Use memento in ScanDartTask.

pkg/analyzer/lib/src/task/dart.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.dart;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/src/generated/ast.dart';
@@ skipping 2365 matching lines @@
    * Create a [ResolveVariableReferencesTask] based on the given [target] in
    * the given [context].
    */
   static ResolveVariableReferencesTask createTask(
       AnalysisContext context, AnalysisTarget target) {
     return new ResolveVariableReferencesTask(context, target);
   }
 }
 
 /**
+ * The memento for [ScanDartTask].
+ */
+class ScanDartMemento {
+  final String content;
+  final Token tokenStream;
+  final LineInfo lineInfo;
+  final List<AnalysisError> errors;
+  ScanDartMemento(this.content, this.tokenStream, this.lineInfo, this.errors);
+}
+
+/**
  * A task that scans the content of a file, producing a set of Dart tokens.
  */
 class ScanDartTask extends SourceBasedAnalysisTask {
   /**
    * The name of the input whose value is the content of the file.
    */
   static const String CONTENT_INPUT_NAME = 'CONTENT_INPUT_NAME';
 
   /**
    * The task descriptor describing this kind of task.
@@ skipping 13 matching lines @@
       : super(context, target);
 
   @override
   TaskDescriptor get descriptor => DESCRIPTOR;
 
   @override
   void internalPerform() {
     Source source = getRequiredSource();
     String content = getRequiredInput(CONTENT_INPUT_NAME);
 
+    if (inputMemento is ScanDartMemento) {
+      ScanDartMemento memento = inputMemento;
+      if (memento.content == content) {
+        outputMemento = memento;
+        outputs[TOKEN_STREAM] = memento.tokenStream;
+        outputs[LINE_INFO] = memento.lineInfo;
+        outputs[SCAN_ERRORS] = memento.errors;
+        return;
+      }
+    }
+
     RecordingErrorListener errorListener = new RecordingErrorListener();
     Scanner scanner =
         new Scanner(source, new CharSequenceReader(content), errorListener);
     scanner.preserveComments = context.analysisOptions.preserveComments;
     scanner.enableNullAwareOperators =
         context.analysisOptions.enableNullAwareOperators;
-    outputs[TOKEN_STREAM] = scanner.tokenize();
-    outputs[LINE_INFO] = new LineInfo(scanner.lineStarts);
-    outputs[SCAN_ERRORS] = errorListener.getErrorsForSource(source);
+
+    Token tokenStream = scanner.tokenize();
+    LineInfo lineInfo = new LineInfo(scanner.lineStarts);
+    List<AnalysisError> errors = errorListener.errors;
+    outputs[TOKEN_STREAM] = tokenStream;
+    outputs[LINE_INFO] = lineInfo;
+    outputs[SCAN_ERRORS] = errors;
+    outputMemento = new ScanDartMemento(content, tokenStream, lineInfo, errors);
   }
 
   /**
    * 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
    * [source].
    */
   static Map<String, TaskInput> buildInputs(Source source) {
     return <String, TaskInput>{CONTENT_INPUT_NAME: CONTENT.of(source)};
   }
@@ skipping 169 matching lines @@
   @override
   bool moveNext() {
     if (_newSources.isEmpty) {
       return false;
     }
     currentTarget = _newSources.first;
     _newSources.remove(currentTarget);
     return true;
   }
 }