add the possibility to set a build_extensions option in the build.yaml

packages/dart_mappable_builder/lib/src/builder_options.dart

@@ -3,6 +3,10 @@ import 'package:dart_mappable/dart_mappable.dart';
 
 import 'utils.dart';
 
+const _defaultExtensions = {
+  '.dart': ['.mapper.dart', '.init.dart']
+};
+
 /// The builder options for a specific library
 class MappableOptions {
   final CaseStyle? caseStyle;
@@ -13,6 +17,7 @@ class MappableOptions {
   final InitializerScope? initializerScope;
   final int? lineLength;
   final Map<String, String> renameMethods;
+  final Map<String, List<String>> buildExtensions;
 
   MappableOptions({
     this.caseStyle,
@@ -23,6 +28,7 @@ class MappableOptions {
     this.initializerScope,
     this.lineLength,
     this.renameMethods = const {},
+    this.buildExtensions = _defaultExtensions,
   });
 
   MappableOptions.parse(Map options)
@@ -36,7 +42,9 @@ class MappableOptions {
         initializerScope = null,
         lineLength =
             options['lineLength'] as int? ?? options['line_length'] as int?,
-        renameMethods = toMap(options['renameMethods'] ?? {});
+        renameMethods = toMap(options['renameMethods'] ?? {}),
+        buildExtensions =
+            validatedBuildExtensionsFrom(options, _defaultExtensions);
 
   MappableOptions apply(MappableOptions? options, {bool forceJoin = true}) {
     if (options == null) return this;

packages/dart_mappable_builder/lib/src/builders/mappable_builder.dart

@@ -50,9 +50,7 @@ class MappableBuilder implements Builder {
   }
 
   @override
-  Map<String, List<String>> get buildExtensions => const {
-        '.dart': ['.mapper.dart', '.init.dart']
-      };
+  Map<String, List<String>> get buildExtensions => options.buildExtensions;
 
   Future<MapperElementGroup> createMapperGroup(BuildStep buildStep) async {
     var entryLib = await buildStep.inputLibrary;
@@ -95,16 +93,17 @@ class MappableBuilder implements Builder {
 
     var output = await Future.wait(generators.map((g) => g.generate()));
 
+    final outputId = buildStep.allowedOutputs.first;
     var source = DartFormatter(pageWidth: options.lineLength ?? 80).format(
         '// coverage:ignore-file\n'
         '// GENERATED CODE - DO NOT MODIFY BY HAND\n'
         '// ignore_for_file: type=lint\n'
         '// ignore_for_file: unused_element, unnecessary_cast\n'
         '// ignore_for_file: strict_raw_type, inference_failure_on_untyped_parameter\n\n'
-        'part of \'${p.basename(buildStep.inputId.uri.toString())}\';\n\n'
+        'part of \'${uriOfPartial(buildStep.inputId, outputId)}\';\n\n'
         '${output.join('\n\n')}\n' //,
         );
-    var outputId = buildStep.inputId.changeExtension('.mapper.dart');
+
     await buildStep.writeAsString(outputId, source);
   }
 
@@ -138,6 +137,7 @@ class MappableBuilder implements Builder {
 
     output.write('}');
 
+    final outputId = buildStep.allowedOutputs.last;
     var source = DartFormatter(pageWidth: options.lineLength ?? 80).format(
       '// coverage:ignore-file\n'
       '// GENERATED CODE - DO NOT MODIFY BY HAND\n'
@@ -146,7 +146,6 @@ class MappableBuilder implements Builder {
       '${output.toString()}\n',
     );
 
-    var outputId = buildStep.inputId.changeExtension('.init.dart');
     await buildStep.writeAsString(outputId, source);
   }
 }

packages/dart_mappable_builder/lib/src/utils.dart

@@ -165,3 +165,82 @@ extension ObjectReader on DartObject {
     return result;
   }
 }
+
+Map<String, List<String>> validatedBuildExtensionsFrom(
+  Map? optionsMap,
+  Map<String, List<String>> defaultExtensions,
+) {
+  final extensionsOption = optionsMap?.remove('build_extensions');
+  if (extensionsOption == null) {
+    // defaultExtensions are provided by the builder author, not the end user.
+    // It should be safe to skip validation.
+    return defaultExtensions;
+  }
+
+  if (extensionsOption is! Map) {
+    throw ArgumentError(
+      'Configured build_extensions should be a map from inputs to outputs.',
+    );
+  }
+
+  final result = <String, List<String>>{};
+
+  for (final entry in extensionsOption.entries) {
+    final input = entry.key;
+    if (input is! String || !input.endsWith('.dart')) {
+      throw ArgumentError(
+        'Invalid key in build_extensions option: `$input` '
+        'should be a string ending with `.dart`',
+      );
+    }
+
+    final output = (entry.value is List) ? entry.value as List : [entry.value];
+
+    for (var i = 0; i < output.length; i++) {
+      final o = output[i];
+      if (o is! String || (i == 0 && !o.endsWith('.dart'))) {
+        throw ArgumentError(
+          'Invalid output extension `${entry.value}`. It should be a string '
+          'or a list of strings with the first ending with `.dart`',
+        );
+      }
+    }
+
+    result[input] = output.cast<String>().toList();
+  }
+
+  if (result.isEmpty) {
+    throw ArgumentError('Configured build_extensions must not be empty.');
+  }
+  return result;
+}
+
+String uriOfPartial(AssetId source, AssetId output) {
+  assert(source.package == output.package);
+  String sourcePath = source.path;
+  String outputPath = output.path;
+
+  // Split the paths into individual segments.
+  List<String> sourceSegments = sourcePath.split('/');
+  List<String> outputSegments = outputPath.split('/');
+
+  // Find the common prefix between source and output paths.
+  int commonIndex = 0;
+  for (int i = 0; i < sourceSegments.length && i < outputSegments.length; i++) {
+    if (sourceSegments[i] != outputSegments[i]) {
+      break;
+    }
+    commonIndex = i;
+  }
+
+  // Calculate the relative path.
+  List<String> relativeSegments = List.generate(
+    outputSegments.length - commonIndex - 2,
+    (_) => '..',
+  );
+  relativeSegments.addAll(sourceSegments.sublist(commonIndex + 1));
+
+  // Join the segments to form the relative path.
+  String relativePath = relativeSegments.join('/');
+  return relativePath;
+}

packages/dart_mappable_builder/test/simple_model_test.dart

@@ -1,3 +1,5 @@
+import 'package:build/build.dart';
+import 'package:dart_mappable_builder/src/utils.dart';
 import 'package:test/test.dart';
 
 import 'utils/test_mappable.dart';
@@ -31,5 +33,14 @@ void main() {
         },
       );
     });
+
+    test('uriOfPartial', () {
+      AssetId input = AssetId('package', 'lib/models/model.dart');
+      AssetId output = AssetId('package',
+          'lib/models/subfolder1/subfolder2/subfolder3/model.mapper.dart');
+      expect(uriOfPartial(input, output), '../../../model.dart');
+      expect(uriOfPartial(output, input),
+          'subfolder1/subfolder2/subfolder3/model.mapper.dart');
+    });
   });
 }