Add plugin support for occurrences (and fix typo)

pkg/analyzer_plugin/lib/utilities/occurrences/occurrences.dart

+// Copyright (c) 2017, 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.
+
+import 'package:analyzer/dart/analysis/results.dart';
+import 'package:analyzer/file_system/file_system.dart';
+import 'package:analyzer_plugin/protocol/protocol.dart';
+import 'package:analyzer_plugin/protocol/protocol_common.dart'
+    hide AnalysisError;
+import 'package:analyzer_plugin/protocol/protocol_generated.dart';
+import 'package:analyzer_plugin/src/utilities/occurrences/occurrences.dart';
+import 'package:analyzer_plugin/utilities/generator.dart';
+
+/**
+ * The information about a requested set of occurrences information when
+ * computing occurrences information in a `.dart` file.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class DartOccurrencesRequest implements OccurrencesRequest {
+  /**
+   * The analysis result for the file for which the occurrences information is
+   * being requested.
+   */
+  ResolveResult get result;
+}
+
+/**
+ * An object that [OccurrencesContributor]s use to record occurrences.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class OccurrencesCollector {
+  /**
+   * Add an occurrence of the given [element] at the given [offset].
+   */
+  void addOccurrence(Element element, int offset);
+}
+
+/**
+ * An object used to produce occurrences information.
+ *
+ * Clients may implement this class when implementing plugins.
+ */
+abstract class OccurrencesContributor {
+  /**
+   * Contribute occurrences information into the given [collector].
+   */
+  void computeOccurrences(
+      OccurrencesRequest request, OccurrencesCollector collector);
+}
+
+/**
+ * A generator that will generate an 'analysis.occurrences' notification.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+class OccurrencesGenerator {
+  /**
+   * The contributors to be used to generate the occurrences information.
+   */
+  final List<OccurrencesContributor> contributors;
+
+  /**
+   * Initialize a newly created occurrences generator to use the given
+   * [contributors].
+   */
+  OccurrencesGenerator(this.contributors);
+
+  /**
+   * Create an 'analysis.occurrences' notification. If any of the contributors
+   * throws an exception, also create a non-fatal 'plugin.error' notification.
+   */
+  GeneratorResult generateOccurrencesNotification(OccurrencesRequest request) {
+    List<Notification> notifications = <Notification>[];
+    OccurrencesCollectorImpl collector = new OccurrencesCollectorImpl();
+    for (OccurrencesContributor contributor in contributors) {
+      try {
+        contributor.computeOccurrences(request, collector);
+      } catch (exception, stackTrace) {
+        notifications.add(new PluginErrorParams(
+                false, exception.toString(), stackTrace.toString())
+            .toNotification());
+      }
+    }
+    notifications.add(
+        new AnalysisOccurrencesParams(request.path, collector.occurrences)
+            .toNotification());
+    return new GeneratorResult(null, notifications);
+  }
+}
+
+/**
+ * The information about a requested set of occurrences information.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class OccurrencesRequest {
+  /**
+   * Return the path of the file for which occurrences information is being
+   * requested.
+   */
+  String get path;
+
+  /**
+   * Return the resource provider associated with this request.
+   */
+  ResourceProvider get resourceProvider;
+}