correct some mixin edge cases

Author: jcollins-g

lib/src/model/accessor.dart

@@ -228,11 +228,11 @@ class ContainerAccessor extends Accessor with ContainerMember, Inheritable {
               isGetter ? t.getGetter(element.name) : t.getSetter(element.name);
           if (accessor != null) {
             accessor = accessor.declaration;
-            Class parentClass =
+            InheritingContainer parentContainer =
                 ModelElement.fromElement(t.element, packageGraph);
             var possibleFields = <Field>[];
-            possibleFields.addAll(parentClass.instanceFields);
-            possibleFields.addAll(parentClass.staticFields);
+            possibleFields.addAll(parentContainer.instanceFields);
+            possibleFields.addAll(parentContainer.staticFields);
             var fieldName = accessor.name.replaceFirst('=', '');
             var foundField = possibleFields.firstWhere(
                 (f) => f.element.name == fieldName,

lib/src/model/inheritable.dart

@@ -117,6 +117,9 @@ mixin Inheritable on ContainerMember {
     var object = packageGraph.specialClasses[SpecialClass.object];
     if (!inheritance.contains(definingEnclosingContainer) &&
         definingEnclosingContainer != null) {
+      if (definingEnclosingContainer != object) {
+        print('wtf');
+      }
       assert(definingEnclosingContainer == object);
     }
     // Unless the code explicitly extends dart-core's Object, we won't get

lib/src/model/mixin.dart

@@ -57,6 +57,16 @@ class Mixin extends InheritingContainer with TypeImplementing {
       _inheritanceChain.addAll(superclassConstraints.expand(
           (ParameterizedElementType i) =>
               (i.modelElement as InheritingContainer).inheritanceChain));
+
+      for (var c
+          in superChain.map((e) => (e.modelElement as InheritingContainer))) {
+        _inheritanceChain.addAll(c.inheritanceChain);
+      }
+
+      /// Interfaces need to come last, because classes in the superChain might
+      /// implement them even when they aren't mentioned.
+      _inheritanceChain.addAll(interfaces.expand(
+          (e) => (e.modelElement as InheritingContainer).inheritanceChain));
     }
     return _inheritanceChain.toList(growable: false);
   }