Add integration tests for inofity limits

inotify exposes a /proc interface to limit kernel memory usage. If those
limits are set too low, inotify cannot add all watches. The integration
test verifies, that Inotify yields an error in that case.

Package.swift

@@ -36,7 +36,10 @@ let package = Package(
 		),
 		.testTarget(
 			name: "InotifyIntegrationTests",
-			dependencies: ["Inotify"],
+			dependencies: [
+				"Inotify",
+				.product(name: "SystemPackage", package: "swift-system")
+			],
 		),
 		.executableTarget(
 			name: "TaskCLI",

Sources/TaskCLI/Test Command.swift

@@ -24,7 +24,7 @@ struct TestCommand: AsyncParsableCommand {
 		logger.debug("Current directory", metadata: ["current-directory": "\(currentDirectory)"])
 		async let monitorResult = Subprocess.run(
 			.name("docker"),
-			arguments: ["run", "-v", "\(currentDirectory):/code", "--platform", "linux/arm64", "-w", "/code", "swift:latest", "swift", "test"],
+			arguments: ["run", "-v", "\(currentDirectory):/code", "--security-opt", "systempaths=unconfined", "--platform", "linux/arm64", "-w", "/code", "swift:latest", "/bin/bash", "-c", "swift test --skip InotifyLimitTests; swift test --skip-build --filter InotifyLimitTests"],
 			preferredBufferSize: 10,
 		) { execution, standardInput, standardOutput, standardError in
 			print("")

Tests/InotifyIntegrationTests/InotifyLimitTests.swift

@@ -0,0 +1,43 @@
+import Testing
+import Foundation
+@testable import Inotify
+
+@Suite("Inotify Limits", .serialized)
+struct InotifyLimitTests {
+	@Test func throwsIfInotifyUpperLimitReached() async throws {
+		try await withTempDir { dir in
+			try await withInotifyWatchLimit(of: 10) {
+				try createSubdirectorytree(at: dir, foldersPerLevel: 4, levels: 3)
+				try await Task.sleep(for: .milliseconds(100))
+
+				await #expect(throws: InotifyError.self) {
+					let watcher = try Inotify()
+					try await watcher.addRecursiveWatch(forDirectory: dir, mask: .allEvents)
+				}
+			}
+		}
+	}
+
+	@Test func watchesMassivSubtreesIfAllowed() async throws {
+		try await withTempDir { dir in
+			try await withInotifyWatchLimit(of: 1000) {
+				try createSubdirectorytree(at: dir, foldersPerLevel: 8, levels: 3)
+				let subDirectory = "\(dir)/Folder 8/Folder 8/Folder 8"
+				let filepath = "\(subDirectory)/new-file.txt"
+				try await Task.sleep(for: .milliseconds(100))
+
+				let events = try await getEventsForTrigger(
+					in: dir,
+					mask: [.create],
+					recursive: .recursive
+				) { _ in
+					assert(FileManager.default.fileExists(atPath: subDirectory))
+					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/createSubdirectorytree.swift

@@ -0,0 +1,53 @@
+import Foundation
+import SystemPackage
+
+func createSubdirectorytree(at dir: String, foldersPerLevel: Int, levels: Int) throws {
+	let fileManager = FileManager.default
+
+	for path in SubfolderTreeIterator(basePath: dir, foldersPerLevel: foldersPerLevel, levels: levels) {
+		try fileManager.createDirectory(
+			at: path,
+			withIntermediateDirectories: true,
+			attributes: nil
+		)
+	}
+}
+
+struct SubfolderTreeIterator: IteratorProtocol, Sequence {
+	let basePath: URL
+	let foldersPerLevel: Int
+	let levels: Int
+	private var indices: [Int]
+	private var done = false
+
+	init(basePath: String, foldersPerLevel: Int, levels: Int) {
+		self.basePath = URL(filePath: basePath)
+		self.foldersPerLevel = foldersPerLevel
+		self.levels = levels
+		self.indices = Array(repeating: 1, count: levels)
+	}
+
+	mutating func next() -> URL? {
+		guard !done else { return nil }
+
+		let path = indices.reduce(basePath) { partialPath, index in
+			partialPath.appending(path: "Folder \(index)")
+		}
+
+		// Advance indices (odometer-style, rightmost increments first)
+		var carry = true
+		for i in (0..<levels).reversed() {
+			if carry {
+				indices[i] += 1
+				if indices[i] > foldersPerLevel {
+					indices[i] = 1
+				} else {
+					carry = false
+				}
+			}
+		}
+		if carry { done = true }
+
+		return path
+	}
+}

Tests/InotifyIntegrationTests/Utilities/withLowInotifyWatchLimit.swift

@@ -0,0 +1,22 @@
+import Foundation
+
+func withInotifyWatchLimit(of limit: Int, _ body: () async throws -> Void) async throws {
+	let confPath = URL(filePath: "/proc/sys/fs/inotify")
+	let filenames = ["max_user_watches", "max_user_instances", "max_queued_events"]
+	var previousLimits: [String: String] = [:]
+
+	for filename in filenames {
+		let filePath = confPath.appending(path: filename)
+		let currentLimit = try String(contentsOf: filePath, encoding: .utf8)
+		previousLimits[filename] = currentLimit
+		try "\(limit)".write(to: filePath, atomically: false, encoding: .utf8)
+	}
+
+	try await body()
+
+	for filename in filenames {
+		let filePath = confPath.appending(path: filename)
+		guard let previousLimit = previousLimits[filename] else { continue }
+		try previousLimit.write(to: filePath, atomically: false, encoding: .utf8)
+	}
+}