Don't follow symlinks when creating a DirectoryWatcher.

pkgs/watcher/CHANGELOG.md

@@ -1,3 +1,12 @@
+## 2.0.0
+
+- Changes the behavior of the `DirectoryWatcher` so that it no longer follows
+  symlinks. On Linux, but not on MacOS or Windows, it used to watch directories
+  to which there was a symlink within the directory being watched. It no longer
+  does that. Code that depends on that behavior will need to be updated so that
+  it independently traverses the root directory, locating and resolving
+  symlinks, and watching any directories being linked to.
+
 ## 1.1.3
 
 - Improve handling of

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

@@ -92,7 +92,7 @@ class _LinuxDirectoryWatcher
     });
 
     _listen(
-      Directory(path).list(recursive: true),
+      Directory(path).list(recursive: true, followLinks: false),
       (FileSystemEntity entity) {
         if (entity is Directory) {
           _watchSubdir(entity.path);
@@ -228,7 +228,7 @@ class _LinuxDirectoryWatcher
 
   /// Emits [ChangeType.ADD] events for the recursive contents of [path].
   void _addSubdir(String path) {
-    _listen(Directory(path).list(recursive: true), (FileSystemEntity entity) {
+    _listen(Directory(path).list(recursive: true, followLinks: false), (FileSystemEntity entity) {
       if (entity is Directory) {
         _watchSubdir(entity.path);
       } else {

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

@@ -148,7 +148,7 @@ class _MacOSDirectoryWatcher
 
           if (_files.containsDir(path)) continue;
 
-          var stream = Directory(path).list(recursive: true);
+          var stream = Directory(path).list(recursive: true, followLinks: false);
           var subscription = stream.listen((entity) {
             if (entity is Directory) return;
             if (_files.contains(path)) return;
@@ -373,7 +373,7 @@ class _MacOSDirectoryWatcher
 
     _files.clear();
     var completer = Completer<void>();
-    var stream = Directory(path).list(recursive: true);
+    var stream = Directory(path).list(recursive: true, followLinks: false);
     _initialListSubscription = stream.listen((entity) {
       if (entity is! Directory) _files.add(entity.path);
     }, onError: _emitError, onDone: completer.complete, cancelOnError: true);

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

@@ -112,7 +112,7 @@ class _PollingDirectoryWatcher
       _filesToProcess.add(null);
     }
 
-    var stream = Directory(path).list(recursive: true);
+    var stream = Directory(path).list(recursive: true, followLinks: false);
     _listSubscription = stream.listen((entity) {
       assert(!_events.isClosed);
 

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

@@ -185,7 +185,7 @@ class _WindowsDirectoryWatcher
 
           if (_files.containsDir(path)) continue;
 
-          var stream = Directory(path).list(recursive: true);
+          var stream = Directory(path).list(recursive: true, followLinks: false);
           var subscription = stream.listen((entity) {
             if (entity is Directory) return;
             if (_files.contains(entity.path)) return;
@@ -435,7 +435,7 @@ class _WindowsDirectoryWatcher
 
     _files.clear();
     var completer = Completer<void>();
-    var stream = Directory(path).list(recursive: true);
+    var stream = Directory(path).list(recursive: true, followLinks: false);
     void handleEntity(FileSystemEntity entity) {
       if (entity is! Directory) _files.add(entity.path);
     }

pkgs/watcher/pubspec.yaml

@@ -1,5 +1,5 @@
 name: watcher
-version: 1.1.3
+version: 2.0.0
 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

@@ -341,4 +341,19 @@ void sharedTests() {
       await inAnyOrder(events);
     });
   });
+  group('symlinks', () {
+    test('are not watched when not enabled', () async {
+      writeFile('dir/sub/a.txt', contents: 'a');
+      writeFile('sibling/sub/b.txt', contents: '1');
+      writeSymlink('dir/linked', target: 'sibling');
+      await startWatcher(path: 'dir');
+
+      writeFile('sibling/sub/b.txt', contents: '2');
+      // Ensure that any events for the first modification arrive before the
+      // events for the second modification.
+      await pumpEventQueue();
+      writeFile('dir/sub/a.txt', contents: 'a');
+      await expectModifyEvent('dir/sub/a.txt');
+    });
+  });
 }

pkgs/watcher/test/utils.dart

@@ -267,6 +267,19 @@ void renameDir(String from, String to) {
 void deleteDir(String path) {
   Directory(p.join(d.sandbox, path)).deleteSync(recursive: true);
 }
+
+/// Schedules writing a symlink in the sandbox at [path] that links to [target].
+void writeSymlink(String path, {required String target}) {
+  var fullPath = p.join(d.sandbox, path);
+
+  // Create any needed subdirectories.
+  var dir = Directory(p.dirname(fullPath));
+  if (!dir.existsSync()) {
+    dir.createSync(recursive: true);
+  }
+
+  Link(fullPath).createSync(target);
+}
 
 /// Runs [callback] with every permutation of non-negative numbers for each
 /// argument less than [limit].