Throw if the main argument in plurals does not match the argument list.

pkgs/intl_translation/CHANGELOG.md

@@ -1,5 +1,6 @@
-## 0.20.1-wip
+## 0.20.1
   * Add topics to `pubspec.yaml`
+  * Throw if the main argument in plurals and selects does not match the argument list.
 
 ## 0.20.0
   * Throw if the `Intl.select` `arg` is not in the list of `args`.

pkgs/intl_translation/lib/src/messages/submessages/submessage.dart

@@ -94,7 +94,14 @@ abstract class SubMessage extends ComplexMessage {
   List toJson() {
     var json = [];
     json.add(dartMessageName);
-    json.add(arguments.indexOf(mainArgument));
+    var indexOf = arguments.indexOf(mainArgument);
+    if (indexOf == -1) {
+      // This is an error as this should have been checked in
+      // lib/visitors/plural_gender_visitor.dart already.
+      throw ArgumentError('The argument `$mainArgument` could not be found in '
+          '`$arguments`.');
+    }
+    json.add(indexOf);
     for (var arg in codeAttributeNames) {
       json.add(this[arg]?.toJson());
     }

pkgs/intl_translation/lib/visitors/plural_gender_visitor.dart

@@ -137,6 +137,13 @@ class PluralAndGenderVisitor extends SimpleAstVisitor<void> {
       extraction.warnings.add(errString);
     }
 
+    if (!message.arguments.contains(message.mainArgument)) {
+      throw Exception(
+          'Argument `${message.mainArgument}` could not be found in '
+          '${message.arguments} while processing $node. The parent argument '
+          'name must match the one in the `Intl.` call.');
+    }
+
     return message;
   }
 }

pkgs/intl_translation/pubspec.yaml

@@ -1,5 +1,5 @@
 name: intl_translation
-version: 0.20.1-wip
+version: 0.20.1
 description: >-
   Contains code to deal with internationalized/localized messages,
   date and number formatting and parsing, bi-directional text, and