[messages] Add package getter to MessageWithAnalyzerCode.

Adds the abstract getter `MessageWithAnalyzerCode.package` (and
implementations thereof). This returns the package into which this
error code will be generated.

Also adds a check to the `DiagnosticTables._` constructor to verify
that the values returned by this getter are the same as the values
returned by
`MessageWithAnalyzerCode.diagnosticClassInfo.file.package`, and
changes the code generation logic to use the former instead of the
latter where possible.

This paves the way for a follow-up CL that will remove
`MessageWithAnalyzerCode.diagnosticClassInfo`, as part of a larger
effort to remove the generated `DiagnosticCode`-derived classes
entirely.

Change-Id: I6a6a6964b03e53867f7dc7f7307e8e218c080b6c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/462161
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

Author: stereotype441

pkg/analyzer_utilities/lib/analyzer_messages.dart

@@ -187,6 +187,7 @@ const transformSetErrorCodeFile = GeneratedDiagnosticFile(
 /// Decoded messages from the analysis server's `messages.yaml` file.
 final List<AnalyzerMessage> analysisServerMessages = decodeAnalyzerMessagesYaml(
   analysisServerPkgPath,
+  package: AnalyzerDiagnosticPackage.analysisServer,
 );
 
 /// The path to the `analysis_server` package.
@@ -197,6 +198,7 @@ final String analysisServerPkgPath = normalize(
 /// Decoded messages from the analyzer's `messages.yaml` file.
 final List<AnalyzerMessage> analyzerMessages = decodeAnalyzerMessagesYaml(
   analyzerPkgPath,
+  package: AnalyzerDiagnosticPackage.analyzer,
 );
 
 /// The path to the `analyzer` package.
@@ -211,6 +213,7 @@ final String linterPkgPath = normalize(join(pkg_root.packageRoot, 'linter'));
 final List<AnalyzerMessage> lintMessages = decodeAnalyzerMessagesYaml(
   linterPkgPath,
   allowLinterKeys: true,
+  package: AnalyzerDiagnosticPackage.linter,
 );
 
 /// Decodes a YAML object (in analyzer style `messages.yaml` format) into a list
@@ -221,6 +224,7 @@ final List<AnalyzerMessage> lintMessages = decodeAnalyzerMessagesYaml(
 List<AnalyzerMessage> decodeAnalyzerMessagesYaml(
   String packagePath, {
   bool allowLinterKeys = false,
+  required AnalyzerDiagnosticPackage package,
 }) {
   var path = join(packagePath, 'messages.yaml');
   var yaml = loadYamlNode(
@@ -277,6 +281,7 @@ List<AnalyzerMessage> decodeAnalyzerMessagesYaml(
             messageYaml,
             analyzerCode: analyzerCode,
             allowLinterKeys: allowLinterKeys,
+            package: package,
           );
         },
       );
@@ -357,6 +362,7 @@ class AliasMessage extends AnalyzerMessage {
     required this.aliasFor,
     required super.analyzerCode,
     required super.allowLinterKeys,
+    required super.package,
   }) : super._();
 
   String get aliasForClass => aliasFor.split('.').first;
@@ -471,23 +477,29 @@ class AnalyzerMessage extends Message with MessageWithAnalyzerCode {
   @override
   final bool hasPublishedDocs;
 
+  @override
+  final AnalyzerDiagnosticPackage package;
+
   factory AnalyzerMessage(
     MessageYaml messageYaml, {
     required AnalyzerCode analyzerCode,
     required bool allowLinterKeys,
+    required AnalyzerDiagnosticPackage package,
   }) {
     if (messageYaml.getOptionalString('aliasFor') case var aliasFor?) {
       return AliasMessage(
         messageYaml,
         aliasFor: aliasFor,
         analyzerCode: analyzerCode,
         allowLinterKeys: allowLinterKeys,
+        package: package,
       );
     } else {
       return AnalyzerMessage._(
         messageYaml,
         analyzerCode: analyzerCode,
         allowLinterKeys: allowLinterKeys,
+        package: package,
       );
     }
   }
@@ -496,6 +508,7 @@ class AnalyzerMessage extends Message with MessageWithAnalyzerCode {
     MessageYaml messageYaml, {
     required this.analyzerCode,
     required bool allowLinterKeys,
+    required this.package,
   }) : hasPublishedDocs = messageYaml.getBool('hasPublishedDocs'),
        super(messageYaml) {
     // Ignore extra keys related to analyzer example-based tests.
@@ -651,6 +664,9 @@ mixin MessageWithAnalyzerCode on Message {
   /// `null` if the YAML doesn't contain this information.
   bool get hasPublishedDocs;
 
+  /// The package into which this error code will be generated.
+  AnalyzerDiagnosticPackage get package;
+
   void outputConstantHeader(StringSink out) {
     out.write(toAnalyzerComments(indent: '  '));
     if (deprecatedMessage != null) {

pkg/analyzer_utilities/lib/messages.dart

@@ -448,12 +448,19 @@ class DiagnosticTables {
                     analyzerCode.snakeCaseName] ??=
                 [])
             .add(message);
-        var diagnosticClass = analyzerCode.diagnosticClass;
-        if (!message.isRemoved && message is! AliasMessage) {
-          (activeMessagesByPackage[diagnosticClass.file.package] ??= []).add(
-            message,
+        var package = message.package;
+        if (analyzerCode.diagnosticClass.file.package != package) {
+          throw LocatedError(
+            'Expected to generate this analyzer code to '
+            'package:${package.dirName}, but its diagnostic class '
+            '(${analyzerCode.diagnosticClass.name}) lives in '
+            'package:${analyzerCode.diagnosticClass.file.package.dirName}',
+            span: message.keySpan,
           );
         }
+        if (!message.isRemoved && message is! AliasMessage) {
+          (activeMessagesByPackage[package] ??= []).add(message);
+        }
       }
     }
 
@@ -980,6 +987,9 @@ class SharedMessage extends CfeStyleMessage with MessageWithAnalyzerCode {
       ),
       hasPublishedDocs = messageYaml.getBool('hasPublishedDocs');
 
+  @override
+  AnalyzerDiagnosticPackage get package => AnalyzerDiagnosticPackage.analyzer;
+
   static AnalyzerCode _decodeAnalyzerCode(YamlNode node) {
     switch (node) {
       case YamlScalar(value: String s):