Replaces StoreApp.setVersions() preconditionFailure with runtime error

It’s more common than expected for apps to not have any app versions, so better to fail gracefully than crash.

AltStore/Browse/BrowseViewController.swift

@@ -193,8 +193,13 @@ private extension BrowseViewController
                     throw error
                 }
             }
-            catch
+            catch var error as NSError
             {
+                if error.localizedTitle == nil
+                {
+                    error = error.withLocalizedTitle(NSLocalizedString("Unable to Refresh Store", comment: ""))
+                }
+                                
                 DispatchQueue.main.async {
                     if self.dataSource.itemCount > 0
                     {

AltStore/News/NewsViewController.swift

@@ -210,8 +210,13 @@ private extension NewsViewController
                     throw error
                 }
             }
-            catch
+            catch var error as NSError
             {
+                if error.localizedTitle == nil
+                {
+                    error = error.withLocalizedTitle(NSLocalizedString("Unable to Refresh Store", comment: ""))
+                }
+                
                 DispatchQueue.main.async {
                     if self.dataSource.itemCount > 0
                     {

AltStoreCore/Model/MergePolicy.swift

@@ -10,6 +10,60 @@ import CoreData
 
 import Roxas
 
+extension MergeError
+{
+    enum Code: Int, ALTErrorCode
+    {
+        typealias Error = MergeError
+        
+        case noVersions
+    }
+    
+    static func noVersions(for app: AppProtocol) -> MergeError { .init(code: .noVersions, appName: app.name, appBundleID: app.bundleIdentifier) }
+}
+
+struct MergeError: ALTLocalizedError
+{
+    static var errorDomain: String { "AltStore.MergeError" }
+    
+    let code: Code
+    var errorTitle: String?
+    var errorFailure: String?
+    
+    var appName: String?
+    var appBundleID: String?
+    
+    var errorFailureReason: String {
+        switch self.code
+        {
+        case .noVersions:
+            var appName = NSLocalizedString("At least one app", comment: "")
+            if let name = self.appName, let bundleID = self.appBundleID
+            {
+                appName = name + " (\(bundleID))"
+            }
+            
+            return String(format: NSLocalizedString("%@ does not have any app versions.", comment: ""), appName)
+        }
+    }
+}
+
+private extension Error
+{
+    func serialized(withFailure failure: String) -> NSError
+    {
+        // We need to serialize Swift errors thrown during merge conflict to preserve error messages.
+        
+        let serializedError = (self as NSError).withLocalizedFailure(failure).sanitizedForSerialization()
+        
+        var userInfo = serializedError.userInfo
+        userInfo[NSLocalizedDescriptionKey] = nil // Remove NSLocalizedDescriptionKey value to prevent duplicating localized failure in localized description.
+        
+        let error = NSError(domain: serializedError.domain, code: serializedError.code, userInfo: userInfo)
+        return error
+    }
+}
+
 open class MergePolicy: RSTRelationshipPreservingMergePolicy
 {
     open override func resolve(constraintConflicts conflicts: [NSConstraintConflict]) throws
@@ -108,7 +162,15 @@ open class MergePolicy: RSTRelationshipPreservingMergePolicy
                         return indexA < indexB
                     }
                     
-                    databaseObject.setVersions(sortedVersions)
+                    do
+                    {
+                        try databaseObject.setVersions(sortedVersions)
+                    }
+                    catch
+                    {
+                        let nsError = error.serialized(withFailure: NSLocalizedString("AltStore's database could not be saved.", comment: ""))
+                        throw nsError
+                    }
                 }
                 
             case let databaseObject as Source:
@@ -146,8 +208,16 @@ open class MergePolicy: RSTRelationshipPreservingMergePolicy
             switch conflict.databaseObject
             {
             case let databaseObject as StoreApp:
-                // Update versions post-merging to make sure latestSupportedVersion is correct.
-                databaseObject.setVersions(databaseObject.versions)
+                do
+                {
+                    // Update versions post-merging to make sure latestSupportedVersion is correct.
+                    try databaseObject.setVersions(databaseObject.versions)
+                }
+                catch
+                {
+                    let nsError = error.serialized(withFailure: NSLocalizedString("AltStore's database could not be saved.", comment: ""))
+                    throw nsError
+                }
                 
             default: break
             }

AltStoreCore/Model/StoreApp.swift

@@ -267,12 +267,12 @@ public class StoreApp: NSManagedObject, Decodable, Fetchable
                     } else {
                         throw DecodingError.dataCorruptedError(forKey: .downloadURL, in: container, debugDescription: "E downloadURL:String or downloadURLs:[[Platform:URL]] key required.")
                     }
-                    
+
 //                 else {
 //                throw DecodingError.dataCorruptedError(forKey: .downloadURL, in: container, debugDescription: "E downloadURL:String or downloadURLs:[[Platform:URL]] key required.")
 //                }
             }
-            
+
             if let tintColorHex = try container.decodeIfPresent(String.self, forKey: .tintColor)
             {
                 guard let tintColor = UIColor(hexString: tintColorHex) else {
@@ -293,13 +293,13 @@ public class StoreApp: NSManagedObject, Decodable, Fetchable
                 if (versions.count == 0){
                     throw DecodingError.dataCorruptedError(forKey: .versions, in: container, debugDescription: "At least one version is required in key: versions")
                 }
-                
+
                 for version in versions
                 {
                     version.appBundleID = self.bundleIdentifier
                 }
                 
-                self.setVersions(versions)
+                try self.setVersions(versions)
             }
             else
             {
@@ -317,7 +317,7 @@ public class StoreApp: NSManagedObject, Decodable, Fetchable
                                                            size: Int64(size),
                                                            appBundleID: self.bundleIdentifier,
                                                            in: context)
-                self.setVersions([appVersion])
+                try self.setVersions([appVersion])
             }
         }
         catch
@@ -334,8 +334,12 @@ public class StoreApp: NSManagedObject, Decodable, Fetchable
 
 internal extension StoreApp
 {
-    func setVersions(_ versions: [AppVersion])
+    func setVersions(_ versions: [AppVersion]) throws
     {
+        guard let latestVersion = versions.first else {
+            throw MergeError.noVersions(for: self)
+        }
+
         self._versions = NSOrderedSet(array: versions)
         
         let latestSupportedVersion = versions.first(where: { $0.isSupported })
@@ -355,7 +359,6 @@ internal extension StoreApp
         }
                 
         // Preserve backwards compatibility by assigning legacy property values.
-        guard let latestVersion = versions.first else { preconditionFailure("StoreApp must have at least one AppVersion.") }
         self.latestVersionString = latestVersion.version
         self._versionDate = latestVersion.date
         self._versionDescription = latestVersion.localizedDescription
@@ -393,7 +396,7 @@ public extension StoreApp
                                                    appBundleID: app.bundleIdentifier,
                                                    sourceID: Source.altStoreIdentifier,
                                                    in: context)
-        app.setVersions([appVersion])
+        try? app.setVersions([appVersion])
         
         print("makeAltStoreApp StoreApp: \(String(describing: app))")