feat: Init command

packages/melos/lib/src/command_runner.dart

@@ -13,6 +13,7 @@ import 'command_runner/bootstrap.dart';
 import 'command_runner/clean.dart';
 import 'command_runner/exec.dart';
 import 'command_runner/format.dart';
+import 'command_runner/init.dart';
 import 'command_runner/list.dart';
 import 'command_runner/publish.dart';
 import 'command_runner/run.dart';
@@ -38,7 +39,8 @@ class MelosCommandRunner extends CommandRunner<void> {
       : super(
           'melos',
           'A CLI tool for managing Dart & Flutter projects with multiple '
-              'packages.',
+              'packages.\n\n'
+              'To get started with Melos, run "melos init".',
           usageLineLength: terminalWidth,
         ) {
     argParser.addFlag(
@@ -55,6 +57,7 @@ class MelosCommandRunner extends CommandRunner<void> {
           'the special value "auto".',
     );
 
+    addCommand(InitCommand(config));
     addCommand(ExecCommand(config));
     addCommand(BootstrapCommand(config));
     addCommand(CleanCommand(config));
@@ -154,6 +157,7 @@ Future<MelosWorkspaceConfig> _resolveConfig(
 }
 
 bool _shouldUseEmptyConfig(List<String> arguments) {
+  if (arguments.firstOrNull == 'init') return true;
   final willShowHelp = arguments.isEmpty ||
       arguments.contains('--help') ||
       arguments.contains('-h');

packages/melos/lib/src/command_runner/init.dart

@@ -0,0 +1,71 @@
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+
+import '../../melos.dart';
+import '../common/utils.dart';
+import 'base.dart';
+
+class InitCommand extends MelosCommand {
+  InitCommand(super.config) {
+    argParser.addOption(
+      'directory',
+      abbr: 'd',
+      help: 'Directory to create project in. Defaults to the workspace name.',
+    );
+
+    argParser.addMultiOption(
+      'packages',
+      abbr: 'p',
+      help: 'Comma separated glob paths to add to the melos workspace.',
+    );
+
+    argParser.addOption(
+      'project',
+      abbr: 'P',
+      help: 'Project name to be used in pubspec.yaml. '
+          'Defaults to the workspace name.',
+    );
+  }
+
+  @override
+  final String name = 'init';
+
+  @override
+  final String description = 'Initialize a new Melos workspace.';
+
+  @override
+  Future<void> run() {
+    final workspaceDefault = p.basename(Directory.current.absolute.path);
+    final workspaceName = argResults!.rest.firstOrNull ??
+        promptInput(
+          'Enter your workspace name',
+          defaultsTo: workspaceDefault,
+        );
+    final directory = argResults!['directory'] as String? ??
+        promptInput(
+          'Enter the directory',
+          defaultsTo: workspaceDefault != workspaceName ? workspaceName : '.',
+        );
+    final packages = argResults!['packages'] as List<String>?;
+    final project = argResults!['project'] as String? ??
+        promptInput(
+          'Enter the project name',
+          defaultsTo: workspaceName,
+        );
+    final useAppsDir = promptBool(
+      message: 'Do you want to add the apps directory to the list of packages?',
+      defaultsTo: true,
+    );
+
+    final melos = Melos(logger: logger, config: config);
+
+    return melos.init(
+      workspaceName,
+      directory: directory,
+      packages: packages ?? const [],
+      project: project,
+      useAppDir: useAppsDir,
+    );
+  }
+}

packages/melos/lib/src/commands/init.dart

@@ -0,0 +1,63 @@
+part of 'runner.dart';
+
+mixin _InitMixin on _Melos {
+  Future<void> init(
+    String workspaceName, {
+    required String directory,
+    required List<String> packages,
+    required String project,
+    bool useAppDir = false,
+  }) async {
+    late final String qualifiedWorkspaceName;
+    if (workspaceName == '.') {
+      qualifiedWorkspaceName = p.basename(Directory.current.absolute.path);
+    } else {
+      qualifiedWorkspaceName = workspaceName;
+    }
+
+    final isCurrentDir = directory == '.';
+    final dir = Directory(directory);
+    if (!isCurrentDir && dir.existsSync()) {
+      throw StateError('Directory $directory already exists');
+    } else if (!isCurrentDir) {
+      dir.createSync(recursive: true);
+      Directory(p.join(dir.absolute.path, 'packages')).createSync();
+      if (useAppDir) {
+        Directory(p.join(dir.absolute.path, 'apps')).createSync();
+      }
+    }
+
+    final dartVersion = utils.currentDartVersion('dart');
+    final melosYaml = <String, Object?>{
+      'name': qualifiedWorkspaceName,
+      'packages': [if (useAppDir) 'apps/*', 'packages/*'],
+      if (packages.isNotEmpty) 'packages': packages,
+    };
+    final pubspecYaml = <String, dynamic>{
+      'name': project,
+      'environment': {
+        'sdk': '>=$dartVersion <${dartVersion.major + 1}.0.0',
+      },
+      'dev_dependencies': {
+        'melos': '^$melosVersion',
+      },
+    };
+
+    final melosFile = File(p.join(dir.absolute.path, 'melos.yaml'));
+    final pubspecFile = File(p.join(dir.absolute.path, 'pubspec.yaml'));
+
+    melosFile.writeAsStringSync(
+      (YamlEditor('')..update([], melosYaml)).toString(),
+    );
+    pubspecFile.writeAsStringSync(
+      (YamlEditor('')..update([], pubspecYaml)).toString(),
+    );
+
+    logger.log(
+      'Initialized Melos workspace in ${dir.path}.\n'
+      'Run the following commands to bootstrap the workspace:\n'
+      '  cd ${dir.path}\n'
+      '  melos bootstrap',
+    );
+  }
+}

packages/melos/lib/src/commands/runner.dart

@@ -17,6 +17,7 @@ import 'package:pubspec/pubspec.dart';
 import 'package:yaml/yaml.dart';
 import 'package:yaml_edit/yaml_edit.dart';
 
+import '../../version.g.dart';
 import '../command_configs/command_configs.dart';
 import '../command_runner/version.dart';
 import '../common/aggregate_changelog.dart';
@@ -52,6 +53,7 @@ part 'run.dart';
 part 'version.dart';
 part 'analyze.dart';
 part 'format.dart';
+part 'init.dart';
 
 enum CommandWithLifecycle {
   bootstrap,
@@ -70,7 +72,8 @@ class Melos extends _Melos
         _VersionMixin,
         _PublishMixin,
         _AnalyzeMixin,
-        _FormatMixin {
+        _FormatMixin,
+        _InitMixin {
   Melos({
     required this.config,
     Logger? logger,
@@ -84,6 +87,7 @@ class Melos extends _Melos
 
 abstract class _Melos {
   MelosLogger get logger;
+
   MelosWorkspaceConfig get config;
 
   Future<MelosWorkspace> createWorkspace({