Ignore PathNotFoundException when watching subdirs

pkgs/watcher/CHANGELOG.md

@@ -1,3 +1,9 @@
+## 1.1.4-wip
+
+- Improve handling of subdirectories on Linux: ignore `PathNotFoundException`
+  due to subdirectory deletion during watch setup, instead of raising it on the
+  event stream.
+
 ## 1.1.3
 
 - Improve handling of
@@ -6,7 +12,7 @@
   events. But, the restart would sometimes silently fail. Now, it is more
   reliable.
 - Improving handling of directories that are created then immediately deleted on
-  Windows. Previously, that could cause a `PathNotfoundException` to be thrown.
+  Windows. Previously, that could cause a `PathNotFoundException` to be thrown.
 
 ## 1.1.2
 

pkgs/watcher/lib/src/directory_watcher/linux.dart

@@ -136,10 +136,17 @@ class _LinuxDirectoryWatcher
     // top-level clients such as barback as well, and could be implemented with
     // a wrapper similar to how listening/canceling works now.
 
-    // TODO(nweiz): Catch any errors here that indicate that the directory in
-    // question doesn't exist and silently stop watching it instead of
-    // propagating the errors.
-    var stream = Directory(path).watch();
+    var stream = Directory(path).watch().transform(
+        StreamTransformer<FileSystemEvent, FileSystemEvent>.fromHandlers(
+      handleError: (error, st, sink) {
+        // Directory might no longer exist at the point where we try to
+        // start the watcher. Simply ignore this error and let the stream
+        // close.
+        if (error is! PathNotFoundException) {
+          sink.addError(error, st);
+        }
+      },
+    ));
     _subdirStreams[path] = stream;
     _nativeEvents.add(stream);
   }

pkgs/watcher/pubspec.yaml

@@ -1,5 +1,5 @@
 name: watcher
-version: 1.1.3
+version: 1.1.4-wip
 description: >-
   A file system watcher. It monitors changes to contents of directories and
   sends notifications when files have been added, removed, or modified.

pkgs/watcher/test/directory_watcher/shared.dart

@@ -1,8 +1,11 @@
 // Copyright (c) 2012, 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 'dart:io' as io;
+import 'dart:isolate';
 
 import 'package:test/test.dart';
+import 'package:test_descriptor/test_descriptor.dart' as d;
 import 'package:watcher/src/utils.dart';
 
 import '../utils.dart';
@@ -340,5 +343,31 @@ void sharedTests() {
       events.add(isRemoveEvent('dir/sub'));
       await inAnyOrder(events);
     });
+
+    test('subdirectory watching is robust against races', () async {
+      // Make sandboxPath accessible to child isolates created by Isolate.run.
+      final sandboxPath = d.sandbox;
+      final dirNames = [for (var i = 0; i < 50; i++) 'dir$i'];
+      await startWatcher();
+
+      // Repeatedly create and delete subdirectories in attempt to trigger
+      // a race.
+      for (var i = 0; i < 10; i++) {
+        for (var dir in dirNames) {
+          createDir(dir);
+        }
+        await Isolate.run(() async {
+          await Future.wait([
+            for (var dir in dirNames)
+              io.Directory('$sandboxPath/$dir').delete(),
+          ]);
+        });
+      }
+
+      writeFile('a/b/c/d/file.txt');
+      await inAnyOrder([
+        isAddEvent('a/b/c/d/file.txt'),
+      ]);
+    });
   });
 }