effort into it.
It is best to use the package code_builder.
Another way is to use a template engine (for example, mustache).

A good generator should have a format specification and use JSON models to work with the configuration.
Package build_it offers a built-in JSON generator. This generator will be improved soon. You can use it to generate JSON models for your generator.

Built-in JSON generator

For a generator to work well, a specification is required to describe the configuration and to work with the configuration.
JSON classes are very well suited for this purpose. They are convenient for modeling and data processing.
It is not very pleasant to write such classes by hand, it is a common routine work.
Using the json generator from thebuild_it package can make this work a little easier.

Example of configuration for JSON generator:


  name: build_it
    name: build_it:json

checkNullSafety: true
  anyMap: true

- name: Category
  - { name: id, type: int? }
  - { name: name, type: String? }
  - { name: products, type: List<Product>, jsonKey: { defaultValue: [] } }

- name: Product
  - { name: id, type: int? }
  - { name: name, type: String? }
  - { name: type, type: ProductType, jsonKey: { defaultValue: ProductType.product } }

- name: ProductType
  - { name: product, jsonValue: { value: 0 } }
  - { name: service, jsonValue: { value: 1 } }

code: |
  int _foo(String s) {
    return 41;

The result of work:



import 'package:json_annotation/json_annotation.dart';

part 'example_classes.g.g.dart';

// **************************************************************************
// build_it: build_it:json
// **************************************************************************

@JsonSerializable(anyMap: true)
class Category {
  Category({,, required this.products});

  /// Creates an instance of 'Category' from a JSON representation
  factory Category.fromJson(Map json) => _$CategoryFromJson(json);

  int? id;

  String? name;

  @JsonKey(defaultValue: [])
  List<Product> products;

  /// Returns a JSON representation of the 'Category' instance.
  Map<String, dynamic> toJson() => _$CategoryToJson(this);

@JsonSerializable(anyMap: true)
class Product {
  Product({,, required this.type});

  /// Creates an instance of 'Product' from a JSON representation
  factory Product.fromJson(Map json) => _$ProductFromJson(json);

  int? id;

  String? name;

  @JsonKey(defaultValue: ProductType.product)
  ProductType type;

  /// Returns a JSON representation of the 'Product' instance.
  Map<String, dynamic> toJson() => _$ProductToJson(this);

enum ProductType {

int _foo(String s) {
  return 41;

This generator is an example of how and what kind of public generators can be written and used with the build_it builder.
If you add the following dependencies to your project, then this generator will be available in your project as well.

  json_annotation: ^4.0.0
  build_it: ^0.2.3
  json_serializable: ^4.0.2

Now everyone who adds dependencies will have access to this generator.

This way everyone can easily create useful public generators for everyone.
This applies to all generators intended to use with build_it builder.

How to avoid bulld conflicts?

The only way to avoid build conflicts is to not create a Dart file with the same name as the configuration file.
For example, if you are using a configuration file named my_models.yaml, then do not create a file called my_models.dart.
The reason for the possible conflict may be that if the file my_models.dart will generate the filemy_models.g.dart, then there will be a build conflict.

How to debug generator?

If you need to debug the process of work 'build_it', then you can read the answer here: can I debug my builder?)

But if you need to debug your code generator, then it is easier to do so:
Move the generator functionality into a separate class and debug it in the usual way.
The builder 'build_it' runs the generator in a separate isolate, this debugging is not very convenient.

To be continued...