First step to resolving simple API changes.

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 6fef2d8e20c2a1d263419f4b3e251bfe6b54bdea..2dd8ad40da217aee4ef3091c0d6d6fa7a7135900 100644
--- a/pkg/analyzer/lib/src/generated/element.dart
+++ b/pkg/analyzer/lib/src/generated/element.dart
@@ -3104,6 +3104,11 @@ abstract class Element {
   Element get enclosingElement;
 
   /**
+   * The unique integer identifier of this element.
+   */
+  int get id;
+
+  /**
    * Return `true` if this element has an annotation of the form '@deprecated' or
    * '@Deprecated('..')'.
    *
@@ -3224,6 +3229,11 @@ abstract class Element {
   CompilationUnit get unit;
 
   /**
+   * Identifies of the elements that use this elements.
+   */
+  IntSet get users;

[Brian Wilkerson, 2014/12/05 23:05:57]

I'm concerned about keeping around unnecessary empty sets. It would be good to
measure to see what percentage of elements have empty sets and consider storing
'null' in place of empty sets if there would be a reasonable space savings from
doing so. (But not before this CL lands.)

[scheglov, 2014/12/05 23:49:05]

Acknowledged.

+
+  /**
    * Use the given visitor to visit this element.
    *
    * @param visitor the visitor that will visit this element
@@ -3232,6 +3242,11 @@ abstract class Element {
   accept(ElementVisitor visitor);
 
   /**
+   * Remember the given [element] as a user of this element.
+   */
+  void addUser(Element element);
+
+  /**
    * Return the documentation comment for this element as it appears in the original source
    * (complete with the beginning and ending delimiters), or `null` if this element does not
    * have a documentation comment associated with it. This can be a long-running operation if the
@@ -3429,6 +3444,10 @@ class ElementAnnotationImpl implements ElementAnnotation {
  * an [Element].
  */
 abstract class ElementImpl implements Element {
+  static int _NEXT_ID = 0;
+
+  final int id = _NEXT_ID++;
+
   /**
    * The enclosing element of this element, or `null` if this element is at the root of the
    * element structure.
@@ -3467,6 +3486,11 @@ abstract class ElementImpl implements Element {
   ElementLocation _cachedLocation;
 
   /**
+   * Identifies of the elements that use this elements.
+   */
+  final IntSet users = new IntSet();
+
+  /**
    * Initialize a newly created element to have the given name.
    *
    * @param name the name of this element
@@ -3506,6 +3530,8 @@ abstract class ElementImpl implements Element {
    */
   void set enclosingElement(Element element) {
     _enclosingElement = element as ElementImpl;
+    _cachedLocation = null;
+    _cachedHashCode = null;
   }
 
   @override
@@ -3623,6 +3649,11 @@ abstract class ElementImpl implements Element {
         (object as Element).location == location;
   }
 
+  @override
+  void addUser(Element element) {
+    users.add(element.id);
+  }
+
   /**
    * Append a textual representation of this element to the given [buffer].
    */
@@ -8952,6 +8983,8 @@ abstract class Member implements Element {
   @override
   String get displayName => _baseElement.displayName;
 
+  int get id => _baseElement.id;
+
   @override
   bool get isDeprecated => _baseElement.isDeprecated;
 
@@ -8994,6 +9027,13 @@ abstract class Member implements Element {
   @override
   CompilationUnit get unit => _baseElement.unit;
 
+  IntSet get users => _baseElement.users;
+
+  @override
+  void addUser(Element element) {
+    _baseElement.addUser(element);
+  }
+
   @override
   String computeDocumentationComment() =>
       _baseElement.computeDocumentationComment();
@@ -9452,6 +9492,11 @@ abstract class MultiplyDefinedElement implements Element {
  */
 class MultiplyDefinedElementImpl implements MultiplyDefinedElement {
   /**
+   * The unique integer identifier of this element.
+   */
+  final int id = ElementImpl._NEXT_ID++;
+
+  /**
    * The analysis context in which the multiply defined elements are defined.
    */
   final AnalysisContext context;
@@ -9534,8 +9579,14 @@ class MultiplyDefinedElementImpl implements MultiplyDefinedElement {
   CompilationUnit get unit => null;
 
   @override
+  IntSet get users => new IntSet();
+
+  @override
   accept(ElementVisitor visitor) => visitor.visitMultiplyDefinedElement(this);
 
+  void addUser(Element element) {
+  }
+
   @override
   String computeDocumentationComment() => null;