Addressed Copilot review comments

Author: svick

src/libraries/Microsoft.Extensions.FileProviders.Physical/src/PhysicalFilesWatcher.cs

@@ -39,7 +39,8 @@ public class PhysicalFilesWatcher : IDisposable
         // inside _root (which is below the FSW's watched path) are observed.
         private readonly bool _fileWatcherIsAboveRoot;
         // Number of currently registered tokens whose pattern requires watching subdirectories.
-        // Maintained as tokens are added and removed so we don't iterate the lookups.
+        // Maintained as tokens are added and removed so we don't iterate the lookups when
+        // re-evaluating IncludeSubdirectories.
         private int _subdirectoryRequiringTokenCount;
 
         // A single non-recursive watcher used when _root does not exist.
@@ -127,9 +128,6 @@ public PhysicalFilesWatcher(
                 }
 
                 _fileWatcher = fileSystemWatcher;
-                // IncludeSubdirectories is set in TryEnableFileSystemWatcher based on whether
-                // any registered token's pattern actually requires watching subdirectories.
-                _fileWatcher.IncludeSubdirectories = false;
                 _fileWatcher.Created += OnChanged;
                 _fileWatcher.Changed += OnChanged;
                 _fileWatcher.Renamed += OnRenamed;
@@ -389,7 +387,8 @@ void CancelAll(ConcurrentDictionary<string, ChangeTokenInfo> tokens, Func<string
                     {
                         if (requiresSubdirectories(entry.Key))
                         {
-                            Interlocked.Decrement(ref _subdirectoryRequiringTokenCount);
+                            int newCount = Interlocked.Decrement(ref _subdirectoryRequiringTokenCount);
+                            Debug.Assert(newCount >= 0, "Subdirectory-requiring token counter went negative.");
                         }
 
                         CancelToken(matchInfo);
@@ -454,7 +453,8 @@ private void ReportChangeForMatchedEntries(string path)
             {
                 if (FilePathRequiresSubdirectories(path))
                 {
-                    Interlocked.Decrement(ref _subdirectoryRequiringTokenCount);
+                    int newCount = Interlocked.Decrement(ref _subdirectoryRequiringTokenCount);
+                    Debug.Assert(newCount >= 0, "Subdirectory-requiring token counter went negative.");
                 }
 
                 CancelToken(matchInfo);
@@ -469,7 +469,8 @@ private void ReportChangeForMatchedEntries(string path)
                 {
                     if (WildcardRequiresSubdirectories(wildCardEntry.Key))
                     {
-                        Interlocked.Decrement(ref _subdirectoryRequiringTokenCount);
+                        int newCount = Interlocked.Decrement(ref _subdirectoryRequiringTokenCount);
+                        Debug.Assert(newCount >= 0, "Subdirectory-requiring token counter went negative.");
                     }
 
                     CancelToken(matchInfo);
@@ -535,6 +536,14 @@ private void TryDisableFileSystemWatcher()
                         // Perf: Turn off the file monitoring if no files or directories to monitor.
                         _fileWatcher.EnableRaisingEvents = false;
                     }
+                    else if (_fileWatcher.IncludeSubdirectories &&
+                        !_fileWatcherIsAboveRoot &&
+                        Volatile.Read(ref _subdirectoryRequiringTokenCount) == 0)
+                    {
+                        // Perf: Some tokens were removed and none of the remaining ones require
+                        // subdirectory watching, so we can stop recursing.
+                        _fileWatcher.IncludeSubdirectories = false;
+                    }
                 }
             }
 

src/libraries/Microsoft.Extensions.FileProviders.Physical/tests/PhysicalFilesWatcherTests.cs

@@ -119,14 +119,13 @@ public void IncludeSubdirectories_DowngradedWhenSubdirectoryPatternRemoved()
             using var fileSystemWatcher = new MockFileSystemWatcher(root.Path);
             using var physicalFilesWatcher = new PhysicalFilesWatcher(root.Path, fileSystemWatcher, pollForChanges: false);
 
+            physicalFilesWatcher.CreateFileChangeToken("appsettings.json");
             physicalFilesWatcher.CreateFileChangeToken("sub/file.json");
             Assert.True(fileSystemWatcher.IncludeSubdirectories);
 
             // Fire an event matching the subdirectory token to remove it from the lookup.
+            // The remaining root-only token does not require subdirectory watching, IncludeSubdirectories should be downgraded.
             fileSystemWatcher.CallOnChanged(new FileSystemEventArgs(WatcherChangeTypes.Changed, root.Path, "sub/file.json"));
-
-            // Adding a new root-only token re-evaluates IncludeSubdirectories.
-            physicalFilesWatcher.CreateFileChangeToken("appsettings.json");
             Assert.False(fileSystemWatcher.IncludeSubdirectories);
         }
 
@@ -145,10 +144,6 @@ public void IncludeSubdirectories_NotDowngradedWhileSubdirectoryPatternRemains()
             // Remove only the root-level token; the subdirectory token must keep subdirectories enabled.
             fileSystemWatcher.CallOnChanged(new FileSystemEventArgs(WatcherChangeTypes.Changed, root.Path, "appsettings.json"));
             Assert.True(fileSystemWatcher.IncludeSubdirectories);
-
-            // Trigger re-evaluation by adding another root-only token.
-            physicalFilesWatcher.CreateFileChangeToken("other.json");
-            Assert.True(fileSystemWatcher.IncludeSubdirectories);
         }
 
         [Fact]
@@ -166,9 +161,6 @@ public void IncludeSubdirectories_NotDowngradedWhenWildcardSubdirectoryPatternRe
             // Remove the root-level token; the recursive wildcard token must keep subdirectories enabled.
             fileSystemWatcher.CallOnChanged(new FileSystemEventArgs(WatcherChangeTypes.Changed, root.Path, "appsettings.json"));
             Assert.True(fileSystemWatcher.IncludeSubdirectories);
-
-            physicalFilesWatcher.CreateFileChangeToken("other.json");
-            Assert.True(fileSystemWatcher.IncludeSubdirectories);
         }
 
         [Fact]
@@ -188,6 +180,29 @@ public void IncludeSubdirectories_AlwaysTrueWhenWatcherIsAboveRoot()
             Assert.True(fsw.IncludeSubdirectories);
         }
 
+        [Fact]
+        [SkipOnPlatform(TestPlatforms.Browser | TestPlatforms.iOS | TestPlatforms.tvOS, "System.IO.FileSystem.Watcher is not supported on Browser/iOS/tvOS")]
+        public async Task IncludeSubdirectories_StarPatternIsNotRecursive_DoesNotMatchSubdirectoryFile()
+        {
+            using var root = new TempDirectory(GetTestFilePath());
+            using var fileSystemWatcher = new MockFileSystemWatcher(root.Path);
+            using var physicalFilesWatcher = new PhysicalFilesWatcher(root.Path, fileSystemWatcher, pollForChanges: false);
+
+            IChangeToken token = physicalFilesWatcher.CreateFileChangeToken("*.json");
+            Assert.False(fileSystemWatcher.IncludeSubdirectories);
+
+            Task changed = WhenChanged(token);
+
+            // A '*' pattern should not match files in subdirectories.
+            fileSystemWatcher.CallOnChanged(new FileSystemEventArgs(WatcherChangeTypes.Changed, root.Path, "sub/foo.json"));
+            await Task.Delay(WaitTimeForTokenToFire);
+            Assert.False(changed.IsCompleted, "Token must not fire for an event in a subdirectory.");
+
+            // Sanity check: a root-level event does fire the token.
+            fileSystemWatcher.CallOnChanged(new FileSystemEventArgs(WatcherChangeTypes.Changed, root.Path, "foo.json"));
+            await changed;
+        }
+
         [Fact]
         [SkipOnPlatform(TestPlatforms.Browser | TestPlatforms.iOS | TestPlatforms.tvOS, "System.IO.FileSystem.Watcher is not supported on Browser/iOS/tvOS")]
         public void CreateFileChangeToken_DoesNotAllowPathsAboveRoot()