Watch directories moved into the tree and report their content

Automatic subtree watching only reacted to `CREATE`, so a directory
moved in from elsewhere stayed unwatched. It is now handled like a
created one. Items that already exist in such a directory never
produce kernel events; they are reported with the same event kind
and `synthesized` set to `true`, so consumers can treat them as
newly appeared.

Sources/Inotify/DirectoryResolver.swift

@@ -23,6 +23,19 @@ public struct DirectoryResolver {
 		return resolved
 	}
 
+	/// The direct children of `directory`, without the excluded names.
+	static func entries(of directory: FilePath, excluding itemNames: Set<String> = []) async throws -> [(name: String, isDirectory: Bool)] {
+		let directoryHandle = try await fileManager.openDirectory(atPath: directory)
+		var entries: [(name: String, isDirectory: Bool)] = []
+		for try await childContent in directoryHandle.listContents() {
+			guard let name = childContent.path.lastComponent?.string else { continue }
+			guard !itemNames.contains(name) else { continue }
+			entries.append((name: name, isDirectory: childContent.type == .directory))
+		}
+		try await directoryHandle.close()
+		return entries
+	}
+
 	private static func withSubdirectories(at path: FilePath, recursive: Bool = false, body: (FilePath) async throws -> Void) async throws {
 		let directoryHandle = try await fileManager.openDirectory(atPath: path)
 		for try await childContent in directoryHandle.listContents() {

Sources/Inotify/Inotify.docc/WatchingDirectoryTrees.md

@@ -31,7 +31,7 @@ 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.
+Internally this listens for `CREATE` and `MOVED_TO` events carrying the ``InotifyEventMask/isDir`` flag and installs new watches with the same mask on the subdirectory and its subtree whenever one appears. Items that already exist inside such a subdirectory are reported with ``InotifyEvent/synthesized`` set to `true`, since the kernel never produces events for them; a synthesized event may duplicate a kernel event for the same item.
 
 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.
 

Sources/Inotify/Inotify.swift

@@ -1,5 +1,6 @@
 import Dispatch
 import CInotify
+import SystemPackage
 
 public actor Inotify {
 	private let fd: CInt
@@ -7,6 +8,7 @@ public actor Inotify {
 	private var watches = InotifyWatchManager()
 	private nonisolated(unsafe) let eventReader: any DispatchSourceRead
 	private nonisolated let eventStream: AsyncStream<RawInotifyEvent>
+	private nonisolated let continuation: AsyncStream<RawInotifyEvent>.Continuation
 	public nonisolated var events: AsyncCompactMapSequence<AsyncStream<RawInotifyEvent>, InotifyEvent> {
 		self.eventStream.compactMap(self.transform(_:))
 	}
@@ -25,7 +27,7 @@ public actor Inotify {
 		guard self.fd >= 0 else {
 			throw InotifyError.initFailed(errno: cinotify_get_errno())
 		}
-		(self.eventReader, self.eventStream) = Self.createEventReader(
+		(self.eventReader, self.eventStream, self.continuation) = Self.createEventReader(
 			forFileDescriptor: fd,
 			bufferingPolicy: bufferingPolicy
 		)
@@ -126,20 +128,48 @@ public actor Inotify {
 	}
 
 	private func addWatchInCaseOfAutomaticSubtreeWatching(_ event: InotifyEvent) async {
-		guard watches.isAutomaticSubtreeWatching(event.watchDescriptor),
-			  event.mask.contains(.create),
-			  event.mask.contains(.isDir) else {
+		guard !event.synthesized,
+			  watches.isAutomaticSubtreeWatching(event.watchDescriptor),
+			  event.mask.contains(.isDir),
+			  let kind = Self.subtreeTrigger(in: event.mask) else {
 			return
 		}
 
 		guard let mask = self.watches.mask(forId: event.watchDescriptor) else { return }
-		let _ = try? await self.addWatchWithAutomaticSubtreeWatching(forDirectory: event.path.string, mask: mask)
+		guard let wds = try? await self.addWatchWithAutomaticSubtreeWatching(forDirectory: event.path.string, mask: mask) else { return }
+		await self.synthesizeEvents(forContentOfWatches: wds, kind: kind, cookie: event.cookie)
+	}
+
+	private static func subtreeTrigger(in mask: InotifyEventMask) -> InotifyEventMask? {
+		if mask.contains(.create) { return .create }
+		if mask.contains(.movedTo) { return .movedTo }
+		return nil
+	}
+
+	/// Items that already exist when a directory becomes watched never
+	/// produce kernel events, so they are reported as if they had just
+	/// appeared, marked as synthesized.
+	private func synthesizeEvents(forContentOfWatches wds: [CInt], kind: InotifyEventMask, cookie: UInt32) async {
+		for wd in wds {
+			guard let directory = self.watches.path(forId: wd) else { continue }
+			guard let entries = try? await DirectoryResolver.entries(of: FilePath(directory), excluding: self.excludedItemNames) else { continue }
+			for entry in entries {
+				let mask: InotifyEventMask = entry.isDirectory ? [kind, .isDir] : kind
+				self.continuation.yield(RawInotifyEvent(
+					watchDescriptor: wd,
+					mask: mask,
+					cookie: cookie,
+					name: entry.name,
+					synthesized: true
+				))
+			}
+		}
 	}
 
 	private static func createEventReader(
 		forFileDescriptor fd: CInt,
 		bufferingPolicy: AsyncStream<RawInotifyEvent>.Continuation.BufferingPolicy
-	) -> (any DispatchSourceRead, AsyncStream<RawInotifyEvent>) {
+	) -> (any DispatchSourceRead, AsyncStream<RawInotifyEvent>, AsyncStream<RawInotifyEvent>.Continuation) {
 		let (stream, continuation) = AsyncStream<RawInotifyEvent>.makeStream(
 			of: RawInotifyEvent.self,
 			bufferingPolicy: bufferingPolicy
@@ -161,6 +191,6 @@ public actor Inotify {
 		}
 		reader.activate()
 
-		return (reader, stream)
+		return (reader, stream, continuation)
 	}
 }

Sources/Inotify/InotifyEvent.swift

@@ -12,6 +12,9 @@ public struct InotifyEvent: Sendable, Hashable, CustomStringConvertible {
 	public let mask: InotifyEventMask
 	public let cookie: UInt32
 	public let path: FilePath
+	/// Whether the event was produced by the library for an item that already
+	/// existed when its directory became watched, rather than by the kernel.
+	public let synthesized: Bool
 
 	public var description: String {
 		var parts = ["InotifyEvent(wd: \(watchDescriptor), mask: \(mask), path: \"\(path)\""]
@@ -27,7 +30,8 @@ extension InotifyEvent {
 			watchDescriptor: rawEvent.watchDescriptor,
 			mask: rawEvent.mask,
 			cookie: rawEvent.cookie,
-			path: dirPath.appending(rawEvent.name)
+			path: dirPath.appending(rawEvent.name),
+			synthesized: rawEvent.synthesized
 		)
 	}
 }

Sources/Inotify/InotifyEventParser.swift

@@ -31,7 +31,8 @@ struct InotifyEventParser {
 				watchDescriptor: rawEvent.wd,
 				mask: InotifyEventMask(rawValue: rawEvent.mask),
 				cookie: rawEvent.cookie,
-				name: Self.extractName(from: eventPointer, nameLength: rawEvent.len)
+				name: Self.extractName(from: eventPointer, nameLength: rawEvent.len),
+				synthesized: false
 			))
 
 			offset += Self.eventSize(nameLength: rawEvent.len)

Sources/Inotify/RawInotifyEvent.swift

@@ -3,6 +3,9 @@ public struct RawInotifyEvent: Sendable, Hashable, CustomStringConvertible {
 	public let mask: InotifyEventMask
 	public let cookie: UInt32
 	public let name: String
+	/// Whether the event was produced by the library for an item that already
+	/// existed when its directory became watched, rather than by the kernel.
+	public let synthesized: Bool
 
 	public var description: String {
 		var parts = ["RawInotifyEvent(wd: \(watchDescriptor), mask: \(mask), name: \"\(name)\""]