Add a task to the new task model for computing constant values.

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index 4af7107afd9b21229a60e4d75d9ba3858dcd9ef1..23c6d8f0a03357fbb61ae8665a608a03bec2c26f 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -177,6 +177,13 @@ final ResultDescriptor<LibraryElement> LIBRARY_ELEMENT3 =
         cachingPolicy: ELEMENT_CACHING_POLICY);
 
 /**
+ * An [Element] that has been successfully constant-evaluated.
+ *
+ * TODO(paulberry): is ELEMENT_CACHING_POLICY the correct caching policy?

[Brian Wilkerson, 2015/05/08 19:22:38]

Long term, probably not. But I don't think it will hurt anything today.

[Paul Berry, 2015/05/08 19:44:22]

Ok, I will leave the TODO message as a reminder to revisit the question.

+ */
+final ResultDescriptor<Element> CONSTANT_EVALUATED_ELEMENT = new ResultDescriptor<Element>('CONST_EVALUATED_ELEMENT', null, cachingPolicy: ELEMENT_CACHING_POLICY);

[Brian Wilkerson, 2015/05/08 19:22:38]

Perhaps format the file?

[Paul Berry, 2015/05/08 19:44:22]

Done.

+
+/**
  * The partial [LibraryElement] associated with a library.
  *
  * In addition to [LIBRARY_ELEMENT3] the [LibraryElement.entryPoint] is set,
@@ -1612,9 +1619,70 @@ class BuildTypeProviderTask extends SourceBasedAnalysisTask {
 }
 
 /**
+ * A task that computes the value of a constant ([CONSTANT_EVALUATED_ELEMENT]) and
+ * stores it in the element model.
+ */
+class ComputeConstantValueTask extends ElementBasedAnalysisTask {
+  /**
+   * The name of the input which ensures that dependent constants are evaluated
+   * before the target.
+   */
+  static const String DEPENDENCIES_INPUT = 'DEPENDENCIES_INPUT';
+
+  static final TaskDescriptor DESCRIPTOR = new TaskDescriptor('ComputeConstantValueTask',
+      createTask, buildInputs, <ResultDescriptor>[CONSTANT_EVALUATED_ELEMENT]);
+
+  ComputeConstantValueTask(InternalAnalysisContext context, Element element)
+      : super(context, element);
+
+  @override
+  TaskDescriptor get descriptor => DESCRIPTOR;
+
+  @override
+  void internalPerform() {
+    //
+    // Prepare inputs.
+    //
+    // Note: DEPENDENCIES_INPUT is not needed.  It is merely a bookkeeping
+    // dependency to ensure that the constants that this constant depends on
+    // are computed first.

[scheglov, 2015/05/08 18:46:07]

Should this comment be removed?

[Paul Berry, 2015/05/08 19:44:22]

I think it should stay.  I was trying to explain why it's not necessary for the
task to access inputs[DEPENDENCIES_INPUT].

+    Element element = target;
+    AnalysisContext context = element.context;
+    TypeProvider typeProvider = context.typeProvider;
+    //
+    // Compute the value of the constant.
+    //
+    new ConstantEvaluationEngine(typeProvider, context.declaredVariables).computeConstantValue(element);
+    //
+    // Record outputs.
+    //
+    outputs[CONSTANT_EVALUATED_ELEMENT] = element;
+  }
+
+  /**
+   * Return a map from the names of the inputs of this kind of task to the task
+   * input descriptors describing those inputs for a task with the given
+   * [target].
+   */
+  static Map<String, TaskInput> buildInputs(Element target) {
+    return <String, TaskInput>{
+      DEPENDENCIES_INPUT: CONSTANT_DEPENDENCIES.of(target).toListOf(CONSTANT_EVALUATED_ELEMENT)
+    };
+  }
+
+  /**
+   * Create a [ComputeConstantValueTask] based on the given [target] in the
+   * given [context].
+   */
+  static ComputeConstantValueTask createTask(AnalysisContext context, AnalysisTarget target) {
+    return new ComputeConstantValueTask(context, target);
+  }
+}
+
+/**
  * A task that computes [CONSTANT_DEPENDENCIES] for a constant.
  */
-class ComputeConstantDependenciesTask extends AnalysisTask {
+class ComputeConstantDependenciesTask extends ElementBasedAnalysisTask {
   /**
    * The name of the [RESOLVED_UNIT] input.
    */
@@ -1625,15 +1693,8 @@ class ComputeConstantDependenciesTask extends AnalysisTask {
       <ResultDescriptor>[CONSTANT_DEPENDENCIES]);
 
   ComputeConstantDependenciesTask(
-      InternalAnalysisContext context, AnalysisTarget target)
-      : super(context, target);
-
-  @override
-  String get description {
-    Source source = target.source;
-    String sourceName = source == null ? '<unknown source>' : source.fullName;
-    return '${descriptor.name} for element $target in source $sourceName';
-  }
+      InternalAnalysisContext context, Element element)
+      : super(context, element);
 
   @override
   TaskDescriptor get descriptor => DESCRIPTOR;