fix: Design of validateValues

packages/config/lib/src/config/config.dart

@@ -8,6 +8,7 @@ export 'exceptions.dart';
 export 'file_system_options.dart';
 export 'multi_config_source.dart';
 export 'option_groups.dart';
+export 'option_resolution_data.dart';
 export 'option_types.dart';
 export 'options.dart';
 export 'output_formatting.dart' show formatConfigError;

packages/config/lib/src/config/option_groups.dart

@@ -1,5 +1,5 @@
 import 'exceptions.dart';
-import 'option_resolution.dart';
+import 'option_resolution_data.dart';
 import 'options.dart';
 
 enum MutuallyExclusiveMode {
@@ -49,7 +49,7 @@ class MutuallyExclusive extends OptionGroup {
 
   @override
   String? validateValues(
-    final Map<OptionDefinition, OptionResolution> optionResolutions,
+    final Map<OptionDefinition, OptionResolutionData> optionResolutions,
   ) {
     final allowDefaults = mode == MutuallyExclusiveMode.allowDefaults;
     final providedCount = optionResolutions.values

packages/config/lib/src/config/option_resolution.dart

@@ -1,11 +1,7 @@
+import 'option_resolution_data.dart';
 import 'source_type.dart';
 
-final class OptionResolution<V> {
-  final String? stringValue;
-  final V? value;
-  final String? error;
-  final ValueSourceType source;
-
+final class OptionResolution<V> with OptionResolutionData<V> {
   const OptionResolution._({
     required this.source,
     this.stringValue,
@@ -44,12 +40,15 @@ final class OptionResolution<V> {
         error: error,
       );
 
-  /// Whether the option has a proper value (without errors).
-  bool get hasValue => source != ValueSourceType.noValue && error == null;
+  @override
+  final String? stringValue;
 
-  /// Whether the option has a value that was specified explicitly (not default).
-  bool get isSpecified => hasValue && source != ValueSourceType.defaultValue;
+  @override
+  final V? value;
 
-  /// Whether the option has the default value.
-  bool get isDefault => hasValue && source == ValueSourceType.defaultValue;
+  @override
+  final String? error;
+
+  @override
+  final ValueSourceType source;
 }

packages/config/lib/src/config/option_resolution_data.dart

@@ -0,0 +1,28 @@
+import 'source_type.dart';
+
+/// Provides significant metadata about an option once it is resolved.
+base mixin OptionResolutionData<V> {
+  /// The resolved value of the option.
+  V? get value;
+
+  /// The source from where the option has been resolved.
+  ValueSourceType get source;
+
+  /// The string value of the option.
+  String? get stringValue;
+
+  /// Error message, if any, apropos of option resolution.
+  String? get error;
+
+  /// Whether there was an error during resolving the option.
+  bool get hasError => error != null;
+
+  /// Whether the option has a proper value (without errors).
+  bool get hasValue => !hasError && source != ValueSourceType.noValue;
+
+  /// Whether the option has a value that was specified explicitly (not default).
+  bool get isSpecified => hasValue && source != ValueSourceType.defaultValue;
+
+  /// Whether the option has the default value.
+  bool get isDefault => hasValue && source == ValueSourceType.defaultValue;
+}

packages/config/lib/src/config/options.dart

@@ -7,6 +7,7 @@ import 'configuration.dart';
 import 'configuration_broker.dart';
 import 'exceptions.dart';
 import 'option_resolution.dart';
+import 'option_resolution_data.dart';
 import 'source_type.dart';
 
 /// Common interface to enable same treatment for [ConfigOptionBase]
@@ -64,7 +65,7 @@ class OptionGroup {
   ///
   /// Subclasses may override this method to perform specific validations.
   String? validateValues(
-    final Map<OptionDefinition, OptionResolution> optionResolutions,
+    final Map<OptionDefinition, OptionResolutionData> optionResolutions,
   ) {
     return null;
   }