Add a dart mcp-server command per go/dart-mcp-server-release-plan.

- Adds `dart_mcp` and `dart_mcp_server` as DEPS
- Build an AOT snapshot for the dart_mcp_server executable
- Add top level `mcp-server` command to dartdev (hidden).
- I also did add an `--experimental-mcp-server` flag which is required for this command to actually work. We had initially discussed not doing this due to complexity but I was able to keep it completely scoped to just this command. I can remove it if there are strong opinions though.

Change-Id: I737a5625507f69a904ccd1012682764eb360a2c2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/430900
Reviewed-by: Siva Annamalai <asiva@google.com>
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Jake Macdonald <jakemac@google.com>

DEPS

@@ -129,6 +129,7 @@ vars = {
   ### /third_party/pkg dependencies
   # 'tools/rev_sdk_deps.dart' will rev pkg dependencies to their latest; put an
   # EOL comment after a dependency to instead pin at the current revision.
+  "ai_rev": "93a9191b6eed79d24fc5d3ec9b514f71c888fc41",
   "core_rev": "635dfa32c261ba078438b74de397f2207904ca78", # https://github.com/dart-lang/core/pull/734
   "dartdoc_rev": "e38f392163a4738a21024acd370d104e0efe72f0",
   "ecosystem_rev": "815d4ba2e7d11f8695a26f6cbe1262e3b8ff8d0d",
@@ -327,6 +328,8 @@ deps = {
       Var('chromium_git') + '/external/github.com/mdn/browser-compat-data' +
       "@" + Var("browser-compat-data_tag"),
 
+  Var("dart_root") + "/third_party/pkg/ai":
+      Var("dart_git") + "ai.git" + "@" + Var("ai_rev"),
   Var("dart_root") + "/third_party/pkg/core":
       Var("dart_git") + "core.git" + "@" + Var("core_rev"),
   Var("dart_root") + "/third_party/pkg/dart_style":

pkg/dartdev/lib/dartdev.dart

@@ -20,6 +20,7 @@ import 'src/commands/build.dart';
 import 'src/commands/compilation_server.dart';
 import 'src/commands/compile.dart';
 import 'src/commands/create.dart';
+import 'src/commands/dart_mcp_server.dart';
 import 'src/commands/debug_adapter.dart';
 import 'src/commands/development_service.dart';
 import 'src/commands/devtools.dart';
@@ -118,6 +119,7 @@ class DartdevRunner extends CommandRunner<int> {
     addCommand(FormatCommand(verbose: verbose));
     addCommand(InfoCommand(verbose: verbose));
     addCommand(LanguageServerCommand(verbose: verbose));
+    addCommand(DartMCPServerCommand(verbose: verbose));
     addCommand(pubCommand(isVerbose: () => verbose));
     addCommand(RunCommand(
       verbose: verbose,

pkg/dartdev/lib/src/commands/dart_mcp_server.dart

@@ -0,0 +1,68 @@
+// Copyright (c) 2025, the Dart project authors. Please see the AUTHORS file
+// 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 '../core.dart';
+import '../sdk.dart';
+import '../vm_interop_handler.dart';
+
+class DartMCPServerCommand extends DartdevCommand {
+  static const String cmdName = 'mcp-server';
+
+  static const String cmdDescription = '''
+A stdio based Model Context Protocol (MCP) server to aid in Dart and Flutter development.
+
+EXPERIMENTAL: This tool may change dramatically or disappear at any time.''';
+
+  static const _forceRootsFallbackFlag = 'force-roots-fallback';
+  static const _experimentFlag = 'experimental-mcp-server';
+
+  DartMCPServerCommand({bool verbose = false})
+      : super(cmdName, cmdDescription, verbose, hidden: true) {
+    argParser
+      ..addFlag(
+        _forceRootsFallbackFlag,
+        negatable: true,
+        defaultsTo: false,
+        help:
+            'Forces a behavior for project roots which uses MCP tools instead '
+            'of the native MCP roots. This can be helpful for clients like '
+            'Cursor which claim to have roots support but do not actually '
+            'support it.',
+      )
+      ..addFlag(_experimentFlag,
+          defaultsTo: false,
+          help: 'A required flag in order to use this command. Passing this '
+              'flag is an acknowledgement that you understand it is an '
+              'experimental feature with no stability guarantees.');
+  }
+
+  @override
+  Future<int> run() async {
+    final args = argResults!;
+    if (!args.flag(_experimentFlag)) {
+      log.stderr('Missing required flag --$_experimentFlag\n\n$usage');
+      return 64;
+    }
+    try {
+      VmInteropHandler.run(
+        sdk.dartAotRuntime,
+        [
+          sdk.dartMCPServerAotSnapshot,
+          if (args.flag(_forceRootsFallbackFlag)) '--$_forceRootsFallbackFlag'
+        ],
+        useExecProcess: true,
+      );
+      return 0;
+    } catch (e, st) {
+      log.stderr('Error: launching Dart MCP server failed');
+      log.stderr(e.toString());
+      if (verbose) {
+        log.stderr(st.toString());
+      }
+      return 255;
+    }
+  }
+}

pkg/dartdev/lib/src/sdk.dart

@@ -102,6 +102,10 @@ class Sdk {
         'dart2wasm_product.snapshot',
       );
 
+  String get dartMCPServerAotSnapshot => _snapshotPathFor(
+        'dart_mcp_server_aot.dart.snapshot',
+      );
+
   String get ddsSnapshot => _snapshotPathFor(
         'dds.dart.snapshot',
       );

pubspec.yaml

@@ -143,6 +143,10 @@ dependency_overrides:
     path: third_party/pkg/tools/pkgs/csslib
   dart_flutter_team_lints:
     path: third_party/pkg/ecosystem/pkgs/dart_flutter_team_lints
+  dart_mcp:
+    path: third_party/pkg/ai/pkgs/dart_mcp
+  dart_mcp_server:
+    path: third_party/pkg/ai/pkgs/dart_mcp_server
   dart_style:
     path: third_party/pkg/dart_style
   dartdoc:
@@ -221,6 +225,8 @@ dependency_overrides:
     path: third_party/pkg/tools/pkgs/pool
   protobuf:
     path: third_party/pkg/protobuf/protobuf
+  process:
+    path: third_party/pkg/tools/pkgs/process
   protobuf_benchmarks:
     path: third_party/pkg/protobuf/benchmarks
   protoc_plugin:
@@ -257,6 +263,8 @@ dependency_overrides:
     path: third_party/pkg/tools/pkgs/stack_trace
   stream_channel:
     path: third_party/pkg/tools/pkgs/stream_channel
+  stream_transform:
+    path: third_party/pkg/tools/pkgs/stream_transform
   string_scanner:
     path: third_party/pkg/tools/pkgs/string_scanner
   swift2objc:

sdk/BUILD.gn

@@ -151,6 +151,11 @@ if (dart_target_arch != "ia32" && dart_target_arch != "x86") {
       "../utils/dtd:dtd_aot",
       "dart_tooling_daemon_aot",
     ],
+    [
+      "dart_mcp_server_aot_product",
+      "../utils/dart_mcp_server:dart_mcp_server_aot",
+      "dart_mcp_server_aot",
+    ],
   ]
 } else {
   _platform_sdk_snapshots += [

utils/dart_mcp_server/BUILD.gn

@@ -0,0 +1,31 @@
+# Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+# 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("../../runtime/runtime_args.gni")
+import("../aot_snapshot.gni")
+
+group("dart_mcp_server_aot") {
+  public_deps = [
+    ":dart_mcp_server_aot_product_snapshot",
+    ":dart_mcp_server_aot_snapshot",
+  ]
+}
+
+aot_snapshot("dart_mcp_server_aot_snapshot") {
+  main_dart = "../../third_party/pkg/ai/pkgs/dart_mcp_server/bin/main.dart"
+  output = "$root_gen_dir/dart_mcp_server_aot.dart.snapshot"
+}
+
+aot_snapshot("dart_mcp_server_aot_product_snapshot") {
+  main_dart = "../../third_party/pkg/ai/pkgs/dart_mcp_server/bin/main.dart"
+  output = "$root_gen_dir/dart_mcp_server_aot_product.dart.snapshot"
+
+  # dartaotruntime has dart_product_config applied to it,
+  # so it is built in product mode in both release and
+  # product builds, and is only built in debug mode in debug
+  # builds. The following line ensures that the dartaotruntime
+  # and dart_mcp_server_aot snapshot in an SDK build are
+  # always compatible with each other.
+  force_product_mode = !dart_debug
+}