Add --packages flag to dart run in arcade serve for Dart 3.10 compatibility

packages/arcade_cli/lib/commands/serve.dart

@@ -14,11 +14,23 @@ class ServeCommand extends Command {
   @override
   String get description => 'Locally serve your app';
 
+  /// Builds the dart run arguments, including --packages flag if package
+  /// config is found.
+  List<String> _buildDartRunArgs(String serverPath, String? packageConfig) {
+    final runArgs = ['run', '-r'];
+    if (packageConfig != null) {
+      runArgs.addAll(['--packages=$packageConfig']);
+    }
+    runArgs.add(serverPath);
+    return runArgs;
+  }
+
   @override
   Future<void> run() async {
     Process? process;
     final serverFile = await getServerFile();
     final cwd = Directory.current.path;
+    final packageConfig = findPackageConfig();
 
     bool shouldReload(WatchEvent event) {
       return path.isWithin(path.join(cwd, 'bin'), event.path) ||
@@ -29,7 +41,7 @@ class ServeCommand extends Command {
 
     process = await Process.start(
       'dart',
-      ['run', '-r', serverFile.path],
+      _buildDartRunArgs(serverFile.path, packageConfig),
       workingDirectory: cwd,
     );
 
@@ -55,9 +67,10 @@ class ServeCommand extends Command {
             process?.kill();
             process = null;
             final now = DateTime.now();
+
             process = await Process.start(
               'dart',
-              ['run', '-r', serverFile.path],
+              _buildDartRunArgs(serverFile.path, packageConfig),
               workingDirectory: cwd,
             );
             stdoutSubscription = process!.stdout.listen((event) {

packages/arcade_cli/lib/utils.dart

@@ -32,3 +32,35 @@ Future<File> getServerFile() async {
   }
   return file;
 }
+
+/// Finds the package_config.json file by recursively searching parent
+/// directories. This supports Dart workspaces where the package_config.json
+/// may be in a parent directory.
+///
+/// Returns the path to the package_config.json file, or null if not found.
+String? findPackageConfig([String? startDir]) {
+  var dir = Directory(startDir ?? Directory.current.path);
+
+  // Search up to the root directory
+  while (true) {
+    final packageConfigPath = join(
+      dir.path,
+      '.dart_tool',
+      'package_config.json',
+    );
+    final packageConfigFile = File(packageConfigPath);
+
+    if (packageConfigFile.existsSync()) {
+      return packageConfigPath;
+    }
+
+    // Check if we've reached the root directory
+    final parent = dir.parent;
+    if (parent.path == dir.path) {
+      // We've reached the root
+      return null;
+    }
+
+    dir = parent;
+  }
+}

packages/arcade_cli/test/utils_test.dart

@@ -0,0 +1,81 @@
+import 'dart:io';
+
+import 'package:arcade_cli/utils.dart';
+import 'package:path/path.dart' as path;
+import 'package:test/test.dart';
+
+void main() {
+  group('findPackageConfig', () {
+    late Directory tempDir;
+    late Directory subDir;
+
+    setUp(() {
+      // Create a temporary directory structure for testing
+      tempDir = Directory.systemTemp.createTempSync('package_config_test');
+      subDir = Directory(path.join(tempDir.path, 'subdir'))..createSync();
+    });
+
+    tearDown(() {
+      // Clean up temporary directory
+      if (tempDir.existsSync()) {
+        tempDir.deleteSync(recursive: true);
+      }
+    });
+
+    test('should find package_config.json in current directory', () {
+      final dartToolDir = Directory(path.join(tempDir.path, '.dart_tool'))
+        ..createSync();
+      final packageConfigFile = File(
+        path.join(dartToolDir.path, 'package_config.json'),
+      )..createSync();
+
+      final result = findPackageConfig(tempDir.path);
+
+      expect(result, equals(packageConfigFile.path));
+    });
+
+    test('should find package_config.json in parent directory', () {
+      final dartToolDir = Directory(path.join(tempDir.path, '.dart_tool'))
+        ..createSync();
+      final packageConfigFile = File(
+        path.join(dartToolDir.path, 'package_config.json'),
+      )..createSync();
+
+      final result = findPackageConfig(subDir.path);
+
+      expect(result, equals(packageConfigFile.path));
+    });
+
+    test('should return null if package_config.json not found', () {
+      final result = findPackageConfig(tempDir.path);
+
+      expect(result, isNull);
+    });
+
+    test('should search recursively up to root', () {
+      final deepDir = Directory(
+        path.join(tempDir.path, 'a', 'b', 'c'),
+      )..createSync(recursive: true);
+
+      final dartToolDir = Directory(path.join(tempDir.path, '.dart_tool'))
+        ..createSync();
+      final packageConfigFile = File(
+        path.join(dartToolDir.path, 'package_config.json'),
+      )..createSync();
+
+      final result = findPackageConfig(deepDir.path);
+
+      expect(result, equals(packageConfigFile.path));
+    });
+
+    test('should use current directory when no start dir provided', () {
+      // This test verifies that findPackageConfig works with no arguments
+      // It should find the actual package_config.json in the project
+      final result = findPackageConfig();
+
+      // The result should be non-null for a valid Dart project
+      expect(result, isNotNull);
+      expect(result, endsWith('package_config.json'));
+    });
+  });
+}