Invoke dart/flutter in a more robust way (#143)

Closes #33

Adds --dart-sdk and --flutter-sdk arguments to the CLI, falling back on DART_SDK and FLUTTER_SDK environment variables, and finally `Platform.resolvedExecutable`.

The flutter SDK will also be looked up relative to the Dart SDK, if a location is not given by command line arg or environment.

Author: jakemac53

pkgs/dart_mcp_server/bin/main.dart

@@ -20,9 +20,14 @@ void main(List<String> args) async {
   }
 
   DartMCPServer? server;
-  await runZonedGuarded(
-    () async {
-      server = await DartMCPServer.connect(
+  final dartSdkPath =
+      parsedArgs.option(dartSdkOption) ?? io.Platform.environment['DART_SDK'];
+  final flutterSdkPath =
+      parsedArgs.option(flutterSdkOption) ??
+      io.Platform.environment['FLUTTER_SDK'];
+  runZonedGuarded(
+    () {
+      server = DartMCPServer(
         StreamChannel.withCloseGuarantee(io.stdin, io.stdout)
             .transform(StreamChannelTransformer.fromCodec(utf8))
             .transformStream(const LineSplitter())
@@ -34,6 +39,7 @@ void main(List<String> args) async {
               ),
             ),
         forceRootsFallback: parsedArgs.flag(forceRootsFallback),
+        sdk: Sdk.find(dartSdkPath: dartSdkPath, flutterSdkPath: flutterSdkPath),
       );
     },
     (e, s) {
@@ -65,6 +71,19 @@ void main(List<String> args) async {
 
 final argParser =
     ArgParser(allowTrailingOptions: false)
+      ..addOption(
+        dartSdkOption,
+        help:
+            'The path to the root of the desired Dart SDK. Defaults to the '
+            'DART_SDK environment variable.',
+      )
+      ..addOption(
+        flutterSdkOption,
+        help:
+            'The path to the root of the desired Flutter SDK. Defaults to '
+            'the FLUTTER_SDK environment variable, then searching up from the '
+            'Dart SDK.',
+      )
       ..addFlag(
         forceRootsFallback,
         negatable: true,
@@ -77,5 +96,7 @@ final argParser =
       )
       ..addFlag(help, abbr: 'h', help: 'Show usage text');
 
+const dartSdkOption = 'dart-sdk';
+const flutterSdkOption = 'flutter-sdk';
 const forceRootsFallback = 'force-roots-fallback';
 const help = 'help';

pkgs/dart_mcp_server/lib/dart_mcp_server.dart

@@ -3,3 +3,4 @@
 // BSD-style license that can be found in the LICENSE file.
 
 export 'src/server.dart';
+export 'src/utils/sdk.dart' show Sdk;

pkgs/dart_mcp_server/lib/src/mixins/analyzer.dart

@@ -14,13 +14,15 @@ import 'package:meta/meta.dart';
 
 import '../lsp/wire_format.dart';
 import '../utils/constants.dart';
+import '../utils/sdk.dart';
 
 /// Mix this in to any MCPServer to add support for analyzing Dart projects.
 ///
 /// The MCPServer must already have the [ToolsSupport] and [LoggingSupport]
 /// mixins applied.
 base mixin DartAnalyzerSupport
-    on ToolsSupport, LoggingSupport, RootsTrackingSupport {
+    on ToolsSupport, LoggingSupport, RootsTrackingSupport
+    implements SdkSupport {
   /// The LSP server connection for the analysis server.
   late final Peer _lspConnection;
 
@@ -52,9 +54,8 @@ base mixin DartAnalyzerSupport
       if (!supportsRoots)
         'Project analysis requires the "roots" capability which is not '
             'supported. Analysis tools have been disabled.',
-      if (Platform.environment['DART_SDK'] == null)
-        'Project analysis requires a "DART_SDK" environment variable to be set '
-            '(this should be the path to the root of the dart SDK). Analysis '
+      if (sdk.dartSdkPath == null)
+        'Project analysis requires a Dart SDK but none was given. Analysis '
             'tools have been disabled.',
     ];
 
@@ -90,7 +91,7 @@ base mixin DartAnalyzerSupport
   ///
   /// On failure, returns a reason for the failure.
   Future<String?> _initializeAnalyzerLspServer() async {
-    _lspServer = await Process.start('dart', [
+    _lspServer = await Process.start(sdk.dartExecutablePath, [
       'language-server',
       // Required even though it is documented as the default.
       // https://github.com/dart-lang/sdk/issues/60574

pkgs/dart_mcp_server/lib/src/mixins/dash_cli.dart

@@ -11,21 +11,22 @@ import '../utils/cli_utils.dart';
 import '../utils/constants.dart';
 import '../utils/file_system.dart';
 import '../utils/process_manager.dart';
+import '../utils/sdk.dart';
 
 /// Mix this in to any MCPServer to add support for running Dart or Flutter CLI
 /// commands like `dart fix`, `dart format`, and `flutter test`.
 ///
 /// The MCPServer must already have the [ToolsSupport] and [LoggingSupport]
 /// mixins applied.
 base mixin DashCliSupport on ToolsSupport, LoggingSupport, RootsTrackingSupport
-    implements ProcessManagerSupport, FileSystemSupport {
+    implements ProcessManagerSupport, FileSystemSupport, SdkSupport {
   @override
   FutureOr<InitializeResult> initialize(InitializeRequest request) {
     try {
       return super.initialize(request);
     } finally {
-      // Can't call this until after `super.initialize`.
-      if (supportsRoots) {
+      // Can't call `supportsRoots` until after `super.initialize`.
+      if (supportsRoots && sdk.dartSdkPath != null) {
         registerTool(dartFixTool, _runDartFixTool);
         registerTool(dartFormatTool, _runDartFormatTool);
         registerTool(runTestsTool, _runTests);
@@ -38,26 +39,28 @@ base mixin DashCliSupport on ToolsSupport, LoggingSupport, RootsTrackingSupport
   Future<CallToolResult> _runDartFixTool(CallToolRequest request) async {
     return runCommandInRoots(
       request,
-      commandForRoot: (_, _) => 'dart',
+      commandForRoot: (_, _, sdk) => sdk.dartExecutablePath,
       arguments: ['fix', '--apply'],
       commandDescription: 'dart fix',
       processManager: processManager,
       knownRoots: await roots,
       fileSystem: fileSystem,
+      sdk: sdk,
     );
   }
 
   /// Implementation of the [dartFormatTool].
   Future<CallToolResult> _runDartFormatTool(CallToolRequest request) async {
     return runCommandInRoots(
       request,
-      commandForRoot: (_, _) => 'dart',
+      commandForRoot: (_, _, sdk) => sdk.dartExecutablePath,
       arguments: ['format'],
       commandDescription: 'dart format',
       processManager: processManager,
       defaultPaths: ['.'],
       knownRoots: await roots,
       fileSystem: fileSystem,
+      sdk: sdk,
     );
   }
 
@@ -70,6 +73,7 @@ base mixin DashCliSupport on ToolsSupport, LoggingSupport, RootsTrackingSupport
       processManager: processManager,
       knownRoots: await roots,
       fileSystem: fileSystem,
+      sdk: sdk,
     );
   }
 
@@ -119,11 +123,19 @@ base mixin DashCliSupport on ToolsSupport, LoggingSupport, RootsTrackingSupport
     return runCommandInRoot(
       request,
       arguments: commandArgs,
-      commandForRoot: (_, _) => projectType!,
+      commandForRoot:
+          (_, _, sdk) =>
+              switch (projectType) {
+                    'dart' => sdk.dartExecutablePath,
+                    'flutter' => sdk.flutterExecutablePath,
+                    _ => StateError('Unknown project type: $projectType'),
+                  }
+                  as String,
       commandDescription: '$projectType create',
       fileSystem: fileSystem,
       processManager: processManager,
       knownRoots: await roots,
+      sdk: sdk,
     );
   }
 

pkgs/dart_mcp_server/lib/src/mixins/pub.dart

@@ -10,6 +10,7 @@ import '../utils/cli_utils.dart';
 import '../utils/constants.dart';
 import '../utils/file_system.dart';
 import '../utils/process_manager.dart';
+import '../utils/sdk.dart';
 
 /// Mix this in to any MCPServer to add support for running Pub commands like
 /// like `pub add` and `pub get`.
@@ -19,7 +20,7 @@ import '../utils/process_manager.dart';
 /// The MCPServer must already have the [ToolsSupport] and [LoggingSupport]
 /// mixins applied.
 base mixin PubSupport on ToolsSupport, LoggingSupport, RootsTrackingSupport
-    implements ProcessManagerSupport, FileSystemSupport {
+    implements ProcessManagerSupport, FileSystemSupport, SdkSupport {
   @override
   FutureOr<InitializeResult> initialize(InitializeRequest request) {
     try {
@@ -79,6 +80,7 @@ base mixin PubSupport on ToolsSupport, LoggingSupport, RootsTrackingSupport
       processManager: processManager,
       knownRoots: await roots,
       fileSystem: fileSystem,
+      sdk: sdk,
     );
   }
 

pkgs/dart_mcp_server/lib/src/server.dart

@@ -2,14 +2,11 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:async';
-
 import 'package:dart_mcp/server.dart';
 import 'package:file/file.dart';
 import 'package:file/local.dart';
 import 'package:meta/meta.dart';
 import 'package:process/process.dart';
-import 'package:stream_channel/stream_channel.dart';
 
 import 'mixins/analyzer.dart';
 import 'mixins/dash_cli.dart';
@@ -19,6 +16,7 @@ import 'mixins/pub_dev_search.dart';
 import 'mixins/roots_fallback_support.dart';
 import 'utils/file_system.dart';
 import 'utils/process_manager.dart';
+import 'utils/sdk.dart';
 
 /// An MCP server for Dart and Flutter tooling.
 final class DartMCPServer extends MCPServer
@@ -33,9 +31,10 @@ final class DartMCPServer extends MCPServer
         PubSupport,
         PubDevSupport,
         DartToolingDaemonSupport
-    implements ProcessManagerSupport, FileSystemSupport {
+    implements ProcessManagerSupport, FileSystemSupport, SdkSupport {
   DartMCPServer(
     super.channel, {
+    required this.sdk,
     @visibleForTesting this.processManager = const LocalProcessManager(),
     @visibleForTesting this.fileSystem = const LocalFileSystem(),
     this.forceRootsFallback = false,
@@ -49,13 +48,6 @@ final class DartMCPServer extends MCPServer
              'their development tools and running applications.',
        );
 
-  static Future<DartMCPServer> connect(
-    StreamChannel<String> mcpChannel, {
-    bool forceRootsFallback = false,
-  }) async {
-    return DartMCPServer(mcpChannel, forceRootsFallback: forceRootsFallback);
-  }
-
   @override
   final LocalProcessManager processManager;
 
@@ -64,4 +56,7 @@ final class DartMCPServer extends MCPServer
 
   @override
   final bool forceRootsFallback;
+
+  @override
+  final Sdk sdk;
 }

pkgs/dart_mcp_server/lib/src/utils/cli_utils.dart

@@ -11,6 +11,7 @@ import 'package:process/process.dart';
 import 'package:yaml/yaml.dart';
 
 import 'constants.dart';
+import 'sdk.dart';
 
 /// The supported kinds of projects.
 enum ProjectKind {
@@ -71,14 +72,15 @@ Future<ProjectKind> inferProjectKind(Root root, FileSystem fileSystem) async {
 /// root's 'paths'.
 Future<CallToolResult> runCommandInRoots(
   CallToolRequest request, {
-  FutureOr<String> Function(Root, FileSystem) commandForRoot =
+  FutureOr<String> Function(Root, FileSystem, Sdk) commandForRoot =
       defaultCommandForRoot,
   List<String> arguments = const [],
   required String commandDescription,
   required FileSystem fileSystem,
   required ProcessManager processManager,
   required List<Root> knownRoots,
   List<String> defaultPaths = const <String>[],
+  required Sdk sdk,
 }) async {
   var rootConfigs =
       (request.arguments?[ParameterNames.roots] as List?)
@@ -103,6 +105,7 @@ Future<CallToolResult> runCommandInRoots(
       processManager: processManager,
       knownRoots: knownRoots,
       defaultPaths: defaultPaths,
+      sdk: sdk,
     );
     if (result.isError == true) return result;
     outputs.addAll(result.content);
@@ -134,14 +137,15 @@ Future<CallToolResult> runCommandInRoots(
 Future<CallToolResult> runCommandInRoot(
   CallToolRequest request, {
   Map<String, Object?>? rootConfig,
-  FutureOr<String> Function(Root, FileSystem) commandForRoot =
+  FutureOr<String> Function(Root, FileSystem, Sdk) commandForRoot =
       defaultCommandForRoot,
   List<String> arguments = const [],
   required String commandDescription,
   required FileSystem fileSystem,
   required ProcessManager processManager,
   required List<Root> knownRoots,
   List<String> defaultPaths = const <String>[],
+  required Sdk sdk,
 }) async {
   rootConfig ??= request.arguments;
   final rootUriString = rootConfig?[ParameterNames.root] as String?;
@@ -185,7 +189,7 @@ Future<CallToolResult> runCommandInRoot(
   final projectRoot = fileSystem.directory(rootUri);
 
   final commandWithPaths = <String>[
-    await commandForRoot(root, fileSystem),
+    await commandForRoot(root, fileSystem, sdk),
     ...arguments,
   ];
   final paths =
@@ -240,18 +244,21 @@ Future<CallToolResult> runCommandInRoot(
 /// Returns 'dart' or 'flutter' based on the pubspec contents.
 ///
 /// Throws an [ArgumentError] if there is no pubspec.
-Future<String> defaultCommandForRoot(Root root, FileSystem fileSystem) async =>
-    switch (await inferProjectKind(root, fileSystem)) {
-      ProjectKind.dart => 'dart',
-      ProjectKind.flutter => 'flutter',
-      ProjectKind.unknown =>
-        throw ArgumentError.value(
-          root.uri,
-          'root.uri',
-          'Unknown project kind at root ${root.uri}. All projects must have a '
-              'pubspec.',
-        ),
-    };
+Future<String> defaultCommandForRoot(
+  Root root,
+  FileSystem fileSystem,
+  Sdk sdk,
+) async => switch (await inferProjectKind(root, fileSystem)) {
+  ProjectKind.dart => sdk.dartExecutablePath,
+  ProjectKind.flutter => sdk.flutterExecutablePath,
+  ProjectKind.unknown =>
+    throw ArgumentError.value(
+      root.uri,
+      'root.uri',
+      'Unknown project kind at root ${root.uri}. All projects must have a '
+          'pubspec.',
+    ),
+};
 
 /// Returns whether or not [rootUri] is an allowed root, either exactly matching
 /// or under on of the [knownRoots].