[Feature] InheritedAttribute - Extend Mix functionality with custom attributes.

lib/mix.dart

@@ -26,3 +26,5 @@ export 'src/theme/mix_theme.dart';
 export 'src/theme/refs/color_token.dart';
 export 'src/theme/refs/text_style_token.dart';
 export 'src/variants/variants.dart';
+
+

lib/src/attributes/common/attribute.dart

@@ -10,6 +10,27 @@ abstract class Attribute {
   const Attribute();
 }
 
+/// An interface that add support to custom attributes for [MixContext].
+abstract class InheritedAttribute<T extends InheritedAttribute<T>>
+    extends Attribute {
+  const InheritedAttribute();
+
+  InheritedAttribute<T> merge(covariant InheritedAttribute<T>? other);
+
+  Object get type => T;
+}
+
+class InheritedAttributes {
+  final Map<Object, InheritedAttribute<dynamic>> attributes;
+
+  InheritedAttributes(this.attributes);
+
+  /// Used to obtain a [InheritedAttribute] from [MixContext].
+  ///
+  /// Obtain with `mixContext.fromType<MyAttributeExtension>()`.
+  T? fromType<T>() => attributes[T] as T?;
+}
+
 /// Allows to pass down Mixes as attributes for use with helpers
 class NestedAttribute<T extends Attribute> extends Attribute {
   const NestedAttribute(this.attributes);

lib/src/mixer/mix_context.dart

@@ -28,6 +28,7 @@ extension DecoratorMapExtension on DecoratorMap {
 
 class MixContext {
   final BuildContext context;
+  final InheritedAttributes inheritedAttributes;
   final Mix sourceMix;
   final Mix originalMix;
 
@@ -42,6 +43,16 @@ class MixContext {
   final FlexProps flexProps;
   final ZBoxProps zBoxProps;
 
+  /// Used to obtain a [InheritedAttribute] from [InheritedAttributes].
+  ///
+  /// Obtain with `mixContext.fromType<MyInheritedAttribute>()`.
+  T fromType<T extends InheritedAttribute<T>>() {
+    final attribute = inheritedAttributes.fromType<T>();
+    debugCheckInheritedAttribute<T>(attribute);
+
+    return attribute!;
+  }
+
   MixContext._({
     required this.context,
     required this.sourceMix,
@@ -55,6 +66,7 @@ class MixContext {
     required this.directives,
     required this.variants,
     required this.decorators,
+    required this.inheritedAttributes,
   });
 
   factory MixContext.create({
@@ -93,6 +105,7 @@ class MixContext {
     required Mix<T> mix,
   }) {
     final _attributes = _expandAttributes(context, mix);
+
     BoxAttributes? boxAttributes;
     IconAttributes? iconAttributes;
     FlexAttributes? flexAttributes;
@@ -105,7 +118,21 @@ class MixContext {
     final variants = <VariantAttribute>[];
     final decorators = <Decorator>[];
 
+    final Map<Object, InheritedAttribute> inheritedAttributesMap = {};
+
     for (final attribute in _attributes) {
+      if (attribute is InheritedAttribute) {
+        var inheritedAttribute = inheritedAttributesMap[attribute.type];
+
+        if (inheritedAttribute == null) {
+          inheritedAttribute = attribute;
+        } else {
+          inheritedAttribute = inheritedAttribute.merge(attribute);
+        }
+
+        inheritedAttributesMap[attribute.type] = inheritedAttribute;
+      }
+
       if (attribute is VariantAttribute) {
         variants.add(attribute);
       }
@@ -211,6 +238,7 @@ class MixContext {
       directives: directives,
       variants: variants,
       decorators: decoratorMap,
+      inheritedAttributes: InheritedAttributes(inheritedAttributesMap),
     );
   }
 
@@ -335,3 +363,16 @@ class MixContext {
   //   );
   // }
 }
+
+/// Asserts that the given mixContext has a [T] attribute.
+void debugCheckInheritedAttribute<T extends InheritedAttribute<T>>(
+  InheritedAttribute? attribute,
+) {
+  assert(() {
+    return attribute is T;
+  }(), '''
+   No $T could be found starting from the mixContext 
+   when call mixContext.fromType<$T>(). This can happen because you 
+   have not create a Mix with $T.
+  ''');
+}

lib/src/mixer/mix_factory.dart

@@ -119,6 +119,7 @@ class Mix<T extends Attribute> {
   }
 
   /// Merges many mixes into one
+  // ignore: long-parameter-list
   static Mix<T> combine<T extends Attribute>([
     Mix<T>? mix1,
     Mix<T>? mix2,

lib/src/widgets/box.widget.dart

@@ -117,3 +117,4 @@ class BoxMixedWidget extends MixedWidget {
     return current;
   }
 }
+

lib/src/widgets/mix_context_builder.dart

@@ -6,7 +6,9 @@ import 'package:mix/src/variants/variants.dart';
 import 'package:mix/src/widgets/mixable.widget.dart';
 
 typedef WidgetMixBuilder<T> = Widget Function(
-    BuildContext context, MixContext mixContext);
+  BuildContext context,
+  MixContext mixContext,
+);
 
 class MixContextBuilder extends MixableWidget {
   const MixContextBuilder({
@@ -27,6 +29,7 @@ class MixContextBuilder extends MixableWidget {
   @override
   Widget build(BuildContext context) {
     final mixContext = getMixContext(context);
+
     return MixContextNotifier(
       mixContext,
       child: builder(
@@ -36,3 +39,4 @@ class MixContextBuilder extends MixableWidget {
     );
   }
 }
+

lib/src/widgets/mixable.widget.dart

@@ -46,8 +46,11 @@ abstract class MixableWidget extends StatelessWidget {
       DiagnosticsProperty<Mix>('mix', _mix, defaultValue: null),
     );
     properties.add(
-      DiagnosticsProperty<List<Variant>>('variants', _variants,
-          defaultValue: null),
+      DiagnosticsProperty<List<Variant>>(
+        'variants',
+        _variants,
+        defaultValue: null,
+      ),
     );
     properties.add(
       DiagnosticsProperty<bool>('inherit', _inherit, defaultValue: true),