When using an aggregate builder, I notice that the generate_for option on the TargetBuilderConfig in the build.yaml changes behaviour. The builder will only output if the target builder is set to default where as for normal builders setting the generate_for does work as expected.

This is my folder structure

lib
- entity_a.dart
- entity_b.dart
protos

where using the default generate_for of ** seems to work and outputs one proto file with aggregated content in the protos folder. But upon setting the generate_for to lib/**.dart it will stop outputting the proto file. But why?

This is my target build.yaml

targets:
  $default:
    builders:
      package_name|builder_name:
        enabled: true
        generate_for:
          - lib/**.dart

Which only works when removing the generate_for. And this is my build.yaml in my generator package.

builders:
  builder_name:
    import: "package:package_name/builders.dart"
    builder_factories: ["build"]
    build_extensions: {'$package$': ['protos/model.proto']}
    build_to: source
    auto_apply: root_package

And this is my builder

import 'package:build/build.dart';
import 'package:glob/glob.dart';

Builder build(BuilderOptions options) => ProtoBuilder();

class ProtoBuilder implements Builder {
  static final _allFilesInLib = Glob('**.dart');

  static AssetId _allDartFiles(BuildStep buildStep) {
    return AssetId(
      buildStep.inputId.package,
      'protos/model.proto',
    );
  }

  @override
  Map<String, List<String>> get buildExtensions {
    return const {
      r'$package$': ['protos/model.proto'],
    };
  }

  @override
  Future<void> build(BuildStep buildStep) async {
    final files = <String>[];
    await for (final input in buildStep.findAssets(_allFilesInLib)) {
      files.add(input.path);
    }
    final output = _allDartFiles(buildStep);
    return buildStep.writeAsString(output, files.join('n'));
  }
}