diff --git a/pkg/analysis_server/lib/lsp_protocol/protocol_custom_generated.dart b/pkg/analysis_server/lib/lsp_protocol/protocol_custom_generated.dart
index e3c0fe58c1c..8c4ec6d0dcf 100644
--- a/pkg/analysis_server/lib/lsp_protocol/protocol_custom_generated.dart
+++ b/pkg/analysis_server/lib/lsp_protocol/protocol_custom_generated.dart
@@ -1087,6 +1087,361 @@ class FlutterOutlineAttribute implements ToJsonable {
   String toString() => jsonEncoder.convert(toJson());
 }
 
+class IncomingMessage implements Message, ToJsonable {
+  static const jsonHandler = LspJsonHandler(
+    IncomingMessage.canParse,
+    IncomingMessage.fromJson,
+  );
+
+  IncomingMessage({
+    this.clientRequestTime,
+    required this.jsonrpc,
+    required this.method,
+    this.params,
+  });
+  static IncomingMessage fromJson(Map<String, Object?> json) {
+    if (RequestMessage.canParse(json, nullLspJsonReporter)) {
+      return RequestMessage.fromJson(json);
+    }
+    if (NotificationMessage.canParse(json, nullLspJsonReporter)) {
+      return NotificationMessage.fromJson(json);
+    }
+    final clientRequestTimeJson = json['clientRequestTime'];
+    final clientRequestTime = clientRequestTimeJson as int?;
+    final jsonrpcJson = json['jsonrpc'];
+    final jsonrpc = jsonrpcJson as String;
+    final methodJson = json['method'];
+    final method = Method.fromJson(methodJson as String);
+    final paramsJson = json['params'];
+    final params = paramsJson;
+    return IncomingMessage(
+      clientRequestTime: clientRequestTime,
+      jsonrpc: jsonrpc,
+      method: method,
+      params: params,
+    );
+  }
+
+  final int? clientRequestTime;
+  final String jsonrpc;
+  final Method method;
+  final Object? params;
+
+  Map<String, Object?> toJson() {
+    var __result = <String, Object?>{};
+    if (clientRequestTime != null) {
+      __result['clientRequestTime'] = clientRequestTime;
+    }
+    __result['jsonrpc'] = jsonrpc;
+    __result['method'] = method.toJson();
+    if (params != null) {
+      __result['params'] = params;
+    }
+    return __result;
+  }
+
+  static bool canParse(Object? obj, LspJsonReporter reporter) {
+    if (obj is Map<String, Object?>) {
+      reporter.push('clientRequestTime');
+      try {
+        final clientRequestTime = obj['clientRequestTime'];
+        if (clientRequestTime != null && !(clientRequestTime is int)) {
+          reporter.reportError('must be of type int');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('jsonrpc');
+      try {
+        if (!obj.containsKey('jsonrpc')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final jsonrpc = obj['jsonrpc'];
+        if (jsonrpc == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(jsonrpc is String)) {
+          reporter.reportError('must be of type String');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('method');
+      try {
+        if (!obj.containsKey('method')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final method = obj['method'];
+        if (method == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(Method.canParse(method, reporter))) {
+          reporter.reportError('must be of type Method');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      return true;
+    } else {
+      reporter.reportError('must be of type IncomingMessage');
+      return false;
+    }
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is IncomingMessage && other.runtimeType == IncomingMessage) {
+      return clientRequestTime == other.clientRequestTime &&
+          jsonrpc == other.jsonrpc &&
+          method == other.method &&
+          params == other.params &&
+          true;
+    }
+    return false;
+  }
+
+  @override
+  int get hashCode => Object.hash(
+        clientRequestTime,
+        jsonrpc,
+        method,
+        params,
+      );
+
+  @override
+  String toString() => jsonEncoder.convert(toJson());
+}
+
+class Message implements ToJsonable {
+  static const jsonHandler = LspJsonHandler(
+    Message.canParse,
+    Message.fromJson,
+  );
+
+  Message({
+    this.clientRequestTime,
+    required this.jsonrpc,
+  });
+  static Message fromJson(Map<String, Object?> json) {
+    if (IncomingMessage.canParse(json, nullLspJsonReporter)) {
+      return IncomingMessage.fromJson(json);
+    }
+    if (ResponseMessage.canParse(json, nullLspJsonReporter)) {
+      return ResponseMessage.fromJson(json);
+    }
+    final clientRequestTimeJson = json['clientRequestTime'];
+    final clientRequestTime = clientRequestTimeJson as int?;
+    final jsonrpcJson = json['jsonrpc'];
+    final jsonrpc = jsonrpcJson as String;
+    return Message(
+      clientRequestTime: clientRequestTime,
+      jsonrpc: jsonrpc,
+    );
+  }
+
+  final int? clientRequestTime;
+  final String jsonrpc;
+
+  Map<String, Object?> toJson() {
+    var __result = <String, Object?>{};
+    if (clientRequestTime != null) {
+      __result['clientRequestTime'] = clientRequestTime;
+    }
+    __result['jsonrpc'] = jsonrpc;
+    return __result;
+  }
+
+  static bool canParse(Object? obj, LspJsonReporter reporter) {
+    if (obj is Map<String, Object?>) {
+      reporter.push('clientRequestTime');
+      try {
+        final clientRequestTime = obj['clientRequestTime'];
+        if (clientRequestTime != null && !(clientRequestTime is int)) {
+          reporter.reportError('must be of type int');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('jsonrpc');
+      try {
+        if (!obj.containsKey('jsonrpc')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final jsonrpc = obj['jsonrpc'];
+        if (jsonrpc == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(jsonrpc is String)) {
+          reporter.reportError('must be of type String');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      return true;
+    } else {
+      reporter.reportError('must be of type Message');
+      return false;
+    }
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is Message && other.runtimeType == Message) {
+      return clientRequestTime == other.clientRequestTime &&
+          jsonrpc == other.jsonrpc &&
+          true;
+    }
+    return false;
+  }
+
+  @override
+  int get hashCode => Object.hash(
+        clientRequestTime,
+        jsonrpc,
+      );
+
+  @override
+  String toString() => jsonEncoder.convert(toJson());
+}
+
+class NotificationMessage implements IncomingMessage, ToJsonable {
+  static const jsonHandler = LspJsonHandler(
+    NotificationMessage.canParse,
+    NotificationMessage.fromJson,
+  );
+
+  NotificationMessage({
+    this.clientRequestTime,
+    required this.jsonrpc,
+    required this.method,
+    this.params,
+  });
+  static NotificationMessage fromJson(Map<String, Object?> json) {
+    final clientRequestTimeJson = json['clientRequestTime'];
+    final clientRequestTime = clientRequestTimeJson as int?;
+    final jsonrpcJson = json['jsonrpc'];
+    final jsonrpc = jsonrpcJson as String;
+    final methodJson = json['method'];
+    final method = Method.fromJson(methodJson as String);
+    final paramsJson = json['params'];
+    final params = paramsJson;
+    return NotificationMessage(
+      clientRequestTime: clientRequestTime,
+      jsonrpc: jsonrpc,
+      method: method,
+      params: params,
+    );
+  }
+
+  final int? clientRequestTime;
+  final String jsonrpc;
+  final Method method;
+  final Object? params;
+
+  Map<String, Object?> toJson() {
+    var __result = <String, Object?>{};
+    if (clientRequestTime != null) {
+      __result['clientRequestTime'] = clientRequestTime;
+    }
+    __result['jsonrpc'] = jsonrpc;
+    __result['method'] = method.toJson();
+    if (params != null) {
+      __result['params'] = params;
+    }
+    return __result;
+  }
+
+  static bool canParse(Object? obj, LspJsonReporter reporter) {
+    if (obj is Map<String, Object?>) {
+      reporter.push('clientRequestTime');
+      try {
+        final clientRequestTime = obj['clientRequestTime'];
+        if (clientRequestTime != null && !(clientRequestTime is int)) {
+          reporter.reportError('must be of type int');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('jsonrpc');
+      try {
+        if (!obj.containsKey('jsonrpc')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final jsonrpc = obj['jsonrpc'];
+        if (jsonrpc == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(jsonrpc is String)) {
+          reporter.reportError('must be of type String');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('method');
+      try {
+        if (!obj.containsKey('method')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final method = obj['method'];
+        if (method == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(Method.canParse(method, reporter))) {
+          reporter.reportError('must be of type Method');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      return true;
+    } else {
+      reporter.reportError('must be of type NotificationMessage');
+      return false;
+    }
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is NotificationMessage &&
+        other.runtimeType == NotificationMessage) {
+      return clientRequestTime == other.clientRequestTime &&
+          jsonrpc == other.jsonrpc &&
+          method == other.method &&
+          params == other.params &&
+          true;
+    }
+    return false;
+  }
+
+  @override
+  int get hashCode => Object.hash(
+        clientRequestTime,
+        jsonrpc,
+        method,
+        params,
+      );
+
+  @override
+  String toString() => jsonEncoder.convert(toJson());
+}
+
 class Outline implements ToJsonable {
   static const jsonHandler = LspJsonHandler(
     Outline.canParse,
@@ -1598,6 +1953,432 @@ class PublishOutlineParams implements ToJsonable {
   String toString() => jsonEncoder.convert(toJson());
 }
 
+class RequestMessage implements IncomingMessage, ToJsonable {
+  static const jsonHandler = LspJsonHandler(
+    RequestMessage.canParse,
+    RequestMessage.fromJson,
+  );
+
+  RequestMessage({
+    this.clientRequestTime,
+    required this.id,
+    required this.jsonrpc,
+    required this.method,
+    this.params,
+  });
+  static RequestMessage fromJson(Map<String, Object?> json) {
+    final clientRequestTimeJson = json['clientRequestTime'];
+    final clientRequestTime = clientRequestTimeJson as int?;
+    final idJson = json['id'];
+    final id = idJson is int
+        ? Either2<int, String>.t1(idJson)
+        : (idJson is String
+            ? Either2<int, String>.t2(idJson)
+            : (throw '''$idJson was not one of (int, String)'''));
+    final jsonrpcJson = json['jsonrpc'];
+    final jsonrpc = jsonrpcJson as String;
+    final methodJson = json['method'];
+    final method = Method.fromJson(methodJson as String);
+    final paramsJson = json['params'];
+    final params = paramsJson;
+    return RequestMessage(
+      clientRequestTime: clientRequestTime,
+      id: id,
+      jsonrpc: jsonrpc,
+      method: method,
+      params: params,
+    );
+  }
+
+  final int? clientRequestTime;
+  final Either2<int, String> id;
+  final String jsonrpc;
+  final Method method;
+  final Object? params;
+
+  Map<String, Object?> toJson() {
+    var __result = <String, Object?>{};
+    if (clientRequestTime != null) {
+      __result['clientRequestTime'] = clientRequestTime;
+    }
+    __result['id'] = id;
+    __result['jsonrpc'] = jsonrpc;
+    __result['method'] = method.toJson();
+    if (params != null) {
+      __result['params'] = params;
+    }
+    return __result;
+  }
+
+  static bool canParse(Object? obj, LspJsonReporter reporter) {
+    if (obj is Map<String, Object?>) {
+      reporter.push('clientRequestTime');
+      try {
+        final clientRequestTime = obj['clientRequestTime'];
+        if (clientRequestTime != null && !(clientRequestTime is int)) {
+          reporter.reportError('must be of type int');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('id');
+      try {
+        if (!obj.containsKey('id')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final id = obj['id'];
+        if (id == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!((id is int || id is String))) {
+          reporter.reportError('must be of type Either2<int, String>');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('jsonrpc');
+      try {
+        if (!obj.containsKey('jsonrpc')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final jsonrpc = obj['jsonrpc'];
+        if (jsonrpc == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(jsonrpc is String)) {
+          reporter.reportError('must be of type String');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('method');
+      try {
+        if (!obj.containsKey('method')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final method = obj['method'];
+        if (method == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(Method.canParse(method, reporter))) {
+          reporter.reportError('must be of type Method');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      return true;
+    } else {
+      reporter.reportError('must be of type RequestMessage');
+      return false;
+    }
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is RequestMessage && other.runtimeType == RequestMessage) {
+      return clientRequestTime == other.clientRequestTime &&
+          id == other.id &&
+          jsonrpc == other.jsonrpc &&
+          method == other.method &&
+          params == other.params &&
+          true;
+    }
+    return false;
+  }
+
+  @override
+  int get hashCode => Object.hash(
+        clientRequestTime,
+        id,
+        jsonrpc,
+        method,
+        params,
+      );
+
+  @override
+  String toString() => jsonEncoder.convert(toJson());
+}
+
+class ResponseError implements ToJsonable {
+  static const jsonHandler = LspJsonHandler(
+    ResponseError.canParse,
+    ResponseError.fromJson,
+  );
+
+  ResponseError({
+    required this.code,
+    this.data,
+    required this.message,
+  });
+  static ResponseError fromJson(Map<String, Object?> json) {
+    final codeJson = json['code'];
+    final code = ErrorCodes.fromJson(codeJson as int);
+    final dataJson = json['data'];
+    final data = dataJson as String?;
+    final messageJson = json['message'];
+    final message = messageJson as String;
+    return ResponseError(
+      code: code,
+      data: data,
+      message: message,
+    );
+  }
+
+  final ErrorCodes code;
+
+  /// A string that contains additional information about the error. Can be
+  /// omitted.
+  final String? data;
+  final String message;
+
+  Map<String, Object?> toJson() {
+    var __result = <String, Object?>{};
+    __result['code'] = code.toJson();
+    if (data != null) {
+      __result['data'] = data;
+    }
+    __result['message'] = message;
+    return __result;
+  }
+
+  static bool canParse(Object? obj, LspJsonReporter reporter) {
+    if (obj is Map<String, Object?>) {
+      reporter.push('code');
+      try {
+        if (!obj.containsKey('code')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final code = obj['code'];
+        if (code == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(ErrorCodes.canParse(code, reporter))) {
+          reporter.reportError('must be of type ErrorCodes');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('data');
+      try {
+        final data = obj['data'];
+        if (data != null && !(data is String)) {
+          reporter.reportError('must be of type String');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('message');
+      try {
+        if (!obj.containsKey('message')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final message = obj['message'];
+        if (message == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(message is String)) {
+          reporter.reportError('must be of type String');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      return true;
+    } else {
+      reporter.reportError('must be of type ResponseError');
+      return false;
+    }
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is ResponseError && other.runtimeType == ResponseError) {
+      return code == other.code &&
+          data == other.data &&
+          message == other.message &&
+          true;
+    }
+    return false;
+  }
+
+  @override
+  int get hashCode => Object.hash(
+        code,
+        data,
+        message,
+      );
+
+  @override
+  String toString() => jsonEncoder.convert(toJson());
+}
+
+class ResponseMessage implements Message, ToJsonable {
+  static const jsonHandler = LspJsonHandler(
+    ResponseMessage.canParse,
+    ResponseMessage.fromJson,
+  );
+
+  ResponseMessage({
+    this.clientRequestTime,
+    this.error,
+    this.id,
+    required this.jsonrpc,
+    this.result,
+  });
+  static ResponseMessage fromJson(Map<String, Object?> json) {
+    final clientRequestTimeJson = json['clientRequestTime'];
+    final clientRequestTime = clientRequestTimeJson as int?;
+    final errorJson = json['error'];
+    final error = errorJson != null
+        ? ResponseError.fromJson(errorJson as Map<String, Object?>)
+        : null;
+    final idJson = json['id'];
+    final id = idJson == null
+        ? null
+        : (idJson is int
+            ? Either2<int, String>.t1(idJson)
+            : (idJson is String
+                ? Either2<int, String>.t2(idJson)
+                : (throw '''$idJson was not one of (int, String)''')));
+    final jsonrpcJson = json['jsonrpc'];
+    final jsonrpc = jsonrpcJson as String;
+    final resultJson = json['result'];
+    final result = resultJson;
+    return ResponseMessage(
+      clientRequestTime: clientRequestTime,
+      error: error,
+      id: id,
+      jsonrpc: jsonrpc,
+      result: result,
+    );
+  }
+
+  final int? clientRequestTime;
+  final ResponseError? error;
+  final Either2<int, String>? id;
+  final String jsonrpc;
+  final Object? result;
+
+  Map<String, Object?> toJson() {
+    var __result = <String, Object?>{};
+    if (clientRequestTime != null) {
+      __result['clientRequestTime'] = clientRequestTime;
+    }
+    __result['id'] = id;
+    __result['jsonrpc'] = jsonrpc;
+    if (error != null && result != null) {
+      throw 'result and error cannot both be set';
+    } else if (error != null) {
+      __result['error'] = error;
+    } else {
+      __result['result'] = result;
+    }
+    return __result;
+  }
+
+  static bool canParse(Object? obj, LspJsonReporter reporter) {
+    if (obj is Map<String, Object?>) {
+      reporter.push('clientRequestTime');
+      try {
+        final clientRequestTime = obj['clientRequestTime'];
+        if (clientRequestTime != null && !(clientRequestTime is int)) {
+          reporter.reportError('must be of type int');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('error');
+      try {
+        final error = obj['error'];
+        if (error != null && !(ResponseError.canParse(error, reporter))) {
+          reporter.reportError('must be of type ResponseError');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('id');
+      try {
+        if (!obj.containsKey('id')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final id = obj['id'];
+        if (id != null && !((id is int || id is String))) {
+          reporter.reportError('must be of type Either2<int, String>');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      reporter.push('jsonrpc');
+      try {
+        if (!obj.containsKey('jsonrpc')) {
+          reporter.reportError('must not be undefined');
+          return false;
+        }
+        final jsonrpc = obj['jsonrpc'];
+        if (jsonrpc == null) {
+          reporter.reportError('must not be null');
+          return false;
+        }
+        if (!(jsonrpc is String)) {
+          reporter.reportError('must be of type String');
+          return false;
+        }
+      } finally {
+        reporter.pop();
+      }
+      return true;
+    } else {
+      reporter.reportError('must be of type ResponseMessage');
+      return false;
+    }
+  }
+
+  @override
+  bool operator ==(Object other) {
+    if (other is ResponseMessage && other.runtimeType == ResponseMessage) {
+      return clientRequestTime == other.clientRequestTime &&
+          error == other.error &&
+          id == other.id &&
+          jsonrpc == other.jsonrpc &&
+          result == other.result &&
+          true;
+    }
+    return false;
+  }
+
+  @override
+  int get hashCode => Object.hash(
+        clientRequestTime,
+        error,
+        id,
+        jsonrpc,
+        result,
+      );
+
+  @override
+  String toString() => jsonEncoder.convert(toJson());
+}
+
 class SnippetTextEdit implements TextEdit, ToJsonable {
   static const jsonHandler = LspJsonHandler(
     SnippetTextEdit.canParse,
diff --git a/pkg/analysis_server/lib/lsp_protocol/protocol_generated.dart b/pkg/analysis_server/lib/lsp_protocol/protocol_generated.dart
index 4f055635f77..84ccaaca635 100644
--- a/pkg/analysis_server/lib/lsp_protocol/protocol_generated.dart
+++ b/pkg/analysis_server/lib/lsp_protocol/protocol_generated.dart
@@ -23783,105 +23783,6 @@ class MarkupKind implements ToJsonable {
   bool operator ==(Object o) => o is MarkupKind && o._value == _value;
 }
 
-class Message implements ToJsonable {
-  static const jsonHandler = LspJsonHandler(
-    Message.canParse,
-    Message.fromJson,
-  );
-
-  Message({
-    this.clientRequestTime,
-    required this.jsonrpc,
-  });
-  static Message fromJson(Map<String, Object?> json) {
-    if (RequestMessage.canParse(json, nullLspJsonReporter)) {
-      return RequestMessage.fromJson(json);
-    }
-    if (NotificationMessage.canParse(json, nullLspJsonReporter)) {
-      return NotificationMessage.fromJson(json);
-    }
-    if (ResponseMessage.canParse(json, nullLspJsonReporter)) {
-      return ResponseMessage.fromJson(json);
-    }
-    final clientRequestTimeJson = json['clientRequestTime'];
-    final clientRequestTime = clientRequestTimeJson as int?;
-    final jsonrpcJson = json['jsonrpc'];
-    final jsonrpc = jsonrpcJson as String;
-    return Message(
-      clientRequestTime: clientRequestTime,
-      jsonrpc: jsonrpc,
-    );
-  }
-
-  final int? clientRequestTime;
-  final String jsonrpc;
-
-  Map<String, Object?> toJson() {
-    var __result = <String, Object?>{};
-    if (clientRequestTime != null) {
-      __result['clientRequestTime'] = clientRequestTime;
-    }
-    __result['jsonrpc'] = jsonrpc;
-    return __result;
-  }
-
-  static bool canParse(Object? obj, LspJsonReporter reporter) {
-    if (obj is Map<String, Object?>) {
-      reporter.push('clientRequestTime');
-      try {
-        final clientRequestTime = obj['clientRequestTime'];
-        if (clientRequestTime != null && !(clientRequestTime is int)) {
-          reporter.reportError('must be of type int');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('jsonrpc');
-      try {
-        if (!obj.containsKey('jsonrpc')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final jsonrpc = obj['jsonrpc'];
-        if (jsonrpc == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!(jsonrpc is String)) {
-          reporter.reportError('must be of type String');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      return true;
-    } else {
-      reporter.reportError('must be of type Message');
-      return false;
-    }
-  }
-
-  @override
-  bool operator ==(Object other) {
-    if (other is Message && other.runtimeType == Message) {
-      return clientRequestTime == other.clientRequestTime &&
-          jsonrpc == other.jsonrpc &&
-          true;
-    }
-    return false;
-  }
-
-  @override
-  int get hashCode => Object.hash(
-        clientRequestTime,
-        jsonrpc,
-      );
-
-  @override
-  String toString() => jsonEncoder.convert(toJson());
-}
-
 class MessageActionItem implements ToJsonable {
   static const jsonHandler = LspJsonHandler(
     MessageActionItem.canParse,
@@ -27218,137 +27119,6 @@ class NotebookDocumentSyncRegistrationOptions
   String toString() => jsonEncoder.convert(toJson());
 }
 
-class NotificationMessage implements Message, IncomingMessage, ToJsonable {
-  static const jsonHandler = LspJsonHandler(
-    NotificationMessage.canParse,
-    NotificationMessage.fromJson,
-  );
-
-  NotificationMessage({
-    this.clientRequestTime,
-    required this.jsonrpc,
-    required this.method,
-    this.params,
-  });
-  static NotificationMessage fromJson(Map<String, Object?> json) {
-    final clientRequestTimeJson = json['clientRequestTime'];
-    final clientRequestTime = clientRequestTimeJson as int?;
-    final jsonrpcJson = json['jsonrpc'];
-    final jsonrpc = jsonrpcJson as String;
-    final methodJson = json['method'];
-    final method = Method.fromJson(methodJson as String);
-    final paramsJson = json['params'];
-    final params = paramsJson;
-    return NotificationMessage(
-      clientRequestTime: clientRequestTime,
-      jsonrpc: jsonrpc,
-      method: method,
-      params: params,
-    );
-  }
-
-  final int? clientRequestTime;
-  final String jsonrpc;
-
-  /// The method to be invoked.
-  final Method method;
-
-  /// The notification's params.
-  final Object? params;
-
-  Map<String, Object?> toJson() {
-    var __result = <String, Object?>{};
-    if (clientRequestTime != null) {
-      __result['clientRequestTime'] = clientRequestTime;
-    }
-    __result['jsonrpc'] = jsonrpc;
-    __result['method'] = method.toJson();
-    if (params != null) {
-      __result['params'] = params;
-    }
-    return __result;
-  }
-
-  static bool canParse(Object? obj, LspJsonReporter reporter) {
-    if (obj is Map<String, Object?>) {
-      reporter.push('clientRequestTime');
-      try {
-        final clientRequestTime = obj['clientRequestTime'];
-        if (clientRequestTime != null && !(clientRequestTime is int)) {
-          reporter.reportError('must be of type int');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('jsonrpc');
-      try {
-        if (!obj.containsKey('jsonrpc')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final jsonrpc = obj['jsonrpc'];
-        if (jsonrpc == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!(jsonrpc is String)) {
-          reporter.reportError('must be of type String');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('method');
-      try {
-        if (!obj.containsKey('method')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final method = obj['method'];
-        if (method == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!(Method.canParse(method, reporter))) {
-          reporter.reportError('must be of type Method');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      return true;
-    } else {
-      reporter.reportError('must be of type NotificationMessage');
-      return false;
-    }
-  }
-
-  @override
-  bool operator ==(Object other) {
-    if (other is NotificationMessage &&
-        other.runtimeType == NotificationMessage) {
-      return clientRequestTime == other.clientRequestTime &&
-          jsonrpc == other.jsonrpc &&
-          method == other.method &&
-          params == other.params &&
-          true;
-    }
-    return false;
-  }
-
-  @override
-  int get hashCode => Object.hash(
-        clientRequestTime,
-        jsonrpc,
-        method,
-        params,
-      );
-
-  @override
-  String toString() => jsonEncoder.convert(toJson());
-}
-
 class OptionalVersionedTextDocumentIdentifier
     implements TextDocumentIdentifier, ToJsonable {
   static const jsonHandler = LspJsonHandler(
@@ -30843,168 +30613,6 @@ class RenameRegistrationOptions
   String toString() => jsonEncoder.convert(toJson());
 }
 
-class RequestMessage implements Message, IncomingMessage, ToJsonable {
-  static const jsonHandler = LspJsonHandler(
-    RequestMessage.canParse,
-    RequestMessage.fromJson,
-  );
-
-  RequestMessage({
-    this.clientRequestTime,
-    required this.id,
-    required this.jsonrpc,
-    required this.method,
-    this.params,
-  });
-  static RequestMessage fromJson(Map<String, Object?> json) {
-    final clientRequestTimeJson = json['clientRequestTime'];
-    final clientRequestTime = clientRequestTimeJson as int?;
-    final idJson = json['id'];
-    final id = idJson is int
-        ? Either2<int, String>.t1(idJson)
-        : (idJson is String
-            ? Either2<int, String>.t2(idJson)
-            : (throw '''$idJson was not one of (int, String)'''));
-    final jsonrpcJson = json['jsonrpc'];
-    final jsonrpc = jsonrpcJson as String;
-    final methodJson = json['method'];
-    final method = Method.fromJson(methodJson as String);
-    final paramsJson = json['params'];
-    final params = paramsJson;
-    return RequestMessage(
-      clientRequestTime: clientRequestTime,
-      id: id,
-      jsonrpc: jsonrpc,
-      method: method,
-      params: params,
-    );
-  }
-
-  final int? clientRequestTime;
-
-  /// The request id.
-  final Either2<int, String> id;
-  final String jsonrpc;
-
-  /// The method to be invoked.
-  final Method method;
-
-  /// The method's params.
-  final Object? params;
-
-  Map<String, Object?> toJson() {
-    var __result = <String, Object?>{};
-    if (clientRequestTime != null) {
-      __result['clientRequestTime'] = clientRequestTime;
-    }
-    __result['id'] = id;
-    __result['jsonrpc'] = jsonrpc;
-    __result['method'] = method.toJson();
-    if (params != null) {
-      __result['params'] = params;
-    }
-    return __result;
-  }
-
-  static bool canParse(Object? obj, LspJsonReporter reporter) {
-    if (obj is Map<String, Object?>) {
-      reporter.push('clientRequestTime');
-      try {
-        final clientRequestTime = obj['clientRequestTime'];
-        if (clientRequestTime != null && !(clientRequestTime is int)) {
-          reporter.reportError('must be of type int');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('id');
-      try {
-        if (!obj.containsKey('id')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final id = obj['id'];
-        if (id == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!((id is int || id is String))) {
-          reporter.reportError('must be of type Either2<int, String>');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('jsonrpc');
-      try {
-        if (!obj.containsKey('jsonrpc')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final jsonrpc = obj['jsonrpc'];
-        if (jsonrpc == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!(jsonrpc is String)) {
-          reporter.reportError('must be of type String');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('method');
-      try {
-        if (!obj.containsKey('method')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final method = obj['method'];
-        if (method == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!(Method.canParse(method, reporter))) {
-          reporter.reportError('must be of type Method');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      return true;
-    } else {
-      reporter.reportError('must be of type RequestMessage');
-      return false;
-    }
-  }
-
-  @override
-  bool operator ==(Object other) {
-    if (other is RequestMessage && other.runtimeType == RequestMessage) {
-      return clientRequestTime == other.clientRequestTime &&
-          id == other.id &&
-          jsonrpc == other.jsonrpc &&
-          method == other.method &&
-          params == other.params &&
-          true;
-    }
-    return false;
-  }
-
-  @override
-  int get hashCode => Object.hash(
-        clientRequestTime,
-        id,
-        jsonrpc,
-        method,
-        params,
-      );
-
-  @override
-  String toString() => jsonEncoder.convert(toJson());
-}
-
 class ResourceOperationKind implements ToJsonable {
   const ResourceOperationKind._(this._value);
   const ResourceOperationKind.fromJson(this._value);
@@ -31042,286 +30650,6 @@ class ResourceOperationKind implements ToJsonable {
       o is ResourceOperationKind && o._value == _value;
 }
 
-class ResponseError implements ToJsonable {
-  static const jsonHandler = LspJsonHandler(
-    ResponseError.canParse,
-    ResponseError.fromJson,
-  );
-
-  ResponseError({
-    required this.code,
-    this.data,
-    required this.message,
-  });
-  static ResponseError fromJson(Map<String, Object?> json) {
-    final codeJson = json['code'];
-    final code = ErrorCodes.fromJson(codeJson as int);
-    final dataJson = json['data'];
-    final data = dataJson as String?;
-    final messageJson = json['message'];
-    final message = messageJson as String;
-    return ResponseError(
-      code: code,
-      data: data,
-      message: message,
-    );
-  }
-
-  /// A number indicating the error type that occurred.
-  final ErrorCodes code;
-
-  /// A string that contains additional information about the error. Can be
-  /// omitted.
-  final String? data;
-
-  /// A string providing a short description of the error.
-  final String message;
-
-  Map<String, Object?> toJson() {
-    var __result = <String, Object?>{};
-    __result['code'] = code.toJson();
-    if (data != null) {
-      __result['data'] = data;
-    }
-    __result['message'] = message;
-    return __result;
-  }
-
-  static bool canParse(Object? obj, LspJsonReporter reporter) {
-    if (obj is Map<String, Object?>) {
-      reporter.push('code');
-      try {
-        if (!obj.containsKey('code')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final code = obj['code'];
-        if (code == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!(ErrorCodes.canParse(code, reporter))) {
-          reporter.reportError('must be of type ErrorCodes');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('data');
-      try {
-        final data = obj['data'];
-        if (data != null && !(data is String)) {
-          reporter.reportError('must be of type String');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('message');
-      try {
-        if (!obj.containsKey('message')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final message = obj['message'];
-        if (message == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!(message is String)) {
-          reporter.reportError('must be of type String');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      return true;
-    } else {
-      reporter.reportError('must be of type ResponseError');
-      return false;
-    }
-  }
-
-  @override
-  bool operator ==(Object other) {
-    if (other is ResponseError && other.runtimeType == ResponseError) {
-      return code == other.code &&
-          data == other.data &&
-          message == other.message &&
-          true;
-    }
-    return false;
-  }
-
-  @override
-  int get hashCode => Object.hash(
-        code,
-        data,
-        message,
-      );
-
-  @override
-  String toString() => jsonEncoder.convert(toJson());
-}
-
-class ResponseMessage implements Message, ToJsonable {
-  static const jsonHandler = LspJsonHandler(
-    ResponseMessage.canParse,
-    ResponseMessage.fromJson,
-  );
-
-  ResponseMessage({
-    this.clientRequestTime,
-    this.error,
-    this.id,
-    required this.jsonrpc,
-    this.result,
-  });
-  static ResponseMessage fromJson(Map<String, Object?> json) {
-    final clientRequestTimeJson = json['clientRequestTime'];
-    final clientRequestTime = clientRequestTimeJson as int?;
-    final errorJson = json['error'];
-    final error = errorJson != null
-        ? ResponseError.fromJson(errorJson as Map<String, Object?>)
-        : null;
-    final idJson = json['id'];
-    final id = idJson == null
-        ? null
-        : (idJson is int
-            ? Either2<int, String>.t1(idJson)
-            : (idJson is String
-                ? Either2<int, String>.t2(idJson)
-                : (throw '''$idJson was not one of (int, String)''')));
-    final jsonrpcJson = json['jsonrpc'];
-    final jsonrpc = jsonrpcJson as String;
-    final resultJson = json['result'];
-    final result = resultJson;
-    return ResponseMessage(
-      clientRequestTime: clientRequestTime,
-      error: error,
-      id: id,
-      jsonrpc: jsonrpc,
-      result: result,
-    );
-  }
-
-  final int? clientRequestTime;
-
-  /// The error object in case a request fails.
-  final ResponseError? error;
-
-  /// The request id.
-  final Either2<int, String>? id;
-  final String jsonrpc;
-
-  /// The result of a request. This member is REQUIRED on success. This member
-  /// MUST NOT exist if there was an error invoking the method.
-  final Object? result;
-
-  Map<String, Object?> toJson() {
-    var __result = <String, Object?>{};
-    if (clientRequestTime != null) {
-      __result['clientRequestTime'] = clientRequestTime;
-    }
-    __result['id'] = id;
-    __result['jsonrpc'] = jsonrpc;
-    if (error != null && result != null) {
-      throw 'result and error cannot both be set';
-    } else if (error != null) {
-      __result['error'] = error;
-    } else {
-      __result['result'] = result;
-    }
-    return __result;
-  }
-
-  static bool canParse(Object? obj, LspJsonReporter reporter) {
-    if (obj is Map<String, Object?>) {
-      reporter.push('clientRequestTime');
-      try {
-        final clientRequestTime = obj['clientRequestTime'];
-        if (clientRequestTime != null && !(clientRequestTime is int)) {
-          reporter.reportError('must be of type int');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('error');
-      try {
-        final error = obj['error'];
-        if (error != null && !(ResponseError.canParse(error, reporter))) {
-          reporter.reportError('must be of type ResponseError');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('id');
-      try {
-        if (!obj.containsKey('id')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final id = obj['id'];
-        if (id != null && !((id is int || id is String))) {
-          reporter.reportError('must be of type Either2<int, String>');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      reporter.push('jsonrpc');
-      try {
-        if (!obj.containsKey('jsonrpc')) {
-          reporter.reportError('must not be undefined');
-          return false;
-        }
-        final jsonrpc = obj['jsonrpc'];
-        if (jsonrpc == null) {
-          reporter.reportError('must not be null');
-          return false;
-        }
-        if (!(jsonrpc is String)) {
-          reporter.reportError('must be of type String');
-          return false;
-        }
-      } finally {
-        reporter.pop();
-      }
-      return true;
-    } else {
-      reporter.reportError('must be of type ResponseMessage');
-      return false;
-    }
-  }
-
-  @override
-  bool operator ==(Object other) {
-    if (other is ResponseMessage && other.runtimeType == ResponseMessage) {
-      return clientRequestTime == other.clientRequestTime &&
-          error == other.error &&
-          id == other.id &&
-          jsonrpc == other.jsonrpc &&
-          result == other.result &&
-          true;
-    }
-    return false;
-  }
-
-  @override
-  int get hashCode => Object.hash(
-        clientRequestTime,
-        error,
-        id,
-        jsonrpc,
-        result,
-      );
-
-  @override
-  String toString() => jsonEncoder.convert(toJson());
-}
-
 class SaveOptions implements ToJsonable {
   static const jsonHandler = LspJsonHandler(
     SaveOptions.canParse,
diff --git a/pkg/analysis_server/lib/lsp_protocol/protocol_special.dart b/pkg/analysis_server/lib/lsp_protocol/protocol_special.dart
index 5b4d3b1f15b..57cce1705a2 100644
--- a/pkg/analysis_server/lib/lsp_protocol/protocol_special.dart
+++ b/pkg/analysis_server/lib/lsp_protocol/protocol_special.dart
@@ -8,6 +8,8 @@ import 'package:analysis_server/lsp_protocol/protocol_generated.dart';
 import 'package:analysis_server/src/lsp/json_parsing.dart';
 import 'package:analysis_server/src/protocol/protocol_internal.dart';
 
+import 'protocol_custom_generated.dart';
+
 const jsonRpcVersion = '2.0';
 
 const NullJsonHandler = LspJsonHandler<Null>(_alwaysTrue, _alwaysNull);
@@ -264,14 +266,6 @@ class ErrorOr<T> extends Either2<ResponseError, T> {
   }
 }
 
-/// A base class containing the fields common to RequestMessage and
-/// NotificationMessage to simplify handling.
-abstract class IncomingMessage {
-  int? get clientRequestTime;
-  Method get method;
-  dynamic get params;
-}
-
 /// A helper to allow handlers to declare both a JSON validation function and
 /// parse function.
 class LspJsonHandler<T> {
diff --git a/pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart b/pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart
index bbcd39bbb9b..dbc283220cf 100644
--- a/pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart
+++ b/pkg/analysis_server/lib/src/lsp/lsp_analysis_server.dart
@@ -350,21 +350,19 @@ class LspAnalysisServer extends AbstractAnalysisServer {
         if (message is ResponseMessage) {
           handleClientResponse(message);
         } else if (message is IncomingMessage) {
-          final incomingMessage = message as IncomingMessage;
-
           // Record performance information for the request.
           final performance = OperationPerformanceImpl('<root>');
           await performance.runAsync('request', (performance) async {
             final requestPerformance = RequestPerformance(
-              operation: incomingMessage.method.toString(),
+              operation: message.method.toString(),
               performance: performance,
-              requestLatency: incomingMessage.timeSinceRequest,
+              requestLatency: message.timeSinceRequest,
             );
             recentPerformance.requests.add(requestPerformance);
 
             final messageInfo = MessageInfo(
               performance: performance,
-              timeSinceRequest: incomingMessage.timeSinceRequest,
+              timeSinceRequest: message.timeSinceRequest,
             );
 
             if (message is RequestMessage) {
diff --git a/pkg/analysis_server/tool/lsp_spec/codegen_dart.dart b/pkg/analysis_server/tool/lsp_spec/codegen_dart.dart
index d01feeafa36..3ed92285505 100644
--- a/pkg/analysis_server/tool/lsp_spec/codegen_dart.dart
+++ b/pkg/analysis_server/tool/lsp_spec/codegen_dart.dart
@@ -4,7 +4,6 @@
 
 import 'package:dart_style/dart_style.dart';
 
-import 'typescript.dart';
 import 'typescript_parser.dart';
 
 final formatter = DartFormatter();
@@ -786,7 +785,6 @@ void _writeInterface(IndentableStringBuffer buffer, Interface interface) {
   buffer.writeIndented('class ${interface.nameWithTypeArgs} ');
   final allBaseTypes =
       interface.baseTypes.map((t) => t.dartTypeWithTypeArgs).toList();
-  allBaseTypes.addAll(getSpecialBaseTypes(interface));
   allBaseTypes.add('ToJsonable');
   if (allBaseTypes.isNotEmpty) {
     buffer.writeIndented('implements ${allBaseTypes.join(', ')} ');
diff --git a/pkg/analysis_server/tool/lsp_spec/generate_all.dart b/pkg/analysis_server/tool/lsp_spec/generate_all.dart
index 57b545bfe85..92e5880935e 100644
--- a/pkg/analysis_server/tool/lsp_spec/generate_all.dart
+++ b/pkg/analysis_server/tool/lsp_spec/generate_all.dart
@@ -196,15 +196,23 @@ List<AstNode> getCustomClasses() {
 
   Field field(
     String name, {
+    String? comment,
     required String type,
     bool array = false,
     bool canBeUndefined = false,
   }) {
-    var fieldType =
+    final fieldType =
         array ? ArrayType(Type.identifier(type)) : Type.identifier(type);
+    final commentNode =
+        comment != null ? Comment(Token(TokenType.COMMENT, comment)) : null;
 
-    return Field(null, Token.identifier(name), fieldType,
-        allowsNull: false, allowsUndefined: canBeUndefined);
+    return Field(
+      commentNode,
+      Token.identifier(name),
+      fieldType,
+      allowsNull: false,
+      allowsUndefined: canBeUndefined,
+    );
   }
 
   final customTypes = <AstNode>[
@@ -218,6 +226,72 @@ List<AstNode> getCustomClasses() {
       Token.identifier('LSPObject'),
       Type.Any,
     ),
+    interface('Message', [
+      field('jsonrpc', type: 'string'),
+      field('clientRequestTime', type: 'int', canBeUndefined: true),
+    ]),
+    interface(
+      'IncomingMessage',
+      [
+        field('method', type: 'Method'),
+        field('params', type: 'LSPAny', canBeUndefined: true),
+      ],
+      baseType: 'Message',
+    ),
+    interface(
+      'RequestMessage',
+      [
+        Field(
+          null,
+          Token.identifier('id'),
+          UnionType([Type.identifier('int'), Type.identifier('string')]),
+          allowsNull: false,
+          allowsUndefined: false,
+        )
+      ],
+      baseType: 'IncomingMessage',
+    ),
+    interface(
+      'NotificationMessage',
+      [],
+      baseType: 'IncomingMessage',
+    ),
+    interface(
+      'ResponseMessage',
+      [
+        Field(
+          null,
+          Token.identifier('id'),
+          UnionType([Type.identifier('int'), Type.identifier('string')]),
+          allowsNull: true,
+          allowsUndefined: false,
+        ),
+        field('result', type: 'LSPAny', canBeUndefined: true),
+        field('error', type: 'ResponseError', canBeUndefined: true),
+      ],
+      baseType: 'Message',
+    ),
+    interface(
+      'ResponseError',
+      [
+        field('code', type: 'ErrorCodes'),
+        field('message', type: 'string'),
+        // This is Object? normally, but since this class can be serialised
+        // we will crash if it data is set to something that can't be converted to
+        // JSON (for ex. Uri) so this forces anyone setting this to convert to a
+        // String.
+        field(
+          'data',
+          type: 'string',
+          canBeUndefined: true,
+          comment:
+              'A string that contains additional information about the error. '
+              'Can be omitted.',
+        ),
+      ],
+    ),
+    TypeAlias(null, Token.identifier('DocumentUri'), Type.identifier('string')),
+
     interface('DartDiagnosticServer', [field('port', type: 'int')]),
     interface('AnalyzerStatusParams', [field('isAnalyzing', type: 'boolean')]),
     interface('PublishClosingLabelsParams', [
@@ -326,34 +400,6 @@ List<AstNode> getCustomClasses() {
   return customTypes;
 }
 
-/// Gets additional custom fields to be added to LSP Spec classes.
-///
-/// Non-standard fields should generally be avoided and must always allow
-/// undefined.
-List<Field> getCustomFields(String interfaceName) {
-  final additionalFields = <String, List<Field>>{
-    // Allow clients to pass a "clientRequestTime" against any incomine message
-    // so that we can capture latency information for requests for performance
-    // measurements.
-    'Message': [
-      Field(
-        null,
-        Token.identifier('clientRequestTime'),
-        Type.identifier('int'),
-        allowsNull: false,
-        allowsUndefined: true,
-      ),
-    ],
-  };
-
-  final fields = additionalFields[interfaceName] ?? [];
-  assert(
-    fields.every((field) => field.allowsUndefined),
-    'Any additional non-standard LSP field must allow undefined',
-  );
-  return fields;
-}
-
 Future<List<AstNode>> getSpecClasses(ArgResults args) async {
   var download = args[argDownload] as bool;
   if (download) {
@@ -366,7 +412,6 @@ Future<List<AstNode>> getSpecClasses(ArgResults args) async {
       .map(parseString)
       .expand((f) => f)
       .where(includeTypeDefinitionInOutput)
-      .map(withCustomFields)
       .toList();
 
   // Generate an enum for all of the request methods to avoid strings.
@@ -417,26 +462,6 @@ bool shouldIncludeScriptBlock(String input) {
   return true;
 }
 
-/// Returns [node] with any additional custom fields.
-AstNode withCustomFields(AstNode node) {
-  if (node is! Interface) {
-    return node;
-  }
-
-  final customFields = getCustomFields(node.name);
-  if (customFields.isEmpty) {
-    return node;
-  }
-
-  return Interface(
-    node.commentNode,
-    node.nameToken,
-    node.typeArgs,
-    node.baseTypes,
-    [...node.members, ...customFields],
-  );
-}
-
 /// Fetches and in-lines any includes that appear in [spec] in the form
 /// `{% include_relative types/uri.md %}`.
 Future<String> _fetchIncludes(String spec, Uri baseUri) async {
diff --git a/pkg/analysis_server/tool/lsp_spec/typescript.dart b/pkg/analysis_server/tool/lsp_spec/typescript.dart
index 002772477de..0ca98c374e5 100644
--- a/pkg/analysis_server/tool/lsp_spec/typescript.dart
+++ b/pkg/analysis_server/tool/lsp_spec/typescript.dart
@@ -43,21 +43,6 @@ String cleanComment(String comment) {
   return comment.trim();
 }
 
-/// Improves comments in generated code to support where types may have been
-/// altered (for ex. with [getImprovedType] above).
-String? getImprovedComment(String interfaceName, String fieldName) {
-  const improvedComments = <String, Map<String, String>>{
-    'ResponseError': {
-      'data':
-          '// A string that contains additional information about the error. Can be omitted.',
-    },
-  };
-
-  final interface = improvedComments[interfaceName];
-
-  return interface != null ? interface[fieldName] : null;
-}
-
 /// Improves types in generated code, including:
 ///
 /// - Fixes up some enum types that are not as specific as they could be in the
@@ -96,22 +81,6 @@ String? getImprovedType(String interfaceName, String? fieldName) {
     'FoldingRange': {
       'kind': 'FoldingRangeKind',
     },
-    'ResponseError': {
-      'code': 'ErrorCodes',
-      // This is Object? normally, but since this class can be serialised
-      // we will crash if it data is set to something that can't be converted to
-      // JSON (for ex. Uri) so this forces anyone setting this to convert to a
-      // String.
-      'data': 'String',
-    },
-    'NotificationMessage': {
-      'method': 'Method',
-      'params': 'object',
-    },
-    'RequestMessage': {
-      'method': 'Method',
-      'params': 'object',
-    },
     'SymbolInformation': {
       'kind': 'SymbolKind',
     },
@@ -134,26 +103,30 @@ String? getImprovedType(String interfaceName, String? fieldName) {
   return interface != null ? interface[fieldName] : null;
 }
 
-List<String> getSpecialBaseTypes(Interface interface) {
-  if (interface.name == 'RequestMessage' ||
-      interface.name == 'NotificationMessage') {
-    return ['IncomingMessage'];
-  } else {
-    return [];
-  }
-}
-
 /// Removes types that are in the spec that we don't want to emit.
 bool includeTypeDefinitionInOutput(AstNode node) {
-  // InitializeError is not used for v3.0 (Feb 2017) and by dropping it we don't
-  // have to handle any cases where both a namespace and interfaces are declared
-  // with the same name.
-  return node.name != 'InitializeError' &&
-      // We don't use `InitializeErrorCodes` as it contains only one error code
-      // that has been deprecated and we've never used.
-      node.name != 'InitializeErrorCodes' &&
-      // We don't emit MarkedString because it gets mapped to a simple String
-      // when getting the .dartType for it.
-      // .startsWith() because there are inline types that will be generated.
-      !node.name.startsWith('MarkedString');
+  const ignoredTypes = {
+    // InitializeError is not used for v3.0 (Feb 2017) and by dropping it we don't
+    // have to handle any cases where both a namespace and interfaces are declared
+    // with the same name.
+    'InitializeError',
+    // We don't use `InitializeErrorCodes` as it contains only one error code
+    // that has been deprecated and we've never used.
+    'InitializeErrorCodes',
+    // Handled in custom classes now in preperation for JSON meta model which
+    // does not specify them.
+    'Message',
+    'RequestMessage',
+    'NotificationMessage',
+    'ResponseMessage',
+    'ResponseError',
+  };
+  const ignoredPrefixes = {
+    // We don't emit MarkedString because it gets mapped to a simple String
+    // when getting the .dartType for it.
+    'MarkedString'
+  };
+  final shouldIgnore = ignoredTypes.contains(node.name) ||
+      ignoredPrefixes.any((ignore) => node.name.startsWith(ignore));
+  return !shouldIgnore;
 }
diff --git a/pkg/analysis_server/tool/lsp_spec/typescript_parser.dart b/pkg/analysis_server/tool/lsp_spec/typescript_parser.dart
index d2b2eabc944..d0744602df3 100644
--- a/pkg/analysis_server/tool/lsp_spec/typescript_parser.dart
+++ b/pkg/analysis_server/tool/lsp_spec/typescript_parser.dart
@@ -378,12 +378,6 @@ class Parser {
     type = _type(containerName, name.lexeme,
         includeUndefined: canBeUndefined, improveTypes: true);
 
-    // Overwrite comment if we have an improved one.
-    final improvedComment = getImprovedComment(containerName, name.lexeme);
-    leadingComment = improvedComment != null
-        ? Comment(Token(TokenType.COMMENT, improvedComment))
-        : leadingComment;
-
     // Some fields have weird comments like this in the spec:
     //     {@link MessageType}
     // These seem to be the correct type of the field, while the field is