build_runner

https://pub.dev/documentation/build_runner/latest
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build_runner is a code generation system for Dart and Flutter that enables automatic code generation...
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### Example Dart DevTools output

Source: https://pub.dev/documentation/build_runner/latest

Displays the URL provided by the build process for connecting the Dart DevTools debugger.

```text
The Dart DevTools debugger and profiler is available at:
http://127.0.0.1:8181/3xXtAPE8msc=/devtools/?uri=ws://127.0.0.1:8181/3xXtAPE8msc=/ws
```

--------------------------------

### Update class with new fields

Source: https://pub.dev/documentation/build_runner/latest

Example of updating a class definition that triggers the watch mode to regenerate code.

```dart
@JsonSerializable()
class Person {
  final String name;
  final DateTime? dateOfBirth;
  // Added.
  final int age;

  // Updated manually.
  Person({required this.name, this.dateOfBirth, this.age});

  // No change needed, the generated implementations referenced get updated.
  Map<String, dynamic> toJson() => _$PersonToJson(this);
  factory Person.fromJson(Map<String, dynamic> json) => _$PersonFromJson(json);
}
```

--------------------------------

### Run build_runner commands

Source: https://pub.dev/documentation/build_runner/latest

Execute build or watch commands from the terminal in the package root.

```bash
cd <package root folder>
dart run build_runner build
```

```bash
cd <package root folder>
dart run build_runner watch
```

--------------------------------

### Configure pubspec.yaml for json_serializable

Source: https://pub.dev/documentation/build_runner/latest

Add the necessary dependencies and dev_dependencies to your pubspec.yaml file.

```yaml
dependencies:
  json_annotation: ^4.9.0

dev_dependencies:
  build_runner: ^2.6.0
  json_serializable: ^6.10.0
```

--------------------------------

### Configure builder options in build.yaml

Source: https://pub.dev/documentation/build_runner/latest

Set specific options for builders like freezed.

```yaml
targets:
  $default:
    builders:
      freezed:
        options:
          # Do format output.
          format: true
          # Don't generate `copyWith` or `operator==`.
          copy_with: false
          equal: false
```

--------------------------------

### Debug build_runner with Dart VM arguments

Source: https://pub.dev/documentation/build_runner/latest

Passes debugging arguments to the child process spawned by build_runner to enable observation and isolate pausing.

```bash
dart run build_runner build --dart-jit-vm-arg=--observe --dart-jit-vm-arg=--pause-isolates-on-start
```

--------------------------------

### Configure build.yaml for target restrictions

Source: https://pub.dev/documentation/build_runner/latest

Restrict which files a builder processes using the generate_for option.

```yaml
targets:
  $default:
    builders:
      json_serializable:
        generate_for:
          # Only run `json_serializable` on source under `lib/models`.
          - lib/models/*.dart
```

--------------------------------

### Ignore .dart_tool in .gitignore

Source: https://pub.dev/documentation/build_runner/latest

Add the internal build_runner directory to your .gitignore file.

```text
.dart_tool
```

--------------------------------

### Activate json_serializable in a Dart class

Source: https://pub.dev/documentation/build_runner/latest

Use the @JsonSerializable annotation and part directive to enable code generation for a class.

```dart
import 'package:json_annotation/json_annotation.dart';

// Include the file that the builder will generate.
part 'example.g.dart';.

// Activate the builder.
@JsonSerializable()
class Person {
  final String name;
  final DateTime? dateOfBirth;

  Person({required this.name, this.dateOfBirth});

  // Wire up the generated `toJson` in `example.g.dart`.
  Map<String, dynamic> toJson() => _$PersonToJson(this);

  // Wire up the generated `fromJson` in `example.g.dart`.
  factory Person.fromJson(Map<String, dynamic> json) => _$PersonFromJson(json);
}
```
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