Implement auto subtree watching of a directory

Allow recursively watching a directory while adding newly created
subdirectories to the inotify watch list.

Tests/InotifyIntegrationTests/RecursiveEventTests.swift

@@ -13,11 +13,31 @@ struct RecursiveEventTests {
 			let events = try await getEventsForTrigger(
 				in: dir,
 				mask: [.create],
-				recursive: true
+				recursive: .recursive
 			) { _ in try createFile(at: "\(filepath)", contents: "hello") }
 
 			let createEvent = events.first { $0.mask.contains(.create) && $0.path.string == filepath }
 			#expect(createEvent != nil, "Expected CREATE for '\(filepath)', got: \(events)")
 		}
 	}
+
+	@Test func newSubfoldersOfRecursiveWatchAreAutomaticallyWatchedToo() async throws {
+		try await withTempDir { dir in
+			let subDirectory = "\(dir)/Subfolder"
+			let filepath = "\(subDirectory)/modify-target.txt"
+
+			let events = try await getEventsForTrigger(
+				in: dir,
+				mask: [.create],
+				recursive: .withAutomaticSubtreeWatching
+			) { _ in
+				try FileManager.default.createDirectory(atPath: subDirectory, withIntermediateDirectories: true)
+				try await Task.sleep(for: .milliseconds(200))
+				try createFile(at: "\(filepath)", contents: "hello")
+			}
+
+			let createEvent = events.first { $0.mask.contains(.create) && $0.path.string == filepath }
+			#expect(createEvent != nil, "Expected CREATE for '\(filepath)', got: \(events)")
+		}
+	}
 }

Tests/InotifyIntegrationTests/Utilities/getEventsForTrigger.swift

@@ -1,16 +1,25 @@
 import Inotify
 
+enum RecursivKind {
+	case nonrecursive
+	case recursive
+	case withAutomaticSubtreeWatching
+}
+
 func getEventsForTrigger(
 	in dir: String,
 	mask: InotifyEventMask,
-	recursive: Bool = false,
+	recursive: RecursivKind = .nonrecursive,
 	trigger: @escaping (String) async throws -> Void,
 ) async throws -> [InotifyEvent] {
 	let watcher = try Inotify()
-	if recursive {
-		try await watcher.addRecursiveWatch(forDirectory: dir, mask: mask)
-	} else {
+	switch recursive {
+	case .nonrecursive:
 		try await watcher.addWatch(path: dir, mask: mask)
+	case .recursive:
+		try await watcher.addRecursiveWatch(forDirectory: dir, mask: mask)
+	case .withAutomaticSubtreeWatching:
+		try await watcher.addWatchWithAutomaticSubtreeWatching(forDirectory: dir, mask: mask)
 	}
 
 	let eventTask = Task {