[anaysis_server] Move ErrorOr class from LSP package to analysis_server

ErrorOr is not related to (or used by) the spec or generated spec classes. It's a utility class for the server implementations of LSP handlers.

I'd like to extend this class and add some extensions (that require access to private fields) and don't feel it belongs in `package:language_server_protocol`.

(note: `package:language_server_protocol` is not published so I believe removing it from there is not a breaking change)

Change-Id: I06799b18d61d123364711a549231134c792e70e2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/361140
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server/lib/src/handler/legacy/lsp_over_legacy_handler.dart

@@ -8,6 +8,7 @@ import 'package:analysis_server/protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/handler/legacy/legacy_handler.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handler_states.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart' as lsp;
 import 'package:analyzer/dart/analysis/session.dart';

pkg/analysis_server/lib/src/lsp/error_or.dart

@@ -0,0 +1,74 @@
+// Copyright (c) 2024, 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 'package:analysis_server/lsp_protocol/protocol.dart';
+
+ErrorOr<R> cancelled<R>() =>
+    error(ErrorCodes.RequestCancelled, 'Request was cancelled');
+
+ErrorOr<R> error<R>(ErrorCodes code, String message, [String? data]) =>
+    ErrorOr<R>.error(ResponseError(code: code, message: message, data: data));
+
+ErrorOr<R> failure<R>(ErrorOr<dynamic> error) => ErrorOr<R>.error(error.error);
+
+ErrorOr<R> success<R>(R t) => ErrorOr<R>.success(t);
+
+/// A specialised version of [Either2] for working with results or errors in
+/// LSP handlers.
+///
+/// Contains a helpers to assist in chaining operations while propagating errors.
+class ErrorOr<T> extends Either2<ResponseError, T> {
+  ErrorOr.error(super.error) : super.t1();
+
+  ErrorOr.success(super.result) : super.t2();
+
+  /// Returns the error or throws if object is not an error. Check [isError]
+  /// before accessing [error].
+  ResponseError get error {
+    return map((error) => error, (_) => throw 'Value is not an error');
+  }
+
+  /// Returns true if this object is an error, false if it is a result. Prefer
+  /// [mapResult] instead of checking this flag if [errors] will simply be
+  /// propagated as-is.
+  bool get isError => map((error) => true, (_) => false);
+
+  /// Returns the result or throws if this object is an error. Check [isError]
+  /// before accessing [result]. It is valid for this to return null is the
+  /// object does not represent an error but the resulting value was null.
+  T get result {
+    return map((_) => throw 'Value is not a result', (result) => result);
+  }
+
+  /// Returns the result or `null` if this object is an error.
+  T? get resultOrNull {
+    return map((_) => null, (result) => result);
+  }
+
+  /// If this object is a result, maps [result] through [f], otherwise returns
+  /// a new error object representing [error].
+  FutureOr<ErrorOr<N>> mapResult<N>(FutureOr<ErrorOr<N>> Function(T) f) {
+    return isError
+        // Re-wrap the error using our new type arg
+        ? ErrorOr<N>.error(error)
+        // Otherwise call the map function
+        : f(result);
+  }
+
+  /// Converts a [List<ErrorOr<T>>] into an [ErrorOr<List<T>>]. If any of the
+  /// items represents an error, that error will be returned. Otherwise, the
+  /// list of results will be returned in a success response.
+  static ErrorOr<List<T>> all<T>(Iterable<ErrorOr<T>> items) {
+    final results = <T>[];
+    for (final item in items) {
+      if (item.isError) {
+        return failure(item);
+      }
+      results.add(item.result);
+    }
+    return success(results);
+  }
+}

pkg/analysis_server/lib/src/lsp/handlers/code_lens/abstract_code_lens_provider.dart

@@ -6,6 +6,7 @@ import 'package:analysis_server/lsp_protocol/protocol.dart'
     hide Declaration, Element;
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analyzer/dart/element/element.dart';

pkg/analysis_server/lib/src/lsp/handlers/code_lens/augmentations.dart

@@ -5,6 +5,7 @@
 import 'package:analysis_server/lsp_protocol/protocol.dart'
     hide Declaration, Element;
 import 'package:analysis_server/src/lsp/client_configuration.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/code_lens/abstract_code_lens_provider.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/abstract_refactor.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/simple_edit_handler.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/progress.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/fix_all.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/simple_edit_handler.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/lsp_analysis_server.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/fix_all_in_workspace.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/simple_edit_handler.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/log_action.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/progress.dart';
 

pkg/analysis_server/lib/src/lsp/handlers/commands/organize_imports.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/simple_edit_handler.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/progress.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/perform_refactor.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/abstract_refactor.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/refactor_command_handler.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/simple_edit_handler.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/send_workspace_edit.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/simple_edit_handler.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/progress.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/simple_edit_handler.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/source_edits.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/sort_members.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/simple_edit_handler.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/progress.dart';

pkg/analysis_server/lib/src/lsp/handlers/commands/validate_refactor.dart

@@ -5,6 +5,7 @@
 import 'dart:async';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/abstract_refactor.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/progress.dart';

pkg/analysis_server/lib/src/lsp/handlers/custom/abstract_go_to.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart' hide Element;
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analyzer/dart/element/element.dart';

pkg/analysis_server/lib/src/lsp/handlers/custom/handler_diagnostic_server.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 
 class DiagnosticServerHandler

pkg/analysis_server/lib/src/lsp/handlers/custom/handler_reanalyze.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 
 class ReanalyzeHandler extends LspMessageHandler<void, void> {

pkg/analysis_server/lib/src/lsp/handlers/handler_call_hierarchy.dart

@@ -7,6 +7,7 @@ import 'dart:async';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/computer/computer_call_hierarchy.dart'
     as call_hierarchy;
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_cancel_request.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 
 class CancelRequestHandler extends SharedMessageHandler<CancelParams, void> {

pkg/analysis_server/lib/src/lsp/handlers/handler_change_workspace_folders.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';
 

pkg/analysis_server/lib/src/lsp/handlers/handler_code_actions.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/code_actions/abstract_code_actions_producer.dart';
 import 'package:analysis_server/src/lsp/handlers/code_actions/analysis_options.dart';
 import 'package:analysis_server/src/lsp/handlers/code_actions/dart.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_code_lens.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/code_lens/abstract_code_lens_provider.dart';
 import 'package:analysis_server/src/lsp/handlers/code_lens/augmentations.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_completion.dart

@@ -8,6 +8,7 @@ import 'package:analysis_server/lsp_protocol/protocol.dart' hide Declaration;
 import 'package:analysis_server/src/computer/computer_hover.dart';
 import 'package:analysis_server/src/lsp/client_capabilities.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_completion_resolve.dart

@@ -5,6 +5,7 @@
 import 'package:analysis_server/lsp_protocol/protocol.dart' hide Element;
 import 'package:analysis_server/src/computer/computer_hover.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analyzer/dart/analysis/results.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_dart_text_document_content_provider.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';
 import 'package:analyzer/dart/analysis/results.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_definition.dart

@@ -5,6 +5,7 @@
 import 'package:analysis_server/lsp_protocol/protocol.dart' hide Element;
 import 'package:analysis_server/protocol/protocol_generated.dart'
     hide AnalysisGetNavigationParams;
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_document_color.dart

@@ -5,6 +5,7 @@
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/computer/computer_color.dart'
     show ColorComputer, ColorReference;
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_document_color_presentation.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/utilities/flutter.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_document_highlights.dart

@@ -5,6 +5,7 @@
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/domains/analysis/occurrences.dart';
 import 'package:analysis_server/src/domains/analysis/occurrences_dart.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_document_link.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart' hide Element;
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_document_symbols.dart

@@ -5,6 +5,7 @@
 import 'package:analysis_server/lsp_protocol/protocol.dart' hide Outline;
 import 'package:analysis_server/src/computer/computer_outline.dart';
 import 'package:analysis_server/src/lsp/client_capabilities.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_execute_command.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/fix_all.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/fix_all_in_workspace.dart';
 import 'package:analysis_server/src/lsp/handlers/commands/log_action.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_exit.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 
 class ExitMessageHandler extends LspMessageHandler<void, void> {

pkg/analysis_server/lib/src/lsp/handlers/handler_folding.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/computer/computer_folding.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_format_on_type.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_format_range.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_formatting.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_hover.dart

@@ -6,6 +6,7 @@ import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/computer/computer_hover.dart';
 import 'package:analysis_server/src/lsp/dartdoc.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_implementation.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart'
     hide TypeHierarchyItem, Element;
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_initialize.dart

@@ -5,6 +5,7 @@
 import 'dart:io';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handler_states.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 

pkg/analysis_server/lib/src/lsp/handlers/handler_initialized.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handler_states.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 

pkg/analysis_server/lib/src/lsp/handlers/handler_inlay_hint.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/computer/computer_inlay_hint.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_references.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_reject.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 
 /// A [MessageHandler] that rejects specific types of messages with a given

pkg/analysis_server/lib/src/lsp/handlers/handler_rename.dart

@@ -6,6 +6,7 @@ import 'package:analysis_server/lsp_protocol/protocol.dart' hide MessageType;
 import 'package:analysis_server/src/analysis_server.dart' show MessageType;
 import 'package:analysis_server/src/lsp/client_configuration.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_selection_range.dart

@@ -5,6 +5,7 @@
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/computer/computer_selection_ranges.dart'
     hide SelectionRange;
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_semantic_tokens.dart

@@ -7,6 +7,7 @@ import 'dart:async';
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/computer/computer_highlights.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_shutdown.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handler_states.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 

pkg/analysis_server/lib/src/lsp/handlers/handler_signature_help.dart

@@ -6,6 +6,7 @@ import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/computer/computer_signature.dart';
 import 'package:analysis_server/src/computer/computer_type_arguments_signature.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_states.dart

@@ -7,6 +7,7 @@ import 'dart:async';
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/custom/handler_augmentation.dart';
 import 'package:analysis_server/src/lsp/handlers/custom/handler_augmented.dart';
 import 'package:analysis_server/src/lsp/handlers/custom/handler_diagnostic_server.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_text_document_changes.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';
 import 'package:analysis_server/src/lsp/source_edits.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_type_definition.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_type_hierarchy.dart

@@ -8,6 +8,7 @@ import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/computer/computer_lazy_type_hierarchy.dart'
     as type_hierarchy;
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_will_rename_files.dart

@@ -4,6 +4,7 @@
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handler_workspace_configuration.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';
 

pkg/analysis_server/lib/src/lsp/handlers/handler_workspace_symbols.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/lsp/registration/feature_registration.dart';

pkg/analysis_server/lib/src/lsp/handlers/handlers.dart

@@ -7,6 +7,7 @@ import 'dart:async';
 import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handler_cancel_request.dart';
 import 'package:analysis_server/src/lsp/handlers/handler_reject.dart';
 import 'package:analysis_server/src/lsp/lsp_analysis_server.dart';

pkg/analysis_server/lib/src/lsp/mapping.dart

@@ -11,6 +11,7 @@ import 'package:analysis_server/src/lsp/client_capabilities.dart';
 import 'package:analysis_server/src/lsp/constants.dart' as lsp;
 import 'package:analysis_server/src/lsp/constants.dart';
 import 'package:analysis_server/src/lsp/dartdoc.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/lsp_analysis_server.dart' as lsp;
 import 'package:analysis_server/src/lsp/snippets.dart';
 import 'package:analysis_server/src/lsp/source_edits.dart';

pkg/analysis_server/lib/src/lsp/source_edits.dart

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/mapping.dart';
 import 'package:analysis_server/src/protocol_server.dart' as server
     show SourceEdit;

pkg/analysis_server/test/lsp/source_edits_test.dart

@@ -5,6 +5,7 @@
 import 'dart:convert';
 
 import 'package:analysis_server/lsp_protocol/protocol.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/source_edits.dart';
 import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';

pkg/analysis_server/test/services/user_prompts/dart_fix_prompt_manager_test.dart

@@ -8,6 +8,7 @@ import 'package:analysis_server/lsp_protocol/protocol.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/lsp/client_capabilities.dart';
 import 'package:analysis_server/src/lsp/constants.dart';
+import 'package:analysis_server/src/lsp/error_or.dart';
 import 'package:analysis_server/src/lsp/handlers/handler_execute_command.dart';
 import 'package:analysis_server/src/lsp/handlers/handlers.dart';
 import 'package:analysis_server/src/lsp/lsp_analysis_server.dart';

third_party/pkg/language_server_protocol/lib/protocol_special.dart

@@ -2,8 +2,6 @@
 // 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:collection/collection.dart';
 import 'package:language_server_protocol/json_parsing.dart';
 import 'package:language_server_protocol/protocol_custom_generated.dart';
@@ -13,14 +11,6 @@ const jsonRpcVersion = '2.0';
 
 const NullJsonHandler = LspJsonHandler<void>(_alwaysTrue, _alwaysNull);
 
-ErrorOr<R> cancelled<R>() =>
-    error(ErrorCodes.RequestCancelled, 'Request was cancelled', null);
-
-ErrorOr<R> error<R>(ErrorCodes code, String message, [String? data]) =>
-    ErrorOr<R>.error(ResponseError(code: code, message: message, data: data));
-
-ErrorOr<R> failure<R>(ErrorOr<dynamic> error) => ErrorOr<R>.error(error.error);
-
 /// Returns if two objects are equal, recursively checking items in
 /// Maps/Lists.
 bool lspEquals(dynamic obj1, dynamic obj2) {
@@ -41,8 +31,6 @@ Object? specToJson(Object? obj) {
   }
 }
 
-ErrorOr<R> success<R>(R t) => ErrorOr<R>.success(t);
-
 void _alwaysNull(_, [__]) {}
 
 bool _alwaysTrue(_, [__]) => true;
@@ -209,59 +197,6 @@ class Either4<T1, T2, T3, T4> implements ToJsonable {
       map((t) => t == o, (t) => t == o, (t) => t == o, (t) => t == o);
 }
 
-class ErrorOr<T> extends Either2<ResponseError, T> {
-  ErrorOr.error(super.error) : super.t1();
-
-  ErrorOr.success(super.result) : super.t2();
-
-  /// Returns the error or throws if object is not an error. Check [isError]
-  /// before accessing [error].
-  ResponseError get error {
-    return _which == 1 ? _t1 as ResponseError : (throw 'Value is not an error');
-  }
-
-  /// Returns true if this object is an error, false if it is a result. Prefer
-  /// [mapResult] instead of checking this flag if [errors] will simply be
-  /// propagated as-is.
-  bool get isError => _which == 1;
-
-  /// Returns the result or throws if this object is an error. Check [isError]
-  /// before accessing [result]. It is valid for this to return null is the
-  /// object does not represent an error but the resulting value was null.
-  T get result {
-    return _which == 2 ? _t2 as T : (throw 'Value is not a result');
-  }
-
-  /// Returns the result or `null` if this object is an error.
-  T? get resultOrNull {
-    return _which == 2 ? _t2 as T : null;
-  }
-
-  /// If this object is a result, maps [result] through [f], otherwise returns
-  /// a new error object representing [error].
-  FutureOr<ErrorOr<N>> mapResult<N>(FutureOr<ErrorOr<N>> Function(T) f) {
-    return isError
-        // Re-wrap the error using our new type arg
-        ? ErrorOr<N>.error(error)
-        // Otherwise call the map function
-        : f(result);
-  }
-
-  /// Converts a [List<ErrorOr<T>>] into an [ErrorOr<List<T>>]. If any of the
-  /// items represents an error, that error will be returned. Otherwise, the
-  /// list of results will be returned in a success response.
-  static ErrorOr<List<T>> all<T>(Iterable<ErrorOr<T>> items) {
-    final results = <T>[];
-    for (final item in items) {
-      if (item.isError) {
-        return failure(item);
-      }
-      results.add(item.result);
-    }
-    return success(results);
-  }
-}
-
 /// A helper to allow handlers to declare both a JSON validation function and
 /// parse function.
 class LspJsonHandler<T> {