Forward localized descriptions of extension errors to host (#36)

TophatKit/Sources/TophatKit/ArtifactProvider.swift

@@ -35,6 +35,9 @@ public protocol ArtifactProvider {
 	///
 	/// Throw any errors if they ocurred. Use any parameters wrapped with ``Parameter`` to
 	/// collect inputs from Tophat to implement the retrieval mechanism.
+	///
+	/// To display an error message in the user interface, conform thrown errors to the
+	/// `LocalizedError` protocol.
 	/// - Returns: A ``ArtifactProviderResult`` containing the output.
 	func retrieve() async throws -> Result
 

TophatKit/Sources/TophatKit/Internal/XPC/ExtensionXPCGenericLocalizedError.swift

@@ -0,0 +1,28 @@
+//
+//  ExtensionXPCGenericLocalizedError.swift
+//  TophatKit
+//
+//  Created by Lukas Romsicki on 2024-11-27.
+//
+
+import Foundation
+
+struct ExtensionXPCGenericLocalizedError: LocalizedError {
+	let errorDescription: String?
+	let failureReason: String?
+	let recoverySuggestion: String?
+	let helpAnchor: String?
+
+	init?(nsError: NSError) {
+		let userInfo = nsError.userInfo
+
+		self.errorDescription = userInfo["errorDescription"] as? String
+		self.failureReason = userInfo["failureReason"] as? String
+		self.recoverySuggestion = userInfo["recoverySuggestion"] as? String
+		self.helpAnchor = userInfo["helpAnchor"] as? String
+
+		guard errorDescription != nil || failureReason != nil || recoverySuggestion != nil || helpAnchor != nil else {
+			return nil
+		}
+	}
+}

TophatKit/Sources/TophatKit/Internal/XPC/ExtensionXPCReceivedMessage.swift

@@ -39,7 +39,8 @@ struct ExtensionXPCReceivedMessageContainer {
 					replyHandler(nil, error)
 				}
 			case .failure(let error):
-				replyHandler(nil, error)
+				// The error will be an NSError over XPC anyway.
+				replyHandler(nil, NSError(embeddingLocalizedDescriptionsFrom: error))
 		}
 	}
 }

TophatKit/Sources/TophatKit/Internal/XPC/ExtensionXPCSession.swift

@@ -82,7 +82,10 @@ extension ExtensionXPCSession {
 			}
 
 			service.send(identifier: message.identifier, data: dataToSend) { dataFromReply, error in
-				if let error {
+				if let nsError = error as? NSError, let localizedError = ExtensionXPCGenericLocalizedError(nsError: nsError) {
+					continuation.resume(throwing: localizedError)
+					return
+				} else if let error {
 					continuation.resume(throwing: error)
 					return
 				}

TophatKit/Sources/TophatKit/Internal/XPC/NSError+Extensions.swift

@@ -0,0 +1,24 @@
+//
+//  NSError+Extensions.swift
+//  TophatKit
+//
+//  Created by Lukas Romsicki on 2024-11-27.
+//
+
+import Foundation
+
+extension NSError {
+	convenience init(embeddingLocalizedDescriptionsFrom error: Error) {
+		let nsError = error as NSError
+		var newUserInfo = nsError.userInfo
+
+		if let localizedError = error as? LocalizedError {
+			newUserInfo["errorDescription"] = localizedError.errorDescription
+			newUserInfo["failureReason"] = localizedError.failureReason
+			newUserInfo["recoverySuggestion"] = localizedError.recoverySuggestion
+			newUserInfo["helpAnchor"] = localizedError.helpAnchor
+		}
+
+		self.init(domain: nsError.domain, code: nsError.code, userInfo: newUserInfo)
+	}
+}