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

packages/dart_mappable/doc/configuration.md

@@ -81,6 +81,26 @@ global_options:
       generateMethods: [decode, encode, copy, stringify, equals]
 ```
 
+### `build_extensions`
+
+The `build_extensions` option allows you to specify custom paths for the generated files. This is particularly useful when working with certain code generation scenarios. It takes a map where keys are paths to source files and values are lists of corresponding generated file paths.
+
+#### Example:
+
+Here is an example to write in a build.yaml file to generate the generated files in a `generated` folder:
+```yaml
+targets:
+  $default:
+    builders:
+      # only to resolve build_runner conflicts
+      dart_mappable_builder:
+        options:
+          build_extensions:
+            'lib/{{path}}/{{file}}.dart':
+              - 'lib/{{path}}/generated/{{file}}.mapper.dart'
+              - 'lib/{{path}}/generated/{{file}}.init.dart'
+```
+
 ---
 
 <p align="right"><a href="../topics/Copy-With-topic.html">Next: Copy-With</a></p>

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 +93,20 @@ class MappableBuilder implements Builder {
 
     var output = await Future.wait(generators.map((g) => g.generate()));
 
+    final outputId = buildStep.allowedOutputs.first;
+
+    var libraryPath =
+        p.relative(buildStep.inputId.path, from: p.dirname(outputId.path));
     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 \'${p.basename(buildStep.inputId.uri.toString())}\';\n\n'
+        'part of \'$libraryPath\';\n\n'
         '${output.join('\n\n')}\n' //,
         );
-    var outputId = buildStep.inputId.changeExtension('.mapper.dart');
+
     await buildStep.writeAsString(outputId, source);
   }
 
@@ -123,9 +125,12 @@ class MappableBuilder implements Builder {
 
     discovered.sortBy((e) => e.key.source.uri.toString());
 
+    final outputId = buildStep.allowedOutputs.last;
+
     output.write(writeImports(
       buildStep.inputId,
       discovered.map((e) => e.key.source.uri).toList(),
+      p.dirname(outputId.uri.path),
     ));
 
     output.write('void initializeMappers() {\n');
@@ -146,12 +151,11 @@ class MappableBuilder implements Builder {
       '${output.toString()}\n',
     );
 
-    var outputId = buildStep.inputId.changeExtension('.init.dart');
     await buildStep.writeAsString(outputId, source);
   }
 }
 
-String writeImports(AssetId input, List<Uri> imports) {
+String writeImports(AssetId input, List<Uri> imports, String outputDirectory) {
   List<String> package = [], relative = [];
   var prefixes = <String, int?>{};
 
@@ -160,21 +164,14 @@ String writeImports(AssetId input, List<Uri> imports) {
   for (var i = 0; i < imports.length; i++) {
     var import = imports[i];
     if (import.isScheme('asset')) {
-      var relativePath =
-          path.relative(import.path, from: path.dirname(input.uri.path));
+      var relativePath = path.relative(import.path, from: outputDirectory);
 
       relative.add(relativePath);
       prefixes[relativePath] = i;
     } else if (import.isScheme('package') &&
         import.pathSegments.first == input.package &&
         input.pathSegments.first == 'lib') {
-      var libPath =
-          import.replace(pathSegments: import.pathSegments.skip(1)).path;
-
-      var inputPath =
-          input.uri.replace(pathSegments: input.uri.pathSegments.skip(1)).path;
-
-      var relativePath = path.relative(libPath, from: path.dirname(inputPath));
+      var relativePath = path.relative(import.path, from: outputDirectory);
 
       relative.add(relativePath);
       prefixes[relativePath] = i;

packages/dart_mappable_builder/lib/src/utils.dart

@@ -165,3 +165,52 @@ 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;
+}