Fix cache corruption in incremental resolver

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

Index: pkg/analyzer/lib/src/dart/element/element.dart
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 9677e893fea33b68fae76034c98569be2a5fee91..4b031464d10b1cabaeda8af3d800bd811258c55a 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -1789,11 +1789,12 @@ abstract class ElementImpl implements Element {
 
   /**
    * Set the enclosing element of this element to the given [element].
+   *
+   * Throws [FrozenHashCodeException] if the hashCode can't be changed.
    */
   void set enclosingElement(Element element) {
     _enclosingElement = element as ElementImpl;
-    _cachedLocation = null;
-    _cachedHashCode = null;
+    _updateCaches();
   }
 
   @override
@@ -1865,10 +1866,15 @@ abstract class ElementImpl implements Element {
   @override
   String get name => _name;
 
+
+  /**
+   * Changes the name of this element.
+   *
+   * Throws [FrozenHashCodeException] if the hashCode can't be changed.
+   */
   void set name(String name) {
     this._name = name;
-    _cachedLocation = null;
-    _cachedHashCode = null;
+    _updateCaches();
   }
 
   @override
@@ -1880,11 +1886,12 @@ abstract class ElementImpl implements Element {
   /**
    * Sets the offset of the name of this element in the file that contains the
    * declaration of this element.
+   *
+   * Throws [FrozenHashCodeException] if the hashCode can't be changed.
    */
   void set nameOffset(int offset) {
     _nameOffset = offset;
-    _cachedHashCode = null;
-    _cachedLocation = null;
+    _updateCaches();
   }
 
   @override
@@ -2045,6 +2052,35 @@ abstract class ElementImpl implements Element {
   void visitChildren(ElementVisitor visitor) {
     // There are no children to visit
   }
+
+  /**
+   *  Updates cached values after an input changed.
+   *
+   *  Throws [FrozenHashCodeException] if not allowed.
+   */
+  void _updateCaches() {
+    if (!hasModifier(Modifier.CACHE_KEY)) {
+      // Fast path.
+      _cachedLocation = null;
+      _cachedHashCode = null;
+      return;
+    }
+
+    // Save originals.
+    ElementLocation oldLocation = _cachedLocation;
+    int oldHashCode = _cachedHashCode;
+
+    _cachedLocation = null;
+    _cachedHashCode = null;
+
+    if (oldHashCode != hashCode) {
+      // Prevent cache corruption by restoring originals.
+      _cachedLocation = oldLocation;
+      _cachedHashCode = oldHashCode;
+      throw new FrozenHashCodeException(
+          "can't update hashCode for a cache key: $this ($runtimeType)");
+    }
+  }
 }
 
 /**
@@ -2575,6 +2611,18 @@ class FieldFormalParameterElementImpl extends ParameterElementImpl
 }
 
 /**
+ * Indicates that an ElementImpl's hashCode cannot currently be changed.
+ */
+class FrozenHashCodeException implements Exception {
+  final String _message;
+
+  FrozenHashCodeException(this._message);
+
+  @override
+  String toString() => "FrozenHashCodeException($_message)";
+}
+
+/**
  * A concrete implementation of a [FunctionElement].
  */
 class FunctionElementImpl extends ExecutableElementImpl
@@ -3815,7 +3863,12 @@ class Modifier extends Enum<Modifier> {
    */
   static const Modifier SYNTHETIC = const Modifier('SYNTHETIC', 18);
 
-  static const List<Modifier> values = const [
+  /**
+   * Indicates that this element is being used as an analyzer cache key.
+   */
+  static const Modifier CACHE_KEY = const Modifier('CACHE_KEY', 19);
+
+  static const List<Modifier> persistedValues = const [
     ABSTRACT,
     ASYNCHRONOUS,
     CONST,
@@ -3837,6 +3890,11 @@ class Modifier extends Enum<Modifier> {
     SYNTHETIC
   ];
 
+  static const List<Modifier> transientValues = const [CACHE_KEY];
+
+  static final values = new List.unmodifiable(
+      []..addAll(persistedValues)..addAll(transientValues));
+
   const Modifier(String name, int ordinal) : super(name, ordinal);
 }