Begin making copies of AST nodes for constants during resolution.

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 082415cd58cedbf4d92a52ce267d67378d23f01b..24f5c13e72725730d8f558b5ba3fcb474fc69cf6 100644
--- a/pkg/analyzer/lib/src/generated/element.dart
+++ b/pkg/analyzer/lib/src/generated/element.dart
@@ -1493,13 +1493,19 @@ class CompilationUnitElementImpl extends UriReferencedElementImpl
 /**
  * A [FieldElement] for a 'const' field that has an initializer.
  */
-class ConstFieldElementImpl extends FieldElementImpl {
+class ConstFieldElementImpl extends FieldElementImpl
+    implements ConstVariableElementImpl {
   /**
    * The result of evaluating this variable's initializer.
    */
   EvaluationResultImpl _result;
 
   /**
+   * A copy of the AST for the variable's initializer.
+   */
+  Expression _constantInitializer;
+
+  /**
    * Initialize a newly created field element to have the given [name].
    */
   ConstFieldElementImpl.con1(Identifier name) : super.forNode(name);
@@ -1511,6 +1517,14 @@ class ConstFieldElementImpl extends FieldElementImpl {
   ConstFieldElementImpl.con2(String name, int offset) : super(name, offset);
 
   @override
+  Expression get constantInitializer => _constantInitializer;

[scheglov, 2015/04/01 23:34:16]

It looks that we don't process this field.
So, why not just convert _constantInitializer into a public field
"constantInitializer"?

[Paul Berry, 2015/04/02 15:18:49]

Done.

+
+  @override
+  void set constantInitializer(Expression value) {
+    _constantInitializer = value;
+  }
+
+  @override
   EvaluationResultImpl get evaluationResult => _result;
 
   @override
@@ -1523,16 +1537,36 @@ class ConstFieldElementImpl extends FieldElementImpl {
  * A [LocalVariableElement] for a local 'const' variable that has an
  * initializer.
  */
-class ConstLocalVariableElementImpl extends LocalVariableElementImpl {
+class ConstLocalVariableElementImpl extends LocalVariableElementImpl
+    implements ConstVariableElementImpl {
   /**
    * The result of evaluating this variable's initializer.
    */
   EvaluationResultImpl _result;
 
   /**
+   * A copy of the AST for the variable's initializer.
+   */
+  Expression _constantInitializer;
+
+  /**
+   * Initialize a newly created local variable element to have the given [name]
+   * and [offset].
+   */
+  ConstLocalVariableElementImpl(String name, int offset) : super(name, offset);
+
+  /**
    * Initialize a newly created local variable element to have the given [name].
    */
-  ConstLocalVariableElementImpl(Identifier name) : super.forNode(name);
+  ConstLocalVariableElementImpl.forNode(Identifier name) : super.forNode(name);
+
+  @override
+  Expression get constantInitializer => _constantInitializer;
+
+  @override
+  void set constantInitializer(Expression value) {
+    _constantInitializer = value;
+  }
 
   @override
   EvaluationResultImpl get evaluationResult => _result;
@@ -1629,6 +1663,12 @@ class ConstructorElementImpl extends ExecutableElementImpl
   int nameEnd;
 
   /**
+   * True if this constructor has been found by constant evaluation to be free
+   * of redirect cycles, and is thus safe to evaluate.
+   */
+  bool isCycleFree = false;
+
+  /**
    * Initialize a newly created constructor element to have the given [name] and
    * [offset].
    */
@@ -1826,19 +1866,33 @@ class ConstructorMember extends ExecutableMember implements ConstructorElement {
  * A [TopLevelVariableElement] for a top-level 'const' variable that has an
  * initializer.
  */
-class ConstTopLevelVariableElementImpl extends TopLevelVariableElementImpl {
+class ConstTopLevelVariableElementImpl extends TopLevelVariableElementImpl
+    implements ConstVariableElementImpl {
   /**
    * The result of evaluating this variable's initializer.
    */
   EvaluationResultImpl _result;
 
   /**
+   * A copy of the AST for the variable's initializer.
+   */
+  Expression _constantInitializer;
+
+  /**
    * Initialize a newly created top-level variable element to have the given
    * [name].
    */
   ConstTopLevelVariableElementImpl(Identifier name) : super.forNode(name);
 
   @override
+  Expression get constantInitializer => _constantInitializer;
+
+  @override
+  void set constantInitializer(Expression value) {
+    _constantInitializer = value;
+  }
+
+  @override
   EvaluationResultImpl get evaluationResult => _result;
 
   @override
@@ -1848,6 +1902,27 @@ class ConstTopLevelVariableElementImpl extends TopLevelVariableElementImpl {
 }
 
 /**
+ * Common interface shared by elements that represent constant variables and
+ * have initializers.
+ *
+ * Note that in correct Dart code, all constant variables must have
+ * initializers.  However, analyzer also needs to handle incorrect Dart code,
+ * in which case there might be some constant variables that lack initializers.
+ * This interface is only used for constant variables that have initializers.
+ *
+ * This class has "Impl" in the name to emphasize the fact that it is not
+ * intended to be part of the public API for analyzer.

[Brian Wilkerson, 2015/04/01 20:31:54]

That's a little odd. When I first saw it I assumed it was a concrete class and
commented that it seemed weird to 'implement' a concrete class that way.

Also, everywhere that implements this interface has the same implementation.
This might be a good place for a mixin.

[Paul Berry, 2015/04/02 15:18:49]

Fair enough.  I've removed "Impl" from the name of this class and
PotentiallyConstVariableElement.
Good idea!  PTAL and let me know if the change looks good to you.  Unfortunately
due to the limitations on mixins I had to remove the "implements" clauses, which
led to some warnings when trying to convert a VariableElement to a
ConstVariableElement or a PotentiallyConstVariableElement.  Fortunately these
warnings were easy to get rid of using "as".

+ */
+abstract class ConstVariableElementImpl
+    extends PotentiallyConstVariableElementImpl {
+  /**
+   * Store a copy of the initializer for this variable (which will later be
+   * usd for evaluating constants).

[Brian Wilkerson, 2015/04/01 20:31:54]

"usd" --> "used"

[Paul Berry, 2015/04/02 15:18:49]

Done.

+   */
+  void set constantInitializer(Expression value);
+}
+
+/**
  * The type associated with elements in the element model.
  */
 abstract class DartType {
@@ -3732,7 +3807,7 @@ abstract class FieldElement
  * A concrete implementation of a [FieldElement].
  */
 class FieldElementImpl extends PropertyInducingElementImpl
-    implements FieldElement {
+    implements FieldElement, PotentiallyConstVariableElementImpl {
   /**
    * An empty list of field elements.
    */
@@ -3750,6 +3825,9 @@ class FieldElementImpl extends PropertyInducingElementImpl
   FieldElementImpl.forNode(Identifier name) : super.forNode(name);
 
   @override
+  Expression get constantInitializer => null;
+
+  @override
   ClassElement get enclosingElement => super.enclosingElement as ClassElement;
 
   @override
@@ -7335,7 +7413,7 @@ abstract class LocalVariableElement implements LocalElement, VariableElement {}
  * A concrete implementation of a [LocalVariableElement].
  */
 class LocalVariableElementImpl extends VariableElementImpl
-    implements LocalVariableElement {
+    implements LocalVariableElement, PotentiallyConstVariableElementImpl {
   /**
    * An empty list of field elements.
    */
@@ -7365,6 +7443,9 @@ class LocalVariableElementImpl extends VariableElementImpl
   LocalVariableElementImpl.forNode(Identifier name) : super.forNode(name);
 
   @override
+  Expression get constantInitializer => null;
+
+  @override
   String get identifier {
     int enclosingOffset =
         enclosingElement != null ? enclosingElement.nameOffset : 0;
@@ -8527,6 +8608,25 @@ class ParameterMember extends VariableMember implements ParameterElement {
 }
 
 /**
+ * Common interface shared by elements that might represent constant variables.
+ *
+ * This class has "Impl" in the name to emphasize the fact that it is not
+ * intended to be part of the public API for analyzer.
+ */
+abstract class PotentiallyConstVariableElementImpl extends VariableElement {
+  /**
+   * If this element represents a constant variable, and it has an initializer,
+   * a copy of the initializer for the constant.  Otherwise `null`.
+   *
+   * Note that in correct Dart code, all constant variables must have
+   * initializers.  However, analyzer also needs to handle incorrect Dart code,
+   * in which case there might be some constant variables that lack
+   * initializers.
+   */
+  Expression get constantInitializer;
+}
+
+/**
  * A prefix used to import one or more libraries into another library.
  */
 abstract class PrefixElement implements Element {
@@ -9307,7 +9407,7 @@ abstract class TopLevelVariableElement implements PropertyInducingElement {}
  * A concrete implementation of a [TopLevelVariableElement].
  */
 class TopLevelVariableElementImpl extends PropertyInducingElementImpl
-    implements TopLevelVariableElement {
+    implements TopLevelVariableElement, PotentiallyConstVariableElementImpl {
   /**
    * An empty list of top-level variable elements.
    */
@@ -9327,6 +9427,9 @@ class TopLevelVariableElementImpl extends PropertyInducingElementImpl
   TopLevelVariableElementImpl.forNode(Identifier name) : super.forNode(name);
 
   @override
+  Expression get constantInitializer => null;
+
+  @override
   bool get isStatic => true;
 
   @override