Add folding support for plugins and update the main tutorial page

pkg/analyzer_plugin/lib/utilities/folding/folding.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/src/generated/source.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/folding/folding.dart';
+import 'package:analyzer_plugin/utilities/generator.dart';
+
+/**
+ * The information about a requested set of folding regions when computing
+ * folding regions in a `.dart` file.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class DartFoldingRequest implements FoldingRequest {
+  /**
+   * The analysis result for the file for which the folding regions are being
+   * requested.
+   */
+  ResolveResult get result;
+}
+
+/**
+ * An object that [FoldingContributor]s use to record folding regions.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class FoldingCollector {
+  /**
+   * Record a new folding region corresponding to the given [range] that has the
+   * given [kind].
+   */
+  void addRange(SourceRange range, FoldingKind kind);
+
+  /**
+   * Record a new folding region with the given [offset] and [length] that has
+   * the given [kind].
+   */
+  void addRegion(int offset, int length, FoldingKind kind);
+}
+
+/**
+ * An object used to produce folding regions.
+ *
+ * Clients may implement this class when implementing plugins.
+ */
+abstract class FoldingContributor {
+  /**
+   * Contribute folding regions into the given [collector].
+   */
+  void computeFolding(FoldingRequest request, FoldingCollector collector);
+}
+
+/**
+ * A generator that will generate an 'analysis.folding' notification.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+class FoldingGenerator {
+  /**
+   * The contributors to be used to generate the folding regions.
+   */
+  final List<FoldingContributor> contributors;
+
+  /**
+   * Initialize a newly created folding generator to use the given
+   * [contributors].
+   */
+  FoldingGenerator(this.contributors);
+
+  /**
+   * Create an 'analysis.folding' notification. If any of the contributors
+   * throws an exception, also create a non-fatal 'plugin.error' notification.
+   */
+  GeneratorResult generateFoldingNotification(FoldingRequest request) {
+    List<Notification> notifications = <Notification>[];
+    FoldingCollectorImpl collector = new FoldingCollectorImpl();
+    for (FoldingContributor contributor in contributors) {
+      try {
+        contributor.computeFolding(request, collector);
+      } catch (exception, stackTrace) {
+        notifications.add(new PluginErrorParams(
+                false, exception.toString(), stackTrace.toString())
+            .toNotification());
+      }
+    }
+    notifications.add(new AnalysisFoldingParams(request.path, collector.regions)
+        .toNotification());
+    return new GeneratorResult(null, notifications);
+  }
+}
+
+/**
+ * The information about a requested set of folding regions.
+ *
+ * Clients may not extend, implement or mix-in this class.
+ */
+abstract class FoldingRequest {
+  /**
+   * Return the path of the file for which folding regions are being requested.
+   */
+  String get path;
+
+  /**
+   * Return the resource provider associated with this request.
+   */
+  ResourceProvider get resourceProvider;
+}