Add a quirks mode switch for issue dotnet/aspnetcore#2808

Author: Nate McMaster

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

@@ -33,6 +33,14 @@ public class PhysicalFilesWatcher : IDisposable
         private readonly string _root;
         private readonly bool _pollForChanges;
 
+        /// <summary>
+        /// If for some unforseen reason the patch for aspnet/Home#2808 causes issues for users,
+        /// this gives them a way to disable the behavior change.
+        /// They is enabled by setting <c>Switch.Microsoft.AspNetCore.FileProviders.IgnoreEmptyRenameEvents</c> to <c>true</c>
+        /// in the app configuration.
+        /// </summary>
+        private readonly bool _emptyRenameEventQuirksMode;
+
         /// <summary>
         /// Initializes an instance of <see cref="PhysicalFilesWatcher" /> that watches files in <paramref name="root" />.
         /// Wraps an instance of <see cref="System.IO.FileSystemWatcher" />
@@ -48,6 +56,7 @@ public PhysicalFilesWatcher(
             FileSystemWatcher fileSystemWatcher,
             bool pollForChanges)
         {
+            AppContext.TryGetSwitch("Switch.Microsoft.AspNetCore.FileProviders.IgnoreEmptyRenameEvents", out _emptyRenameEventQuirksMode);
             _root = root;
             _fileWatcher = fileSystemWatcher;
             _fileWatcher.IncludeSubdirectories = true;
@@ -245,7 +254,7 @@ ex is SecurityException ||
 
         private void ReportChangeForMatchedEntries(string path)
         {
-            if (string.IsNullOrEmpty(path))
+            if (!_emptyRenameEventQuirksMode && string.IsNullOrEmpty(path))
             {
                 // System.IO.FileSystemWatcher may trigger events that are missing the file name,
                 // which makes it appear as if the root directory is renamed or deleted. Moving the root directory
@@ -361,4 +370,4 @@ public ChangeTokenInfo(
             public Matcher Matcher { get; }
         }
     }
-}
+}

test/Microsoft.Extensions.FileProviders.Physical.Tests/PhysicalFilesWatcherTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.IO;
 using System.Threading.Tasks;
 using Xunit;
@@ -32,6 +33,19 @@ public void CreateFileChangeToken_DoesNotAllowPathsAboveRoot()
         [Fact]
         public async Task HandlesOnRenamedEventsThatMatchRootPath()
         {
+            AppContext.SetSwitch("Switch.Microsoft.AspNetCore.FileProviders.IgnoreEmptyRenameEvents", true);
+            using (var root = new DisposableFileSystem())
+            using (var fileSystemWatcher = new MockFileSystemWatcher(root.RootPath))
+            using (var physicalFilesWatcher = new PhysicalFilesWatcher(root.RootPath + Path.DirectorySeparatorChar, fileSystemWatcher, pollForChanges: false))
+            {
+                var token = physicalFilesWatcher.CreateFileChangeToken("**");
+                token.RegisterChangeCallback(o => { }, null);
+
+                Assert.Throws<ArgumentException>(
+                    () => fileSystemWatcher.CallOnRenamed(new RenamedEventArgs(WatcherChangeTypes.Renamed, root.RootPath, string.Empty, string.Empty)));
+            }
+
+            AppContext.SetSwitch("Switch.Microsoft.AspNetCore.FileProviders.IgnoreEmptyRenameEvents", false);
             using (var root = new DisposableFileSystem())
             using (var fileSystemWatcher = new MockFileSystemWatcher(root.RootPath))
             using (var physicalFilesWatcher = new PhysicalFilesWatcher(root.RootPath + Path.DirectorySeparatorChar, fileSystemWatcher, pollForChanges: false))