Drop watches of directories that leave the tree

A directory moved out of a watched tree kept its kernel watches, so
later changes inside it were reported under the old path. Its
watches and those of its subdirectories are now removed on
`MOVED_FROM`. Watches the kernel reports as `IGNORED` are forgotten
as well, so a reused descriptor number cannot map to a stale path.

README.md

@@ -75,6 +75,8 @@ try await inotify.addWatchWithAutomaticSubtreeWatching(
 
 This is the most convenient option when you need full coverage of a growing directory tree.
 
+When a watched directory is moved out of the tree, the watches on it and on its subdirectories are removed, so no events are reported under the stale path.
+
 ## Excluding Items
 
 You can tell the `Inotify` actor to ignore certain file or directory names. Excluded names are skipped during recursive directory resolution (so no watch is installed on them) and silently dropped from the event stream:

Sources/Inotify/Inotify.docc/WatchingDirectoryTrees.md

@@ -33,6 +33,8 @@ let descriptors = try await inotify.addWatchWithAutomaticSubtreeWatching(
 
 Internally this listens for `CREATE` events carrying the ``InotifyEventMask/isDir`` flag and installs a new watch with the same mask whenever a subdirectory appears.
 
+When a directory is moved out of the watched tree, the watches on it and on its subdirectories are removed, so no events are reported under the stale path.
+
 ### Excluding Directories
 
 When watching large trees you often want to skip certain subdirectories entirely — version-control metadata, build artefacts, dependency caches, and so on. Call ``Inotify/Inotify/exclude(names:)`` **before** adding a recursive or automatic-subtree watch:

Sources/Inotify/Inotify.swift

@@ -99,8 +99,30 @@ public actor Inotify {
 		guard let path = self.watches.path(forId: rawEvent.watchDescriptor) else { return nil }
 		guard !self.excludedItemNames.contains(rawEvent.name) else { return nil }
 		let event = InotifyEvent.init(from: rawEvent, inDirectory: path)
+		self.forgetWatchInCaseTheKernelRemovedIt(event)
+		self.removeWatchesInCaseADirectoryLeftTheTree(event)
 		await self.addWatchInCaseOfAutomaticSubtreeWatching(event)
-		return InotifyEvent.init(from: rawEvent, inDirectory: path)
+		return event
+	}
+
+	/// The kernel reports `IN_IGNORED` once a watch is gone, whether it was
+	/// removed explicitly or because its item was deleted or unmounted.
+	/// Forgetting it keeps a reused descriptor number from mapping to a
+	/// stale path.
+	private func forgetWatchInCaseTheKernelRemovedIt(_ event: InotifyEvent) {
+		guard event.mask.contains(.ignored) else { return }
+		self.watches.remove(forId: event.watchDescriptor)
+	}
+
+	/// A directory moved out of a watched tree keeps its kernel watches,
+	/// which would then report events under the old path. Those watches
+	/// are removed instead.
+	private func removeWatchesInCaseADirectoryLeftTheTree(_ event: InotifyEvent) {
+		guard event.mask.contains(.movedFrom), event.mask.contains(.isDir) else { return }
+		for wd in self.watches.descriptors(under: event.path.string) {
+			inotify_rm_watch(self.fd, wd)
+			self.watches.remove(forId: wd)
+		}
 	}
 
 	private func addWatchInCaseOfAutomaticSubtreeWatching(_ event: InotifyEvent) async {

Sources/Inotify/InotifyWatchManager.swift

@@ -36,6 +36,14 @@ struct InotifyWatchManager {
 		return self.watchPaths[watchDescriptor]
 	}
 
+	/// The descriptors of the watch on `path` itself and of every watch below it.
+	func descriptors(under path: String) -> [CInt] {
+		let prefix = path.hasSuffix("/") ? path : path + "/"
+		return self.watchPaths
+			.filter { $0.value == path || $0.value.hasPrefix(prefix) }
+			.map(\.key)
+	}
+
 	func mask(forId watchDescriptor: CInt) -> InotifyEventMask? {
 		return self.watchMasks[watchDescriptor]
 	}

Tests/InotifyIntegrationTests/RecursiveEventTests.swift

@@ -58,4 +58,29 @@ struct RecursiveEventTests {
 			#expect(createEvent != nil, "Expected CREATE for '\(filepath)', got: \(events)")
 		}
 	}
+
+	@Test func stopsReportingForDirectoriesMovedOutOfTheWatchedTree() async throws {
+		try await withTempDir { dir in
+			let root = "\(dir)/Root"
+			let outside = "\(dir)/Outside"
+			let movedSource = "\(root)/Moved"
+			let movedDestination = "\(outside)/Moved"
+			let filename = "created-after-move.txt"
+			try FileManager.default.createDirectory(atPath: movedSource, withIntermediateDirectories: true)
+			try FileManager.default.createDirectory(atPath: outside, withIntermediateDirectories: true)
+
+			let events = try await getEventsForTrigger(
+				in: root,
+				mask: [.create, .movedFrom],
+				recursive: .withAutomaticSubtreeWatching
+			) { _ in
+				try FileManager.default.moveItem(atPath: movedSource, toPath: movedDestination)
+				try await Task.sleep(for: .milliseconds(400))
+				try createFile(at: "\(movedDestination)/\(filename)", contents: "hello")
+			}
+
+			let staleEvent = events.first { $0.mask.contains(.create) && $0.path.lastComponent?.string == filename }
+			#expect(staleEvent == nil, "Did not expect CREATE for '\(filename)' after its directory left the tree, got: \(events)")
+		}
+	}
 }