Improve error reporting when a mixin application is invalid.

pkg/analyzer/lib/src/generated/element.dart

Index: pkg/analyzer/lib/src/generated/element.dart
diff --git a/pkg/analyzer/lib/src/generated/element.dart b/pkg/analyzer/lib/src/generated/element.dart
index 617faf3ff742ecb6b6f7ac72fe4ac41782afa1cd..dce1f1d490e34d56c4d979a9738bcc127dfcdb34 100644
--- a/pkg/analyzer/lib/src/generated/element.dart
+++ b/pkg/analyzer/lib/src/generated/element.dart
@@ -1056,6 +1056,12 @@ abstract class ClassElement implements Element {
   bool get isValidMixin;
 
   /**
+   * Return `true` if this mixin errors have already been reported for this
+   * class.
+   */
+  bool get mixinErrorsReported;

[scheglov, 2014/11/13 23:02:46]

Do we really need to add it to the API?
Can we add it only to the implementation, or even better - to one of the
resolution classes?

+
+  /**
    * Return the element representing the method that results from looking up the given method in
    * this class with respect to the given library, ignoring abstract methods, or `null` if the
    * look up fails. The behavior of this method is defined by the Dart Language Specification in
@@ -1530,6 +1536,9 @@ class ClassElementImpl extends ElementImpl implements ClassElement {
   bool get isValidMixin => hasModifier(Modifier.MIXIN);
 
   @override
+  bool get mixinErrorsReported => hasModifier(Modifier.MIXIN_ERRORS_REPORTED);
+
+  @override
   MethodElement lookUpConcreteMethod(String methodName, LibraryElement library) => _internalLookUpConcreteMethod(methodName, library, true);
 
   @override
@@ -1629,6 +1638,14 @@ class ClassElementImpl extends ElementImpl implements ClassElement {
   }
 
   /**
+   * Set whether an error has reported explaining why this class is an
+   * invalid mixin application.
+   */
+  void set mixinErrorsReported(bool value) {
+    setModifier(Modifier.MIXIN_ERRORS_REPORTED, value);
+  }
+
+  /**
    * Set whether this class is defined by a typedef construct to correspond to the given value.
    *
    * @param isTypedef `true` if the class is defined by a typedef construct
@@ -8737,42 +8754,49 @@ class Modifier extends Enum<Modifier> {
   static const Modifier MIXIN = const Modifier('MIXIN', 10);
 
   /**
+   * Indicates that an error has reported explaining why this class is an
+   * invalid mixin application.
+   */
+  static const Modifier MIXIN_ERRORS_REPORTED =
+      const Modifier('MIXIN_ERRORS_REPORTED', 11);
+
+  /**
    * Indicates that the value of a parameter or local variable might be mutated within the context.
    */
-  static const Modifier POTENTIALLY_MUTATED_IN_CONTEXT = const Modifier('POTENTIALLY_MUTATED_IN_CONTEXT', 11);
+  static const Modifier POTENTIALLY_MUTATED_IN_CONTEXT = const Modifier('POTENTIALLY_MUTATED_IN_CONTEXT', 12);
 
   /**
    * Indicates that the value of a parameter or local variable might be mutated within the scope.
    */
-  static const Modifier POTENTIALLY_MUTATED_IN_SCOPE = const Modifier('POTENTIALLY_MUTATED_IN_SCOPE', 12);
+  static const Modifier POTENTIALLY_MUTATED_IN_SCOPE = const Modifier('POTENTIALLY_MUTATED_IN_SCOPE', 13);
 
   /**
    * Indicates that a class contains an explicit reference to 'super'.
    */
-  static const Modifier REFERENCES_SUPER = const Modifier('REFERENCES_SUPER', 13);
+  static const Modifier REFERENCES_SUPER = const Modifier('REFERENCES_SUPER', 14);
 
   /**
    * Indicates that the pseudo-modifier 'set' was applied to the element.
    */
-  static const Modifier SETTER = const Modifier('SETTER', 14);
+  static const Modifier SETTER = const Modifier('SETTER', 15);
 
   /**
    * Indicates that the modifier 'static' was applied to the element.
    */
-  static const Modifier STATIC = const Modifier('STATIC', 15);
+  static const Modifier STATIC = const Modifier('STATIC', 16);
 
   /**
    * Indicates that the element does not appear in the source code but was implicitly created. For
    * example, if a class does not define any constructors, an implicit zero-argument constructor
    * will be created and it will be marked as being synthetic.
    */
-  static const Modifier SYNTHETIC = const Modifier('SYNTHETIC', 16);
+  static const Modifier SYNTHETIC = const Modifier('SYNTHETIC', 17);
 
   /**
    * Indicates that a class was defined using an alias. TODO(brianwilkerson) This should be renamed
    * to 'ALIAS'.
    */
-  static const Modifier TYPEDEF = const Modifier('TYPEDEF', 17);
+  static const Modifier TYPEDEF = const Modifier('TYPEDEF', 18);
 
   static const List<Modifier> values = const [
       ABSTRACT,
@@ -8786,6 +8810,7 @@ class Modifier extends Enum<Modifier> {
       GETTER,
       HAS_EXT_URI,
       MIXIN,
+      MIXIN_ERRORS_REPORTED,
       POTENTIALLY_MUTATED_IN_CONTEXT,
       POTENTIALLY_MUTATED_IN_SCOPE,
       REFERENCES_SUPER,