feat: Init command (#780)

Adds `init` command to melos.

docs/commands/init.mdx

@@ -0,0 +1,93 @@
+---
+title: Init Command
+description: Learn more about the `init` command in Melos.
+---
+
+# Init Command
+
+The `init` command initializes a new Melos workspace.
+It creates the necessary configuration files and
+directory structure for your monorepo.
+
+## Basic Usage
+
+```bash
+melos init [workspace_name]
+```
+
+If no workspace name is provided, you'll be prompted to enter one.
+By default, it uses the current directory name.
+
+## Options
+
+### --directory (-d)
+Specifies the directory where the workspace should be created.
+If not provided, you'll be prompted to enter one.
+Defaults to the workspace name, or current directory ('.')
+if the workspace name matches the current directory name.
+
+```bash
+melos init my_workspace --directory custom_dir
+```
+
+### --packages (-p)
+Defines additional glob patterns for package directories
+to include in the workspace. Accepts comma-separated values and can be
+specified multiple times.
+
+```bash
+melos init --packages "modules/*" --packages "libs/*"
+```
+
+## Interactive Setup
+
+When running `melos init`, you'll be guided through
+an interactive setup process that will:
+
+1. Prompt for a workspace name 
+(if not provided, defaults to current directory name)
+2. Ask for a directory location 
+(defaults to workspace name, or '.' if matching current directory)
+3. Ask if you want to include an `apps` directory (defaults to true)
+
+## Created Files
+
+The command creates the following structure:
+
+```
+<directory>/
+├── melos.yaml    # Workspace configuration
+├── pubspec.yaml  # Root package configuration
+├── packages/     # Packages directory (always created)
+└── apps/         # Apps directory (created if confirmed during setup)
+```
+
+### melos.yaml
+Contains the workspace configuration with:
+- Workspace name
+- Package locations (defaults to ['packages/*'] and optionally 'apps/*')
+- Additional package glob patterns (if specified via --packages)
+
+### pubspec.yaml
+Contains the root package configuration with:
+- Project name (same as workspace name)
+- Dart SDK constraints (based on current Dart version)
+- Melos as a dev dependency
+
+## Example
+
+```bash
+# Basic initialization
+melos init my_workspace
+
+# Custom initialization with options
+melos init my_workspace \
+  --directory custom_dir \
+  --packages "modules/*"
+```
+
+After initialization, you can bootstrap your workspace by running:
+```bash
+cd <directory>
+melos bootstrap
+```

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 +1,58 @@
+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.',
+    );
+  }
+
+  @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 useAppsDir = promptBool(
+      message: 'Do you want to add the apps directory?',
+      defaultsTo: true,
+    );
+
+    final melos = Melos(logger: logger, config: config);
+
+    return melos.init(
+      workspaceName,
+      directory: directory,
+      packages: packages ?? const [],
+      useAppDir: useAppsDir,
+    );
+  }
+}

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

@@ -0,0 +1,62 @@
+part of 'runner.dart';
+
+mixin _InitMixin on _Melos {
+  Future<void> init(
+    String workspaceName, {
+    required String directory,
+    required List<String> packages,
+    required bool useAppDir,
+  }) 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 $directory already exists');
+    } else {
+      dir.createSync(recursive: true);
+      Directory(p.join(dir.absolute.path, 'packages')).createSync();
+      if (useAppDir) {
+        Directory(p.join(dir.absolute.path, 'apps')).createSync();
+      }
+    }
+
+    final dartVersion = utils.currentDartVersion('dart');
+    final melosYaml = <String, Object?>{
+      'name': qualifiedWorkspaceName,
+      'packages': [if (useAppDir) 'apps/*', 'packages/*'],
+      if (packages.isNotEmpty) 'packages': packages,
+    };
+    final pubspecYaml = <String, dynamic>{
+      'name': qualifiedWorkspaceName,
+      'environment': {
+        'sdk': '>=$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 ${dir.path}.\n'
+      'Run the following commands to bootstrap the workspace when you have created some packages and/or apps:\n'
+      '${isCurrentDir ? '' : '  cd ${dir.path}\n'}'
+      '  melos bootstrap',
+    );
+  }
+}

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

@@ -17,6 +17,7 @@ import 'package:pubspec_parse/pubspec_parse.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';
@@ -51,6 +52,7 @@ part 'bootstrap.dart';
 part 'clean.dart';
 part 'exec.dart';
 part 'format.dart';
+part 'init.dart';
 part 'list.dart';
 part 'publish.dart';
 part 'run.dart';
@@ -73,7 +75,8 @@ class Melos extends _Melos
         _VersionMixin,
         _PublishMixin,
         _AnalyzeMixin,
-        _FormatMixin {
+        _FormatMixin,
+        _InitMixin {
   Melos({
     required this.config,
     Logger? logger,

packages/melos/lib/src/workspace_configs.dart

@@ -376,6 +376,17 @@ class MelosWorkspaceConfig {
           commands: CommandConfigs.empty,
         );
 
+  @visibleForTesting
+  MelosWorkspaceConfig.emptyWith({
+    String? name,
+    String? path,
+  }) : this(
+          name: name ?? 'Melos',
+          packages: [],
+          path: path ?? Directory.current.path,
+          commands: CommandConfigs.empty,
+        );
+
   /// Loads the [MelosWorkspaceConfig] for the workspace at [workspaceRoot].
   static Future<MelosWorkspaceConfig> fromWorkspaceRoot(
     Directory workspaceRoot,