Add support for implementing getAssists in plugins

pkg/analyzer_plugin/lib/utilities/assist/assist.dart

Index: pkg/analyzer_plugin/lib/utilities/assist/assist.dart
diff --git a/pkg/analyzer_plugin/lib/utilities/assist/assist.dart b/pkg/analyzer_plugin/lib/utilities/assist/assist.dart
new file mode 100644
index 0000000000000000000000000000000000000000..e68db53eb5076a27d6e6784c9718eebbc51d9c8b
--- /dev/null
+++ b/pkg/analyzer_plugin/lib/utilities/assist/assist.dart
@@ -0,0 +1,103 @@
+// 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_generated.dart';
+import 'package:analyzer_plugin/src/utilities/assist/assist.dart';
+import 'package:analyzer_plugin/utilities/generator.dart';
+
+/**
+ * An object that [AssistContributor]s use to record assists.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class AssistCollector {
+  /**
+   * Record a new [assist].
+   */
+  void addAssist(PrioritizedSourceChange assist);
+}
+
+/**
+ * An object used to produce assists.
+ *
+ * Clients may implement this class when implementing plugins.
+ */
+abstract class AssistContributor {
+  /**
+   * Contribute assists for the location in the file specified by the given
+   * [request] into the given [collector].
+   */
+  void computeFixes(AssistRequest request, AssistCollector collector);

[scheglov, 2017/06/07 16:09:19]

computeAssists() ?

+}
+
+/**
+ * A generator that will generate an 'edit.getAssists' response.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+class AssistGenerator {
+  /**
+   * The contributors to be used to generate the assists.
+   */
+  final List<AssistContributor> contributors;
+
+  /**
+   * Initialize a newly created assists generator to use the given
+   * [contributors].
+   */
+  AssistGenerator(this.contributors);
+
+  /**
+   * Create an 'edit.getAssists' response for the location in the file specified
+   * by the given [request]. If any of the contributors throws an exception,
+   * also create a non-fatal 'plugin.error' notification.
+   */
+  GeneratorResult generateAssistsResponse(AssistRequest request) {
+    List<Notification> notifications = <Notification>[];
+    AssistCollectorImpl collector = new AssistCollectorImpl();
+    for (AssistContributor contributor in contributors) {
+      try {
+        contributor.computeFixes(request, collector);
+      } catch (exception, stackTrace) {
+        notifications.add(new PluginErrorParams(
+                false, exception.toString(), stackTrace.toString())
+            .toNotification());
+      }
+    }
+    EditGetAssistsResult result = new EditGetAssistsResult(collector.assists);
+    return new GeneratorResult(result, notifications);
+  }
+}
+
+/**
+ * The information about a requested set of assists.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class AssistRequest {
+  /**
+   * Return the length of the selection within the source for which assists are
+   * being requested.
+   */
+  int get length;
+
+  /**
+   * Return the offset of the selection within the source for which assists are
+   * being requested.
+   */
+  int get offset;
+
+  /**
+   * Return the resource provider associated with this request.
+   */
+  ResourceProvider get resourceProvider;
+
+  /**
+   * The analysis result for the file in which the assists are being requested.
+   */
+  ResolveResult get result;
+}