Add missing bits and bobs to IFileSystem

src/HotAvalonia/IO/CachingFileSystem.cs

@@ -51,6 +51,10 @@ public CachingFileSystem(IFileSystem fileSystem, IEqualityComparer<string>? file
     public IFileSystemWatcher CreateFileSystemWatcher()
         => _fileSystem.CreateFileSystemWatcher();
 
+    /// <inheritdoc/>
+    public ValueTask<IFileSystemWatcher> CreateFileSystemWatcherAsync(CancellationToken cancellationToken = default)
+        => _fileSystem.CreateFileSystemWatcherAsync(cancellationToken);
+
     /// <inheritdoc/>
     public bool DirectoryExists([NotNullWhen(true)] string? path)
         => _fileSystem.DirectoryExists(path);
@@ -93,11 +97,12 @@ public string GetFullPath(string path)
         => _fileSystem.GetFullPath(path);
 
     /// <inheritdoc/>
-    public string GetDirectoryName(string path)
+    public string? GetDirectoryName(string? path)
         => _fileSystem.GetDirectoryName(path);
 
     /// <inheritdoc/>
-    public string GetFileName(string path)
+    [return: NotNullIfNotNull(nameof(path))]
+    public string? GetFileName(string? path)
         => _fileSystem.GetFileName(path);
 
     /// <inheritdoc/>
@@ -138,6 +143,14 @@ public async Task<Stream> OpenReadAsync(string path, CancellationToken cancellat
         return await _cache.GetOrAdd(path, x => new(x, _fileSystem)).OpenReadAsync(cancellationToken).ConfigureAwait(false);
     }
 
+    /// <inheritdoc/>
+    public void Dispose()
+        => _fileSystem.Dispose();
+
+    /// <inheritdoc/>
+    public ValueTask DisposeAsync()
+        => _fileSystem.DisposeAsync();
+
     /// <summary>
     /// Represents a cached file entry.
     /// </summary>

src/HotAvalonia/IO/FileObserver.cs

@@ -267,10 +267,10 @@ private void Watch(string fileName)
 
         lock (_lock)
         {
-            string newPath = string.IsNullOrEmpty(_watcher.Path)
+            string? newPath = string.IsNullOrEmpty(_watcher.Path)
                 ? FileSystem.GetDirectoryName(fileName)
                 : FileSystem.GetCommonPath(fileName, _watcher.Path);
-            if (string.IsNullOrEmpty(newPath))
+            if (newPath is null or { Length: 0 })
                 return;
 
             _watcher.Path = newPath;

src/HotAvalonia/IO/IFileSystem.cs

@@ -5,7 +5,7 @@ namespace HotAvalonia.IO;
 /// <summary>
 /// Represents an abstraction for interacting with a file system.
 /// </summary>
-public interface IFileSystem
+public interface IFileSystem : IDisposable, IAsyncDisposable
 {
     /// <summary>
     /// Gets the <see cref="StringComparer"/> used to compare file or directory paths.
@@ -42,6 +42,15 @@ public interface IFileSystem
     /// </returns>
     IFileSystemWatcher CreateFileSystemWatcher();
 
+    /// <summary>
+    /// Asynchronously creates a new instance of <see cref="IFileSystemWatcher"/> to monitor changes in the file system.
+    /// </summary>
+    /// <param name="cancellationToken">The token to monitor for cancellation requests.</param>
+    /// <returns>
+    /// A new <see cref="IFileSystemWatcher"/> instance.
+    /// </returns>
+    ValueTask<IFileSystemWatcher> CreateFileSystemWatcherAsync(CancellationToken cancellationToken = default);
+
     /// <summary>
     /// Returns the absolute path for the specified path string.
     /// </summary>
@@ -58,7 +67,7 @@ public interface IFileSystem
     /// <returns>
     /// The directory information for <paramref name="path"/>.
     /// </returns>
-    string GetDirectoryName(string path);
+    string? GetDirectoryName(string? path);
 
     /// <summary>
     /// Returns the file name and extension of the specified path string.
@@ -67,7 +76,8 @@ public interface IFileSystem
     /// <returns>
     /// The characters after the last directory separator character in <paramref name="path"/>.
     /// </returns>
-    string GetFileName(string path);
+    [return: NotNullIfNotNull(nameof(path))]
+    string? GetFileName(string? path);
 
     /// <summary>
     /// Changes the extension of a path string.

src/HotAvalonia/IO/LocalFileSystem.cs

@@ -1,5 +1,6 @@
 #pragma warning disable RS0030 // Do not use banned APIs
 
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 
@@ -34,6 +35,9 @@ internal sealed class LocalFileSystem : IFileSystem
     /// <inheritdoc/>
     public IFileSystemWatcher CreateFileSystemWatcher() => new LocalFileSystemWatcher(this);
 
+    /// <inheritdoc/>
+    ValueTask<IFileSystemWatcher> IFileSystem.CreateFileSystemWatcherAsync(CancellationToken cancellationToken) => new(CreateFileSystemWatcher());
+
     /// <inheritdoc/>
     public DateTime GetLastWriteTimeUtc(string path) => File.GetLastWriteTimeUtc(path);
 
@@ -44,10 +48,11 @@ internal sealed class LocalFileSystem : IFileSystem
     public string GetFullPath(string path) => Path.GetFullPath(path);
 
     /// <inheritdoc/>
-    public string GetDirectoryName(string path) => Path.GetDirectoryName(path);
+    public string? GetDirectoryName(string? path) => Path.GetDirectoryName(path);
 
     /// <inheritdoc/>
-    public string GetFileName(string path) => Path.GetFileName(path);
+    [return: NotNullIfNotNull(nameof(path))]
+    public string? GetFileName(string? path) => Path.GetFileName(path);
 
     /// <inheritdoc/>
     public string Combine(string path1, string path2) => Path.Combine(path1, path2);
@@ -83,6 +88,12 @@ async IAsyncEnumerable<string> IFileSystem.EnumerateFilesAsync(string path, stri
 
     /// <inheritdoc/>
     Task<Stream> IFileSystem.OpenReadAsync(string path, CancellationToken cancellationToken) => Task.FromResult(OpenRead(path));
+
+    /// <inheritdoc/>
+    void IDisposable.Dispose() { }
+
+    /// <inheritdoc/>
+    ValueTask IAsyncDisposable.DisposeAsync() => default;
 }
 
 /// <summary>