[messages] Mark some messages as "pseudoShared".

A `pseudoShared` message is a front-end message that is generated by
code in the `_fe_analyzer_shared` package, and has a corresponding
analyzer message, but the error messages are not truly shared; the
analyzer message may have different text or parameters.

In the long term I plan to fully share all of these messages. However,
in the short term, this will allow the logic for front end error code
generation to be cleaned up, so that only messages that are truly
shared, or truly needed by `package:_fe_analyzer_shared` are emitted
to `pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart`.

Change-Id: I6a6a6964bbb146afd41c39ab73b4bc8bbcc5b81c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/449607
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

pkg/analyzer_utilities/lib/messages.dart

@@ -2,6 +2,9 @@
 // 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.
 
+/// @docImport 'package:analyzer/src/fasta/error_converter.dart';
+library;
+
 import 'dart:convert';
 import 'dart:io';
 
@@ -800,7 +803,21 @@ enum ErrorCodeParameterType {
 /// In-memory representation of error code information obtained from the file
 /// `pkg/front_end/messages.yaml`.
 class FrontEndErrorCodeInfo extends CfeStyleErrorCodeInfo {
-  FrontEndErrorCodeInfo.fromYaml(super.yaml) : super.fromYaml() {
+  /// Whether the error code contains a `pseudoShared: true` property in
+  /// `pkg/front_end/messages.yaml`.
+  ///
+  /// Messages with this property set are not shared; they have separately
+  /// declared analyzer and CFE codes. However, they are reported by code
+  /// defined in `pkg/_fe_analyzer_shared` using the CFE error reporting
+  /// mechanism. When running under the analyzer, they are then translated
+  /// into the associated analyzer error using [FastaErrorReporter].
+  // TODO(paulberry): migrate all pseudo-shared error codes to shared error
+  // codes.
+  final bool pseudoShared;
+
+  FrontEndErrorCodeInfo.fromYaml(super.yaml)
+    : pseudoShared = (yaml['pseudoShared'] as bool?) ?? false,
+      super.fromYaml() {
     if (index != null) {
       throw StateError('Non-shared messages must not have an index');
     }