fix: skip a file the hashing pass cannot read instead of aborting [patch]

.gitignore

@@ -203,6 +203,11 @@ PublishScripts/
 **/[Pp]ackages/*
 # except build/, which is used as an MSBuild target.
 !**/[Pp]ackages/build/
+# and except a Unity project's Packages/, which is source: Unity's package manifest and its
+# resolved lock file are both meant to be committed, and a NuGet restore folder never contains
+# a file by either name.
+!**/[Pp]ackages/manifest.json
+!**/[Pp]ackages/packages-lock.json
 # Uncomment if necessary however generally it will be regenerated when needed
 #!**/[Pp]ackages/repositories.config
 # NuGet v3's project.json files produces more ignorable files
@@ -651,3 +656,16 @@ Temporary Items
 
 # ImGui.ini files
 imgui.ini
+
+# Game engine projects
+#
+# Godot: the import cache, and the mono/temp bin+obj a C# build writes.
+.godot/
+
+# Unity: .meta files are source, not the Visual Studio C++ build artifact that the `*.meta` rule
+# further up targets. Unity generates one per asset and it carries the GUID that scenes, prefabs
+# and serialized references point at, so ignoring them gives every clone fresh GUIDs and silently
+# breaks those references - including for a plug-in whose .dll is itself a build output. This
+# negation has to come after that rule to win, and is scoped to the asset tree so the Visual
+# Studio artifact stays ignored everywhere else.
+!**/[Aa]ssets/**/*.meta

FileDeduplicator.Test/FileScannerAndHasherTests.cs

@@ -164,4 +164,36 @@ public void ParallelHashingAgreesWithSingleFileHashing()
 			Assert.AreEqual(FileHasher.ComputeHash(file), hashes[file]);
 		}
 	}
+
+	/// <summary>
+	/// One file the process cannot read must not take the whole hashing pass down with it. Hashing
+	/// runs under <c>Parallel.ForEach</c>, so an exception escaping the delegate surfaces as an
+	/// <see cref="AggregateException"/> and discards the results every other thread had already
+	/// produced.
+	/// </summary>
+	[TestMethod]
+	public void HashingSkipsAnUnreadableFileAndStillHashesTheRest()
+	{
+		// Arrange
+		using TempTree tree = new();
+		AbsoluteFilePath readable = tree.Write("readable.txt", "one");
+		AbsoluteFilePath alsoReadable = tree.Write("also-readable.txt", "two");
+
+		// A directory standing in for a file: File.OpenRead throws UnauthorizedAccessException for
+		// one on every platform and for every user. Denying permission on a real file would not --
+		// a privileged process, root or an elevated CI runner, reads it anyway -- so that
+		// arrangement would pass whether or not the exception is handled.
+		string deniedPath = Path.Combine(tree.Root.WeakString, "denied");
+		_ = Directory.CreateDirectory(deniedPath);
+		AbsoluteFilePath unreadable = deniedPath.As<AbsoluteFilePath>();
+
+		// Act
+		Dictionary<AbsoluteFilePath, string> hashes = FileHasher.HashFiles([readable, alsoReadable, unreadable]);
+
+		// Assert
+		Assert.HasCount(2, hashes);
+		Assert.AreEqual(FileHasher.ComputeHash(readable), hashes[readable]);
+		Assert.AreEqual(FileHasher.ComputeHash(alsoReadable), hashes[alsoReadable]);
+		Assert.IsFalse(hashes.ContainsKey(unreadable));
+	}
 }

FileDeduplicator/FileHasher.cs

@@ -32,16 +32,29 @@ internal static Dictionary<AbsoluteFilePath, string> HashFiles(IReadOnlyList<Abs
 			}
 			catch (IOException ex)
 			{
-				lock (ConsoleLock)
-				{
-					Console.WriteLine($"  Error hashing {filePath.FileName}: {ex.Message}");
-				}
+				ReportSkipped(filePath, ex);
+			}
+			catch (UnauthorizedAccessException ex)
+			{
+				// Not an IOException, despite reading as one: a file the process is denied access to
+				// would otherwise escape this delegate, and Parallel.ForEach would surface it as an
+				// AggregateException that discards every hash the other threads had produced. This
+				// matches Deduplicator.StillMatchesGroup, which catches both for the same read.
+				ReportSkipped(filePath, ex);
 			}
 		});
 
 		return new Dictionary<AbsoluteFilePath, string>(results);
 	}
 
+	private static void ReportSkipped(AbsoluteFilePath filePath, Exception ex)
+	{
+		lock (ConsoleLock)
+		{
+			Console.WriteLine($"  Error hashing {filePath.FileName}: {ex.Message}");
+		}
+	}
+
 	internal static string ComputeHash(AbsoluteFilePath filePath)
 	{
 		using FileStream stream = File.OpenRead(filePath.WeakString);