[Shared] Includes CodingPath in Source errors’ debug description (if available)

AltStore/Operations/FetchSourceOperation.swift

@@ -122,7 +122,35 @@ final class FetchSourceOperation: ResultOperation<Source>
                     decoder.managedObjectContext = childContext
                     decoder.sourceURL = self.sourceURL
                     
-                    let source = try decoder.decode(Source.self, from: data)
+                    let source: Source
+                    
+                    do
+                    {
+                        source = try decoder.decode(Source.self, from: data)
+                    }
+                    catch let error as DecodingError
+                    {
+                        let nsError = error as NSError
+                        guard let codingPath = nsError.userInfo[ALTNSCodingPathKey] as? [CodingKey] else { throw error }
+                        
+                        let rawComponents = codingPath.map { $0.intValue?.description ?? $0.stringValue }
+                        let pathDescription = rawComponents.joined(separator: " > ")
+                        
+                        var userInfo = nsError.userInfo
+                        
+                        if let debugDescription = nsError.localizedDebugDescription
+                        {
+                            let detailedDescription = debugDescription + "\n\n" + pathDescription
+                            userInfo[NSDebugDescriptionErrorKey] = detailedDescription
+                        }
+                        else
+                        {
+                            userInfo[NSDebugDescriptionErrorKey] = pathDescription
+                        }
+                        
+                        throw NSError(domain: nsError.domain, code: nsError.code, userInfo: userInfo)
+                    }
+                    
                     let identifier = source.identifier
                     
                     try self.verify(source, response: response)

Shared/Categories/NSError+ALTServerError.h

@@ -19,6 +19,8 @@ extern NSErrorUserInfoKey const ALTDeviceNameErrorKey;
 extern NSErrorUserInfoKey const ALTOperatingSystemNameErrorKey;
 extern NSErrorUserInfoKey const ALTOperatingSystemVersionErrorKey;
 
+extern NSErrorUserInfoKey const ALTNSCodingPathKey;
+
 typedef NS_ERROR_ENUM(AltServerErrorDomain, ALTServerError)
 {
     ALTServerErrorUnderlyingError = -1,

Shared/Categories/NSError+ALTServerError.m

@@ -37,6 +37,8 @@ NSErrorUserInfoKey const ALTDeviceNameErrorKey = @"deviceName";
 NSErrorUserInfoKey const ALTOperatingSystemNameErrorKey = @"ALTOperatingSystemName";
 NSErrorUserInfoKey const ALTOperatingSystemVersionErrorKey = @"ALTOperatingSystemVersion";
 
+NSErrorUserInfoKey const ALTNSCodingPathKey = @"NSCodingPath";
+
 @implementation NSError (ALTServerError)
 
 + (void)load