Changes as per review

pkgs/messages/lib/src/deserializer/deserializer.dart

@@ -6,5 +6,5 @@ import '../message_format.dart';
 import '../plural_selector.dart';
 
 abstract class Deserializer<T extends MessageList> {
-  T deserialize(PluralSelector intl);
+  T deserialize(PluralSelector selector);
 }

pkgs/messages/lib/src/deserializer/deserializer_json.dart

@@ -20,7 +20,7 @@ class JsonDeserializer extends Deserializer<MessageListJson> {
   }
 
   @override
-  MessageListJson deserialize(PluralSelector intl) {
+  MessageListJson deserialize(PluralSelector selector) {
     if (preamble.version != serializationVersion) {
       throw ArgumentError(
           '''This message has version ${preamble.version}, while the deserializer has version $serializationVersion''');
@@ -32,7 +32,7 @@ class JsonDeserializer extends Deserializer<MessageListJson> {
     return MessageListJson(
       preamble,
       _messages,
-      intl,
+      selector,
       mapping?.map((key, value) => MapEntry(
             int.parse(key, radix: serializationRadix),
             int.parse(value as String, radix: serializationRadix),
@@ -89,15 +89,16 @@ class JsonDeserializer extends Deserializer<MessageListJson> {
     for (var i = 0; i < submessages.length - 1; i += 2) {
       final msg = getMessage(submessages[i + 1]);
       final messageMarker = submessages[i];
-      if (messageMarker case Plural.few) {
+      if (messageMarker case PluralMarker.few) {
         fewMessage = msg;
-      } else if (messageMarker case Plural.many) {
+      } else if (messageMarker case PluralMarker.many) {
         manyMessage = msg;
-      } else if (messageMarker case final int d) {
-        numberCases[d] = msg;
+      } else if (messageMarker case final int digit) {
+        numberCases[digit] = msg;
       } else if (messageMarker is String &&
-          messageMarker.startsWith(Plural.wordCase)) {
-        wordCases[int.parse(messageMarker.substring(1))] = msg;
+          messageMarker.startsWith(PluralMarker.wordCase)) {
+        final digit = int.parse(messageMarker.substring(1));
+        wordCases[digit] = msg;
       }
     }
     return PluralMessage(

pkgs/messages/lib/src/message_format.dart

@@ -30,31 +30,15 @@ abstract class Preamble {
 
 abstract class MessageList {
   Preamble get preamble;
-  PluralSelector get intl;
+  PluralSelector get pluralSelector;
 
   String generateStringAtIndex(int index, List args);
 
   String generateStringAtId(String id, List args);
 }
 
-enum PluralEnum {
-  zeroWord,
-  zeroNumber,
-  oneWord,
-  oneNumber,
-  twoWord,
-  twoNumber,
-  few,
-  many,
-}
-
-class Plural {
+sealed class PluralMarker {
   static const String wordCase = 'w';
   static const String few = 'f';
   static const String many = 'm';
 }
-
-class Gender {
-  static const int female = 1;
-  static const int male = 2;
-}

pkgs/messages/lib/src/message_list_json.dart

@@ -40,20 +40,20 @@ class JsonPreamble extends Preamble {
 
 class MessageListJson extends MessageList {
   final List<Message> messages;
-  final PluralSelector _intl;
+  final PluralSelector _selector;
   final JsonPreamble _preamble;
   final Map<int, int>? messageIndices;
 
   @override
-  PluralSelector get intl => _intl;
+  PluralSelector get pluralSelector => _selector;
 
   @override
   Preamble get preamble => _preamble;
 
   MessageListJson(
     this._preamble,
     this.messages,
-    this._intl,
+    this._selector,
     this.messageIndices,
   );
 
@@ -64,11 +64,11 @@ class MessageListJson extends MessageList {
   String generateStringAtId(String id, List args) => messages
       .where((element) => element.id == id)
       .first
-      .generateString(args, pluralSelector: _intl);
+      .generateString(args, pluralSelector: _selector);
 
   @override
   String generateStringAtIndex(int index, List args) =>
-      messages[getIndex(index)].generateString(args, pluralSelector: _intl);
+      messages[getIndex(index)].generateString(args, pluralSelector: _selector);
 
   int getIndex(int index) => messageIndices?[index] ?? index;
 }

pkgs/messages_builder/lib/generation_options.dart

@@ -36,9 +36,10 @@ class GenerationOptions {
   /// dart native code.
   final DeserializationType deserialization;
 
-  ///
+  /// The header to add to all generated files, for example for licensing.
   final String header;
 
+  /// The origin of the algorithm for determining which plural case to use.
   final PluralSelectorType pluralSelector;
 
   GenerationOptions({
@@ -62,21 +63,31 @@ class GenerationOptions {
       deserialization: DeserializationType.web,
       messageCalls: (messagesOptions?['generateMethods'] as bool?) ?? true,
       findById: (messagesOptions?['generateFindById'] as bool?) ?? false,
-      indexType: IndexType.values
-              .where((type) =>
-                  type.name == messagesOptions?['generateFindBy'] as String?)
-              .firstOrNull ??
-          IndexType.integer,
+      indexType: _indexType(messagesOptions),
       header: messagesOptions?['header'] as String? ??
           'Generated by package:messages_builder.',
-      pluralSelector: PluralSelectorType.values
-              .where((type) =>
-                  type.name == messagesOptions?['pluralSelector'] as String?)
-              .firstOrNull ??
-          PluralSelectorType.intl,
+      pluralSelector: _pluralSelector(messagesOptions),
     );
     return generationOptions;
   }
+
+  static IndexType _indexType(YamlMap? messagesOptions) {
+    final generateFindString = messagesOptions?['generateFindBy'] as String?;
+    return generateFindString != null
+        ? IndexType.values
+            .where((type) => type.name == generateFindString)
+            .first
+        : IndexType.integer;
+  }
+
+  static PluralSelectorType _pluralSelector(YamlMap? messagesOptions) {
+    final pluralSelectorString = messagesOptions?['pluralSelector'] as String?;
+    return pluralSelectorString != null
+        ? PluralSelectorType.values
+            .where((type) => type.name == pluralSelectorString)
+            .first
+        : PluralSelectorType.intl;
+  }
 }
 
 enum SerializationType {
@@ -87,14 +98,27 @@ enum DeserializationType {
   web;
 }
 
+/// How the indexing of the messages should be implemented.
 enum IndexType {
+  /// No indexing.
   none,
+
+  /// Indexing via a collection of `static int`s.
   integer,
+
+  /// Indexing via an enum.
   enumerate;
 }
 
+/// The origin of the algorithm for determining which plural case to use.
 enum PluralSelectorType {
+  /// From `package:intl`.
   intl,
+
+  /// From `package:intl4x`.
+
   intl4x,
+
+  /// A user-specified algorithm.
   custom;
 }

pkgs/messages_serializer/lib/src/serializer_json.dart

@@ -134,19 +134,20 @@ class JsonSerializer extends Serializer<String> {
     m.add(encodeMessage(message.other));
     final caseIndices = <Object>[];
     if (message.few != null) {
-      caseIndices.add(Plural.few);
+      caseIndices.add(PluralMarker.few);
       caseIndices.add(encodeMessage(message.few!));
     }
     if (message.many != null) {
-      caseIndices.add(Plural.many);
+      caseIndices.add(PluralMarker.many);
       caseIndices.add(encodeMessage(message.many!));
     }
-    for (final entry in message.numberCases.entries) {
-      caseIndices.add(entry.key);
-      caseIndices.add(encodeMessage(entry.value));
+    for (final MapEntry(key: caseIndex, value: messageIndex)
+        in message.numberCases.entries) {
+      caseIndices.add(caseIndex);
+      caseIndices.add(encodeMessage(messageIndex));
     }
     for (final entry in message.wordCases.entries) {
-      caseIndices.add(Plural.wordCase + entry.key.toString());
+      caseIndices.add(PluralMarker.wordCase + entry.key.toString());
       caseIndices.add(encodeMessage(entry.value));
     }
     m.add(caseIndices);

pkgs/messages_shrinker/lib/messages_shrinker.dart

@@ -34,7 +34,8 @@ class MessageShrinker {
     final sizeBefore = buffer.length;
     final json = JsonDeserializer(buffer).deserialize(
       (howMany, {few, locale, many, numberCases, required other, wordCases}) {
-        throw UnimplementedError();
+        throw StateError('As the deserialized MessageList is not used, but '
+            'just immediately reserialized, this selector will not be called.');
       },
     );
     final data = JsonSerializer(json.preamble.hasIds)