Analysis request `getReachableSources` (#24893).

pkg/analysis_server/lib/src/services/dependencies/reachable_source_collector.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 services.dependencies.reachable_source_collector;
+
+import 'dart:collection';
+
+import 'package:analyzer/src/generated/engine.dart';
+import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/task/dart.dart';
+
+/// Collects reachable sources.
+class ReachableSourceCollector {
+  final Map<String, List<String>> _sourceMap =
+      new HashMap<String, List<String>>();
+
+  final Source source;
+  final AnalysisContext context;
+  ReachableSourceCollector(this.source, this.context);
+
+  /// Collect reachable sources.
+  Map<String, List<String>> collectSources() {
+    // Play it safe in case we're passed a source with no context.
+    if (context != null) {
+      _addDependencies(source);
+    }
+    return _sourceMap;
+  }
+
+  void _addDependencies(Source source) {
+    String sourceUri = source?.uri?.toString();

[Brian Wilkerson, 2015/12/02 01:56:27]

nit: We don't need the null-aware operators if we test 'source' in
'collectSources'. Not sure whether there's enough of a performance penalty to
care, but it would make the code a little cleaner.

[pquitslund, 2015/12/02 16:40:22]

Except that this is called recursively...  My thinking is that a source (or it's
URI) could be null anywhere in the chain of dependencies.

[Brian Wilkerson, 2015/12/02 18:04:53]

That shouldn't be the case. IMPORTED_LIBRARIES and EXPORTED_LIBRARIES should
never contain nulls.

+
+    // Bail if the source or URI are null.
+    if (sourceUri == null) {

[Brian Wilkerson, 2015/12/02 01:56:27]

Similarly, we don't need this test.

[pquitslund, 2015/12/02 16:40:22]

See above.

FWIW: my rationale is based on doing a bunch of scurrying around to harden lint
rules that fell down in the face of unexpected null values.

+      return;
+    }
+
+    // Careful not to revisit.
+    if (_sourceMap[sourceUri] != null) {
+      return;
+    }
+
+    List<Source> sources = <Source>[];
+    sources.addAll(context.computeResult(source, IMPORTED_LIBRARIES));
+    sources.addAll(context.computeResult(source, EXPORTED_LIBRARIES));
+
+    _sourceMap[sourceUri] =
+        sources.map((source) => source.uri.toString()).toList();
+
+    sources.forEach((s) => _addDependencies(s));
+  }
+}