Add API to force the computation of constant values

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 bcac6b1e3051481fe0cbd7113d66ab579533ba7e..79ff2d3494b083b0736f9c835dd3c258807f49b3 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -27,6 +27,7 @@ import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/utilities_collection.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:analyzer/src/generated/utilities_general.dart';
+import 'package:analyzer/src/task/dart.dart';
 
 /**
  * For AST nodes that could be in both the getter and setter contexts
@@ -1264,11 +1265,6 @@ class CompilationUnitElementImpl extends UriReferencedElementImpl
  */
 class ConstFieldElementImpl extends FieldElementImpl with ConstVariableElement {
   /**
-   * The result of evaluating this variable's initializer.
-   */
-  EvaluationResultImpl _result;
-
-  /**
    * Initialize a newly created synthetic field element to have the given
    * [name] and [offset].
    */
@@ -1278,17 +1274,6 @@ class ConstFieldElementImpl extends FieldElementImpl with ConstVariableElement {
    * Initialize a newly created field element to have the given [name].
    */
   ConstFieldElementImpl.forNode(Identifier name) : super.forNode(name);
-
-  @override
-  DartObject get constantValue => _result?.value;
-
-  @override
-  EvaluationResultImpl get evaluationResult => _result;
-
-  @override
-  void set evaluationResult(EvaluationResultImpl result) {
-    this._result = result;
-  }
 }
 
 /**
@@ -1298,11 +1283,6 @@ class ConstFieldElementImpl extends FieldElementImpl with ConstVariableElement {
 class ConstLocalVariableElementImpl extends LocalVariableElementImpl
     with ConstVariableElement {
   /**
-   * The result of evaluating this variable's initializer.
-   */
-  EvaluationResultImpl _result;
-
-  /**
    * Initialize a newly created local variable element to have the given [name]
    * and [offset].
    */
@@ -1312,17 +1292,6 @@ class ConstLocalVariableElementImpl extends LocalVariableElementImpl
    * Initialize a newly created local variable element to have the given [name].
    */
   ConstLocalVariableElementImpl.forNode(Identifier name) : super.forNode(name);
-
-  @override
-  DartObject get constantValue => _result?.value;
-
-  @override
-  EvaluationResultImpl get evaluationResult => _result;
-
-  @override
-  void set evaluationResult(EvaluationResultImpl result) {
-    this._result = result;
-  }
 }
 
 /**
@@ -1454,11 +1423,6 @@ class ConstructorElementImpl extends ExecutableElementImpl
 class ConstTopLevelVariableElementImpl extends TopLevelVariableElementImpl
     with ConstVariableElement {
   /**
-   * The result of evaluating this variable's initializer.
-   */
-  EvaluationResultImpl _result;
-
-  /**
    * Initialize a newly created synthetic top-level variable element to have the
    * given [name] and [offset].
    */
@@ -1471,17 +1435,6 @@ class ConstTopLevelVariableElementImpl extends TopLevelVariableElementImpl
    */
   ConstTopLevelVariableElementImpl.forNode(Identifier name)
       : super.forNode(name);
-
-  @override
-  DartObject get constantValue => _result?.value;
-
-  @override
-  EvaluationResultImpl get evaluationResult => _result;
-
-  @override
-  void set evaluationResult(EvaluationResultImpl result) {
-    this._result = result;
-  }
 }
 
 /**
@@ -1495,7 +1448,7 @@ class ConstTopLevelVariableElementImpl extends TopLevelVariableElementImpl
  *
  * This class is not intended to be part of the public API for analyzer.
  */
-abstract class ConstVariableElement {
+abstract class ConstVariableElement implements ConstantEvaluationTarget {
   /**
    * If this element represents a constant variable, and it has an initializer,
    * a copy of the initializer for the constant.  Otherwise `null`.
@@ -1506,6 +1459,22 @@ abstract class ConstVariableElement {
    * initializers.
    */
   Expression constantInitializer;
+
+  @override
+  EvaluationResultImpl evaluationResult;
+
+  /**
+   * Return a representation of the value of this variable, forcing the value
+   * to be computed if it had not previously been computed, or `null` if either
+   * this variable was not declared with the 'const' modifier or if the value of
+   * this variable could not be computed because of errors.
+   */
+  DartObject computeConstantValue() {
+    if (evaluationResult == null) {
+      context?.computeResult(this, CONSTANT_VALUE);
+    }
+    return evaluationResult?.value;
+  }
 }
 
 /**
@@ -1514,11 +1483,6 @@ abstract class ConstVariableElement {
 class DefaultFieldFormalParameterElementImpl
     extends FieldFormalParameterElementImpl with ConstVariableElement {
   /**
-   * The result of evaluating this variable's initializer.
-   */
-  EvaluationResultImpl _result;
-
-  /**
    * Initialize a newly created parameter element to have the given [name] and
    * [nameOffset].
    */
@@ -1530,17 +1494,6 @@ class DefaultFieldFormalParameterElementImpl
    */
   DefaultFieldFormalParameterElementImpl.forNode(Identifier name)
       : super.forNode(name);
-
-  @override
-  DartObject get constantValue => _result?.value;
-
-  @override
-  EvaluationResultImpl get evaluationResult => _result;
-
-  @override
-  void set evaluationResult(EvaluationResultImpl result) {
-    this._result = result;
-  }
 }
 
 /**
@@ -1549,11 +1502,6 @@ class DefaultFieldFormalParameterElementImpl
 class DefaultParameterElementImpl extends ParameterElementImpl
     with ConstVariableElement {
   /**
-   * The result of evaluating this variable's initializer.
-   */
-  EvaluationResultImpl _result;
-
-  /**
    * Initialize a newly created parameter element to have the given [name] and
    * [nameOffset].
    */
@@ -1566,17 +1514,6 @@ class DefaultParameterElementImpl extends ParameterElementImpl
   DefaultParameterElementImpl.forNode(Identifier name) : super.forNode(name);
 
   @override
-  DartObject get constantValue => _result?.value;
-
-  @override
-  EvaluationResultImpl get evaluationResult => _result;
-
-  @override
-  void set evaluationResult(EvaluationResultImpl result) {
-    this._result = result;
-  }
-
-  @override
   DefaultFormalParameter computeNode() =>
       getNodeMatching((node) => node is DefaultFormalParameter);
 }
@@ -1772,6 +1709,14 @@ class ElementAnnotationImpl implements ElementAnnotation {
   Source get source => compilationUnit.source;
 
   @override
+  DartObject computeConstantValue() {
+    if (evaluationResult == null) {
+      context?.computeResult(this, CONSTANT_VALUE);
+    }
+    return constantValue;
+  }
+
+  @override
   String toString() => '@$element';
 }
 
@@ -4948,7 +4893,7 @@ abstract class VariableElementImpl extends ElementImpl
   Expression get constantInitializer => null;
 
   @override
-  DartObject get constantValue => null;
+  DartObject get constantValue => evaluationResult?.value;
 
   /**
    * Return the result of evaluating this variable's initializer as a
@@ -5021,6 +4966,9 @@ abstract class VariableElementImpl extends ElementImpl
   }
 
   @override
+  DartObject computeConstantValue() => null;
+
+  @override
   void visitChildren(ElementVisitor visitor) {
     super.visitChildren(visitor);
     _initializer?.accept(visitor);