Fix computation of errors to not run extra tasks

pkg/analyzer/lib/src/task/inputs.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.src.task.inputs;
 
 import 'dart:collection';
 
 import 'package:analyzer/task/model.dart';
 
 /**
  * A function that converts an object of the type [B] into a [TaskInput].
  * This is used, for example, by a [ListToListTaskInput] to create task inputs
  * for each value in a list of values.
  */
 typedef TaskInput<E> GenerateTaskInputs<B, E>(B object);
 
 /**
  * A function that maps one [value] to another value.
  */
 typedef R Mapper<P, R>(P value);
 
 /**
  * An input to an [AnalysisTask] that is computed by accessing a single result
  * defined on a single target.
  */
+class ConstantTaskInput<V> extends TaskInputImpl<V> {
+  final V value;
+
+  ConstantTaskInput(this.value);
+
+  @override
+  TaskInputBuilder<V> createBuilder() {
+    return new ConstantTaskInputBuilder<V>(this);
+  }
+}
+
+/**
+ * A [TaskInputBuilder] used to build an input based on a [ConstantTaskInput].
+ */
+class ConstantTaskInputBuilder<V> implements TaskInputBuilder<V> {
+  final ConstantTaskInput input;
+
+  ConstantTaskInputBuilder(this.input);
+
+  @override
+  ResultDescriptor get currentResult => null;
+
+  @override
+  AnalysisTarget get currentTarget => null;
+
+  @override
+  void set currentValue(Object value) {
+    throw new StateError('Only supported after moveNext() returns true');
+  }
+
+  @override
+  V get inputValue => input.value;
+
+  @override
+  void currentValueNotAvailable() {
+    throw new StateError('Only supported after moveNext() returns true');
+  }
+
+  @override
+  bool moveNext() => false;
+}
+
+/**
+ * An input to an [AnalysisTask] that is computed by accessing a single result
+ * defined on a single target.
+ */
 class ListTaskInputImpl<E> extends SimpleTaskInput<List<E>>
     with ListTaskInputMixin<E>
     implements ListTaskInput<E> {
   /**
    * Initialize a newly created task input that computes the input by accessing
    * the given [result] associated with the given [target].
    */
   ListTaskInputImpl(AnalysisTarget target, ResultDescriptor<List<E>> result)
       : super(target, result);
 }
@@ skipping 631 matching lines @@
       if (currentBuilder.inputValue != null) {
         inputs[_currentName] = currentBuilder.inputValue;
       }
       nameIndex++;
     }
     if (nameIndex >= inputNames.length) {
       // There is no next value, so we're done.
       return false;
     }
     currentBuilder = inputDescriptors[_currentName].createBuilder();
-    // NOTE: This assumes that every builder will require at least one result
-    // value to be created. If that assumption is every broken, this method will
-    // need to be changed to advance until we find a builder that does require
-    // a result to be computed (or run out of builders).
-    return currentBuilder.moveNext();
+    while (!currentBuilder.moveNext()) {
+      if (currentBuilder.inputValue != null) {
+        inputs[_currentName] = currentBuilder.inputValue;
+      }
+      nameIndex++;
+      if (nameIndex >= inputNames.length) {
+        // There is no next value, so we're done.
+        return false;
+      }
+      currentBuilder = inputDescriptors[_currentName].createBuilder();
+    }
+    return true;

[scheglov, 2015/09/29 21:55:32]

Too bad that we have to duplicate logic here :-(

[Brian Wilkerson, 2015/09/29 22:11:00]

Agreed. I couldn't think of a good way to restructure the code to avoid it, but
I'll look again. Meanwhile, I'll add some tests.

   }
 }
 
 /**
  * An input to an [AnalysisTask] that is computed by the following steps. First
  * another (base) task input is used to compute a [List]-valued result. An input
  * generator function is then used to map each element of that list to a task
  * input. Finally, each of the task inputs are used to access analysis results,
  * and a collection of the analysis results is used as the input to the task.
  */
@@ skipping 141 matching lines @@
       return false;
     }
     _baseListElement = _baseList[_baseListIndex];
     currentBuilder = input.generateTaskInputs(_baseListElement).createBuilder();
     return currentBuilder.moveNext();
   }
 
   void _addResultElement(B baseElement, E resultElement);
   void _initResultValue();
 }