Add a --poll option (#390)

Partially addresses #264.

Author: nex3

CHANGELOG.md

@@ -1,3 +1,10 @@
+## 1.8.0
+
+### Command-Line Interface
+
+* Add a `--poll` flag to make `--watch` mode repeatedly check the filesystem for
+  updates rather than relying on native filesystem notifications.
+
 ## 1.7.3
 
 * No user-visible changes.

lib/src/executable/options.dart

@@ -75,6 +75,10 @@ class ExecutableOptions {
       ..addFlag('watch',
           help: 'Watch stylesheets and recompile when they change.',
           negatable: false)
+      ..addFlag('poll',
+          help: 'Manually check for changes rather than using a native '
+              'watcher.\n'
+              'Only valid with --watch.')
       ..addFlag('interactive',
           abbr: 'i',
           help: 'Run an interactive SassScript shell.',
@@ -170,6 +174,9 @@ class ExecutableOptions {
   /// Whether to continuously watch the filesystem for changes.
   bool get watch => _options['watch'] as bool;
 
+  /// Whether to manually poll for changes when watching.
+  bool get poll => _options['poll'] as bool;
+
   /// A map from source paths to the destination paths where the compiled CSS
   /// should be written.
   ///
@@ -380,7 +387,11 @@ class ExecutableOptions {
     }
   }
 
-  ExecutableOptions._(this._options);
+  ExecutableOptions._(this._options) {
+    if (_options.wasParsed('poll') && !watch) {
+      _fail("--poll may not be passed without --watch.");
+    }
+  }
 
   /// Makes [url] absolute or relative (to the directory containing
   /// [destination]) according to the `source-map-urls` option.

lib/src/executable/watch.dart

@@ -25,7 +25,7 @@ Future watch(ExecutableOptions options, StylesheetGraph graph) async {
     ..addAll(options.sourcesToDestinations.keys.map(p.dirname))
     ..addAll(options.loadPaths);
 
-  var dirWatcher = new MultiDirWatcher();
+  var dirWatcher = new MultiDirWatcher(poll: options.poll);
   await Future.wait(directoriesToWatch.map((dir) {
     // If a directory doesn't exist, watch its parent directory so that we're
     // notified once it starts existing.

lib/src/io/interface.dart

@@ -87,4 +87,7 @@ int exitCode;
 /// Returns a future that completes with a single-subscription stream once the
 /// directory has been scanned initially. The watch is canceled when the stream
 /// is closed.
-Future<Stream<WatchEvent>> watchDir(String path) => null;
+///
+/// If [poll] is `true`, this manually checks the filesystem for changes
+/// periodically rather than using a native filesystem monitoring API.
+Future<Stream<WatchEvent>> watchDir(String path, {bool poll: false}) => null;

lib/src/io/node.dart

@@ -239,9 +239,9 @@ external int get exitCode;
 @JS("process.exitCode")
 external set exitCode(int code);
 
-Future<Stream<WatchEvent>> watchDir(String path) {
-  var watcher =
-      chokidar.watch(path, new ChokidarOptions(disableGlobbing: true));
+Future<Stream<WatchEvent>> watchDir(String path, {bool poll: false}) {
+  var watcher = chokidar.watch(
+      path, new ChokidarOptions(disableGlobbing: true, usePolling: poll));
 
   // Don't assign the controller until after the ready event fires. Otherwise,
   // Chokidar will give us a bunch of add events for files that already exist.

lib/src/io/vm.dart

@@ -74,8 +74,9 @@ DateTime modificationTime(String path) {
   return stat.modified;
 }
 
-Future<Stream<WatchEvent>> watchDir(String path) async {
-  var watcher = new DirectoryWatcher(path);
+Future<Stream<WatchEvent>> watchDir(String path, {bool poll: false}) async {
+  var watcher =
+      poll ? new PollingDirectoryWatcher(path) : new DirectoryWatcher(path);
 
   // Wrap [stream] in a [SubscriptionStream] so that its `onListen` event
   // triggers but the caller can still listen at their leisure.

lib/src/node/chokidar.dart

@@ -16,8 +16,9 @@ class Chokidar {
 @anonymous
 class ChokidarOptions {
   external bool get disableGlobbing;
+  external bool get usePolling;
 
-  external factory ChokidarOptions({bool disableGlobbing});
+  external factory ChokidarOptions({bool disableGlobbing, bool usePolling});
 }
 
 @JS()

lib/src/util/multi_dir_watcher.dart

@@ -24,6 +24,15 @@ class MultiDirWatcher {
   Stream<WatchEvent> get events => _group.stream;
   final _group = new StreamGroup<WatchEvent>();
 
+  /// Whether to manually check the filesystem for changes periodically.
+  final bool _poll;
+
+  /// Creates a [MultiDirWatcher].
+  ///
+  /// If [poll] is `true`, this manually checks the filesystem for changes
+  /// periodically rather than using a native filesystem monitoring API.
+  MultiDirWatcher({bool poll: false}) : _poll = poll;
+
   /// Watches [directory] for changes.
   ///
   /// Returns a [Future] that completes when [events] is ready to emit events
@@ -43,7 +52,7 @@ class MultiDirWatcher {
       }
     }
 
-    var future = watchDir(directory);
+    var future = watchDir(directory, poll: _poll);
     var stream = StreamCompleter.fromFuture(future);
     _watchers[directory] = stream;
     _group.add(stream);

pubspec.yaml

@@ -1,5 +1,5 @@
 name: sass
-version: 1.7.3
+version: 1.8.0-dev
 description: A Sass implementation in Dart.
 author: Dart Team <[email protected]>
 homepage: https://github.com/sass/dart-sass