File watcher improvements (#45131)

Author: tmat

src/BuiltInTools/dotnet-watch/Browser/BrowserConnector.cs

@@ -96,7 +96,7 @@ public bool TryGetRefreshServer(ProjectGraphNode projectNode, [NotNullWhen(true)
         {
             lock (_serversGuard)
             {
-                return _servers.TryGetValue(projectNode, out server);
+                return _servers.TryGetValue(projectNode, out server) && server != null;
             }
         }
 

src/BuiltInTools/dotnet-watch/FileItem.cs

@@ -10,15 +10,12 @@ internal readonly record struct FileItem
 
         /// <summary>
         /// List of all projects that contain this file (does not contain duplicates).
-        /// Empty if <see cref="Change"/> is <see cref="ChangeKind.Add"/> and the
-        /// item has not been assigned to a project yet.
+        /// Empty if the item is added but not been assigned to a project yet.
         /// </summary>
         public required List<string> ContainingProjectPaths { get; init; }
 
         public string? StaticWebAssetPath { get; init; }
 
-        public ChangeKind Change { get; init; }
-
         public bool IsStaticFile => StaticWebAssetPath != null;
     }
 }

src/BuiltInTools/dotnet-watch/HotReload/CompilationHandler.cs

@@ -364,7 +364,7 @@ private async ValueTask DisplayResultsAsync(WatchHotReloadService.Updates update
             switch (updates.Status)
             {
                 case ModuleUpdateStatus.None:
-                    _reporter.Output("No C# changes to apply.");
+                    _reporter.Report(MessageDescriptor.NoHotReloadChangesToApply);
                     break;
 
                 case ModuleUpdateStatus.Ready:

src/BuiltInTools/dotnet-watch/HotReloadDotNetWatcher.cs

@@ -9,7 +9,9 @@ internal sealed class FileWatcher(IReporter reporter) : IDisposable
         private readonly Dictionary<string, IDirectoryWatcher> _watchers = [];
 
         private bool _disposed;
-        public event Action<string, ChangeKind>? OnFileChange;
+        public event Action<ChangedPath>? OnFileChange;
+
+        public bool SuppressEvents { get; set; }
 
         public void Dispose()
         {
@@ -62,6 +64,11 @@ public void WatchDirectories(IEnumerable<string> directories)
                 }
 
                 var newWatcher = FileWatcherFactory.CreateWatcher(directory);
+                if (newWatcher is EventBasedDirectoryWatcher eventBasedWatcher)
+                {
+                    eventBasedWatcher.Logger = message => reporter.Verbose(message);
+                }
+
                 newWatcher.OnFileChange += WatcherChangedHandler;
                 newWatcher.OnError += WatcherErrorHandler;
                 newWatcher.EnableRaisingEvents = true;
@@ -78,9 +85,12 @@ private void WatcherErrorHandler(object? sender, Exception error)
             }
         }
 
-        private void WatcherChangedHandler(object? sender, (string changedPath, ChangeKind kind) args)
+        private void WatcherChangedHandler(object? sender, ChangedPath change)
         {
-            OnFileChange?.Invoke(args.changedPath, args.kind);
+            if (!SuppressEvents)
+            {
+                OnFileChange?.Invoke(change);
+            }
         }
 
         private void DisposeWatcher(string directory)
@@ -98,45 +108,43 @@ private void DisposeWatcher(string directory)
         private static string EnsureTrailingSlash(string path)
             => (path is [.., var last] && last != Path.DirectorySeparatorChar) ? path + Path.DirectorySeparatorChar : path;
 
-        public Task<ChangedFile?> WaitForFileChangeAsync(Action? startedWatching, CancellationToken cancellationToken)
-           => WaitForFileChangeAsync(
-               changeFilter: (path, kind) => new ChangedFile(new FileItem() { FilePath = path, ContainingProjectPaths = [] }, kind),
-               startedWatching,
-               cancellationToken);
-
-        public Task<ChangedFile?> WaitForFileChangeAsync(IReadOnlyDictionary<string, FileItem> fileSet, Action? startedWatching, CancellationToken cancellationToken)
-            => WaitForFileChangeAsync(
-                changeFilter: (path, kind) => fileSet.TryGetValue(path, out var fileItem) ? new ChangedFile(fileItem, kind) : null,
+        public async Task<ChangedFile?> WaitForFileChangeAsync(IReadOnlyDictionary<string, FileItem> fileSet, Action? startedWatching, CancellationToken cancellationToken)
+        {
+            var changedPath = await WaitForFileChangeAsync(
+                acceptChange: change => fileSet.ContainsKey(change.Path),
                 startedWatching,
                 cancellationToken);
 
-        public async Task<ChangedFile?> WaitForFileChangeAsync(Func<string, ChangeKind, ChangedFile?> changeFilter, Action? startedWatching, CancellationToken cancellationToken)
+            return changedPath.HasValue ? new ChangedFile(fileSet[changedPath.Value.Path], changedPath.Value.Kind) : null;
+        }
+
+        public async Task<ChangedPath?> WaitForFileChangeAsync(Predicate<ChangedPath> acceptChange, Action? startedWatching, CancellationToken cancellationToken)
         {
-            var fileChangedSource = new TaskCompletionSource<ChangedFile?>(TaskCreationOptions.RunContinuationsAsynchronously);
+            var fileChangedSource = new TaskCompletionSource<ChangedPath?>(TaskCreationOptions.RunContinuationsAsynchronously);
             cancellationToken.Register(() => fileChangedSource.TrySetResult(null));
 
-            void FileChangedCallback(string path, ChangeKind kind)
+            void FileChangedCallback(ChangedPath change)
             {
-                if (changeFilter(path, kind) is { } changedFile)
+                if (acceptChange(change))
                 {
-                    fileChangedSource.TrySetResult(changedFile);
+                    fileChangedSource.TrySetResult(change);
                 }
             }
 
-            ChangedFile? changedFile;
+            ChangedPath? change;
 
             OnFileChange += FileChangedCallback;
             try
             {
                 startedWatching?.Invoke();
-                changedFile = await fileChangedSource.Task;
+                change = await fileChangedSource.Task;
             }
             finally
             {
                 OnFileChange -= FileChangedCallback;
             }
 
-            return changedFile;
+            return change;
         }
 
         public static async ValueTask WaitForFileChangeAsync(string filePath, IReporter reporter, Action? startedWatching, CancellationToken cancellationToken)
@@ -146,7 +154,7 @@ public static async ValueTask WaitForFileChangeAsync(string filePath, IReporter
             watcher.WatchDirectories([Path.GetDirectoryName(filePath)!]);
 
             var fileChange = await watcher.WaitForFileChangeAsync(
-                changeFilter: (path, kind) => path == filePath ? new ChangedFile(new FileItem { FilePath = path, ContainingProjectPaths = [] }, kind) : null,
+                acceptChange: change => change.Path == filePath,
                 startedWatching,
                 cancellationToken);
 

src/BuiltInTools/dotnet-watch/Internal/FileWatcher.cs

@@ -10,4 +10,6 @@ internal enum ChangeKind
     Delete
 }
 
-internal readonly record struct ChangedFile(FileItem Item, ChangeKind Change);
+internal readonly record struct ChangedFile(FileItem Item, ChangeKind Kind);
+
+internal readonly record struct ChangedPath(string Path, ChangeKind Kind);

src/BuiltInTools/dotnet-watch/Internal/FileWatcher/ChangeKind.cs

@@ -7,7 +7,7 @@ namespace Microsoft.DotNet.Watch
 {
     internal sealed class EventBasedDirectoryWatcher : IDirectoryWatcher
     {
-        public event EventHandler<(string filePath, ChangeKind kind)>? OnFileChange;
+        public event EventHandler<ChangedPath>? OnFileChange;
 
         public event EventHandler<Exception>? OnError;
 
@@ -118,7 +118,7 @@ private void WatcherAddedHandler(object sender, FileSystemEventArgs e)
         private void NotifyChange(string fullPath, ChangeKind kind)
         {
             // Only report file changes
-            OnFileChange?.Invoke(this, (fullPath, kind));
+            OnFileChange?.Invoke(this, new ChangedPath(fullPath, kind));
         }
 
         private void CreateFileSystemWatcher()

src/BuiltInTools/dotnet-watch/Internal/FileWatcher/EventBasedDirectoryWatcher.cs

@@ -5,7 +5,7 @@ namespace Microsoft.DotNet.Watch
 {
     internal interface IDirectoryWatcher : IDisposable
     {
-        event EventHandler<(string filePath, ChangeKind kind)> OnFileChange;
+        event EventHandler<ChangedPath> OnFileChange;
 
         event EventHandler<Exception> OnError;
 

src/BuiltInTools/dotnet-watch/Internal/FileWatcher/IDirectoryWatcher.cs

@@ -21,7 +21,7 @@ internal sealed class PollingDirectoryWatcher : IDirectoryWatcher
 
         private volatile bool _disposed;
 
-        public event EventHandler<(string filePath, ChangeKind kind)>? OnFileChange;
+        public event EventHandler<ChangedPath>? OnFileChange;
 
 #pragma warning disable CS0067 // not used
         public event EventHandler<Exception>? OnError;
@@ -212,7 +212,7 @@ private void NotifyChanges()
                     break;
                 }
 
-                OnFileChange?.Invoke(this, (path, kind));
+                OnFileChange?.Invoke(this, new ChangedPath(path, kind));
             }
         }
 

src/BuiltInTools/dotnet-watch/Internal/FileWatcher/PollingDirectoryWatcher.cs

@@ -72,6 +72,10 @@ public bool TryGetMessage(string? prefix, object?[] args, [NotNullWhen(true)] ou
         public static readonly MessageDescriptor ApplyUpdate_FileContentDoesNotMatchBuiltSource = new("{0} Expected if a source file is updated that is linked to project whose build is not up-to-date.", "⌚", MessageSeverity.Verbose, s_id++);
         public static readonly MessageDescriptor ConfiguredToLaunchBrowser = new("dotnet-watch is configured to launch a browser on ASP.NET Core application startup.", "⌚", MessageSeverity.Verbose, s_id++);
         public static readonly MessageDescriptor ConfiguredToUseBrowserRefresh = new("Configuring the app to use browser-refresh middleware", "⌚", MessageSeverity.Verbose, s_id++);
+        public static readonly MessageDescriptor IgnoringChangeInHiddenDirectory = new("Ignoring change in hidden directory '{0}': {1} '{2}'", "⌚", MessageSeverity.Verbose, s_id++);
+        public static readonly MessageDescriptor IgnoringChangeInOutputDirectory = new("Ignoring change in output directory: {0} '{1}'", "⌚", MessageSeverity.Verbose, s_id++);
+        public static readonly MessageDescriptor FileAdditionTriggeredReEvaluation = new("File addition triggered re-evaluation.", "⌚", MessageSeverity.Verbose, s_id++);
+        public static readonly MessageDescriptor NoHotReloadChangesToApply = new ("No C# changes to apply.", "⌚", MessageSeverity.Output, s_id++);
     }
 
     internal interface IReporter