Rework handling of potentially-constant variables.

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 8a5d55a2a14fdc5094e2c10e53d6995d35f2c201..2c3e830ab95f03df9bbbc4cce2f35acc0d26fc1f 100644
--- a/pkg/analyzer/lib/src/generated/element.dart
+++ b/pkg/analyzer/lib/src/generated/element.dart
@@ -2137,7 +2137,7 @@ class ConstTopLevelVariableElementImpl extends TopLevelVariableElementImpl
  *
  * This class is not intended to be part of the public API for analyzer.
  */
-abstract class ConstVariableElement implements PotentiallyConstVariableElement {
+abstract class ConstVariableElement {
   /**
    * If this element represents a constant variable, and it has an initializer,
    * a copy of the initializer for the constant.  Otherwise `null`.
@@ -4183,7 +4183,6 @@ abstract class FieldElement
  * A concrete implementation of a [FieldElement].
  */
 class FieldElementImpl extends PropertyInducingElementImpl
-    with PotentiallyConstVariableElement
     implements FieldElement {
   /**
    * An empty list of field elements.
@@ -7939,7 +7938,6 @@ abstract class LocalVariableElement implements LocalElement, VariableElement {
  * A concrete implementation of a [LocalVariableElement].
  */
 class LocalVariableElementImpl extends VariableElementImpl
-    with PotentiallyConstVariableElement
     implements LocalVariableElement {
   /**
    * An empty list of field elements.
@@ -8876,7 +8874,7 @@ abstract class ParameterElement
  * A concrete implementation of a [ParameterElement].
  */
 class ParameterElementImpl extends VariableElementImpl
-    with ParameterElementMixin, PotentiallyConstVariableElement
+    with ParameterElementMixin
     implements ParameterElement {
   /**
    * An empty list of parameter elements.
@@ -9235,28 +9233,6 @@ class ParameterMember extends VariableMember
 }
 
 /**
- * Interface used by elements that might represent constant variables.
- *
- * This class may be used as a mixin in the case where [constInitializer] is
- * known to return null.
- *
- * This class is not intended to be part of the public API for analyzer.
- */
-abstract class PotentiallyConstVariableElement
-    implements VariableElementImpl, ConstantEvaluationTarget {
-  /**
-   * 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 => null;
-}
-
-/**
  * A prefix used to import one or more libraries into another library.
  */
 abstract class PrefixElement implements Element {
@@ -10065,7 +10041,6 @@ abstract class TopLevelVariableElement implements PropertyInducingElement {
  * A concrete implementation of a [TopLevelVariableElement].
  */
 class TopLevelVariableElementImpl extends PropertyInducingElementImpl
-    with PotentiallyConstVariableElement
     implements TopLevelVariableElement {
   /**
    * An empty list of top-level variable elements.
@@ -10770,6 +10745,17 @@ abstract class VariableElementImpl extends ElementImpl
     setModifier(Modifier.CONST, isConst);
   }
 
+  /**
+   * 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 => null;
+
   @override
   DartObject get constantValue => null;