Improvements to task model

pkg/analyzer/lib/task/model.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.task.model;
 
 import 'dart:collection';
 
 import 'package:analyzer/src/generated/engine.dart' hide AnalysisTask;
 import 'package:analyzer/src/generated/java_engine.dart';
@@ skipping 77 matching lines @@
    * [context] in order to produce results for the given [target].
    */
   AnalysisTask(this.context, this.target);
 
   /**
    * Return a textual description of this task.
    */
   String get description;
 
   /**
+   * Return the descriptor that describes this task.
+   */
+  TaskDescriptor get descriptor;
+
+  /**
+   * Return the value of the input with the given [name]. Throw an exception if
+   * the input value is not defined.
+   */
+  Object getRequiredInput(String name) {
+    if (inputs == null || !inputs.containsKey(name)) {
+      throw new AnalysisException("Could not $description: missing $name");
+    }
+    return inputs[name];
+  }
+
+  /**
+   * Return the source associated with the target. Throw an exception if
+   * the target is not associated with a source.
+   */
+  Source getRequiredSource() {
+    Source source = target.source;
+    if (source == null) {
+      throw new AnalysisException("Could not $description: missing source");
+    }
+    return source;
+  }
+
+  /**
    * Perform this analysis task, protected by an exception handler.
    *
    * This method should throw an [AnalysisException] if an exception occurs
    * while performing the task. If other kinds of exceptions are thrown they
    * will be wrapped in an [AnalysisException].
    *
    * If no exception is thrown, this method must fully populate the [outputs]
    * map (have a key/value pair for each result that this task is expected to
    * produce).
    */
@@ skipping 52 matching lines @@
 /**
  * A [ResultDescriptor] that denotes an analysis result that is a union of
  * one or more other results.
  *
  * Clients are not expected to subtype this class.
  */
 abstract class ContributionPoint<V> extends ResultDescriptor<V> {
   /**
    * Initialize a newly created contribution point to have the given [name].
    */
-  factory ContributionPoint(String name) = ContributionPointImpl;
+  factory ContributionPoint(String name, V defaultValue) =
+      ContributionPointImpl;
 
   /**
    * Return a list containing the descriptors of the results that are unioned
    * together to comprise the value of this result.
    *
    * Clients must not modify the returned list.
    */
   List<ResultDescriptor<V>> get contributors;
 }
 
 /**
  * A description of an analysis result that can be computed by an [AnalysisTask].
  *
  * Clients are not expected to subtype this class.
  */
 abstract class ResultDescriptor<V> {
   /**
    * Initialize a newly created analysis result to have the given [name]. If a
    * contribution point is specified, then this result will contribute to it.
    */
-  factory ResultDescriptor(String name, {ContributionPoint<V> contributesTo}) =
-      ResultDescriptorImpl;
+  factory ResultDescriptor(String name, V defaultValue,
+      {ContributionPoint<V> contributesTo}) = ResultDescriptorImpl;
+
+  /**
+   * Return the default value for results described by this descriptor.
+   */
+  V get defaultValue;
 
   /**
    * Return a task input that can be used to compute this result for the given
    * [target].
    */
   TaskInput<V> inputFor(AnalysisTarget target);
 }
 
 /**
  * A description of an [AnalysisTask].
@@ skipping 91 matching lines @@
    * be computed, or `false` if the inputs have been computed.
    *
    * It is safe to invoke [moveNext] after it has returned `false`. In this case
    * [moveNext] has no effect and will again return `false`.
    *
    * Throws a [StateError] if the value of the current result has not been
    * provided using [currentValue].
    */
   bool moveNext();
 }