Downloads latest _available_ version when updating from AppViewController

Asks user to fall back to latest supported verson if version is not compatible with device’s iOS version.

AltStore/App Detail/AppViewController.swift

@@ -360,13 +360,21 @@ private extension AppViewController
 {
     func update()
     {
+        var buttonAction: AppBannerView.AppAction?
+        
+        if let installedApp = self.app.installedApp, let latestVersion = self.app.latestAvailableVersion, !installedApp.matches(latestVersion)
+        {
+            // Explicitly set button action to .update if there is an update available, even if it's not supported.
+            buttonAction = .update
+        }
+        
         for button in [self.bannerView.button!, self.navigationBarDownloadButton!]
         {
             button.tintColor = self.app.tintColor
             button.isIndicatingActivity = false
         }
         
-        self.bannerView.configure(for: self.app)
+        self.bannerView.configure(for: self.app, action: buttonAction)
         
         let title = self.bannerView.button.title(for: .normal)
         self.navigationBarDownloadButton.setTitle(title, for: .normal)
@@ -498,9 +506,9 @@ extension AppViewController
     {
         if let installedApp = self.app.installedApp
         {
-            if let latestVersion = self.app.latestSupportedVersion, !installedApp.matches(latestVersion)
+            if let latestVersion = self.app.latestAvailableVersion, !installedApp.matches(latestVersion)
             {
-                self.updateApp(installedApp)
+                self.updateApp(installedApp, to: latestVersion)
             }
             else
             {
@@ -551,7 +559,7 @@ extension AppViewController
         UIApplication.shared.open(installedApp.openAppURL)
     }
     
-    func updateApp(_ installedApp: InstalledApp)
+    func updateApp(_ installedApp: InstalledApp, to version: AppVersion)
     {
         let previousProgress = AppManager.shared.installationProgress(for: installedApp)
         guard previousProgress == nil else {
@@ -560,7 +568,7 @@ extension AppViewController
             return
         }
         
-        _ = AppManager.shared.update(installedApp, presentingViewController: self) { (result) in
+        AppManager.shared.update(installedApp, to: version, presentingViewController: self) { (result) in
             DispatchQueue.main.async {
                 switch result
                 {

AltStore/Managing Apps/AppManager.swift

@@ -557,9 +557,9 @@ extension AppManager
     }
     
     @discardableResult
-    func update(_ installedApp: InstalledApp, presentingViewController: UIViewController?, context: AuthenticatedOperationContext = AuthenticatedOperationContext(), completionHandler: @escaping (Result<InstalledApp, Error>) -> Void) -> Progress
+    func update(_ installedApp: InstalledApp, to version: AppVersion? = nil, presentingViewController: UIViewController?, context: AuthenticatedOperationContext = AuthenticatedOperationContext(), completionHandler: @escaping (Result<InstalledApp, Error>) -> Void) -> Progress
     {
-        guard let appVersion = installedApp.storeApp?.latestSupportedVersion else {
+        guard let appVersion = version ?? installedApp.storeApp?.latestSupportedVersion else {
             completionHandler(.failure(OperationError.appNotFound(name: installedApp.name)))
             return Progress.discreteProgress(totalUnitCount: 1)
         }

AltStore/Operations/DownloadAppOperation.swift

@@ -17,7 +17,9 @@ import Roxas
 @objc(DownloadAppOperation)
 class DownloadAppOperation: ResultOperation<ALTApplication>
 {
-    let app: AppProtocol
+    @Managed
+    private(set) var app: AppProtocol
+    
     let context: InstallAppOperationContext
     
     private let appName: String
@@ -59,22 +61,36 @@ class DownloadAppOperation: ResultOperation<ALTApplication>
         // Set _after_ checking self.context.error to prevent overwriting localized failure for previous errors.
         self.localizedFailure = String(format: NSLocalizedString("%@ could not be downloaded.", comment: ""), self.appName)
         
-        guard let storeApp = self.app as? StoreApp else {
+        self.$app.perform { app in
-            // Only StoreApp allows falling back to previous versions.
-            // AppVersion can only install itself, and ALTApplication doesn't have previous versions.
-            return self.download(self.app)
-        }
-        
-        // Verify storeApp
-        storeApp.managedObjectContext?.perform {
             do
             {
-                let latestVersion = try self.verify(storeApp)
+                var appVersion: AppVersion?
-                self.download(latestVersion)
+                
+                if let version = app as? AppVersion
+                {
+                    appVersion = version
+                }
+                else if let storeApp = app as? StoreApp
+                {
+                    guard let latestVersion = storeApp.latestAvailableVersion else {
+                        let failureReason = String(format: NSLocalizedString("The latest version of %@ could not be determined.", comment: ""), self.appName)
+                        throw OperationError.unknown(failureReason: failureReason)
+                    }
+                    
+                    // Attempt to download latest _available_ version, and fall back to older versions if necessary.
+                    appVersion = latestVersion
+                }
+                
+                if let appVersion
+                {
+                    try self.verify(appVersion)
+                }
+                
+                self.download(appVersion ?? app)
             }
             catch let error as VerificationError where error.code == .iOSVersionNotSupported
             {
-                guard let presentingViewController = self.context.presentingViewController, let latestSupportedVersion = storeApp.latestSupportedVersion
+                guard let presentingViewController = self.context.presentingViewController, let storeApp = app.storeApp, let latestSupportedVersion = storeApp.latestSupportedVersion
                 else { return self.finish(.failure(error)) }
                 
                 if let installedApp = storeApp.installedApp
@@ -121,23 +137,16 @@ class DownloadAppOperation: ResultOperation<ALTApplication>
 
 private extension DownloadAppOperation
 {
-    func verify(_ storeApp: StoreApp) throws -> AppVersion
+    func verify(_ version: AppVersion) throws
     {
-        guard let version = storeApp.latestAvailableVersion else {
-            let failureReason = String(format: NSLocalizedString("The latest version of %@ could not be determined.", comment: ""), self.appName)
-            throw OperationError.unknown(failureReason: failureReason)
-        }
-        
         if let minOSVersion = version.minOSVersion, !ProcessInfo.processInfo.isOperatingSystemAtLeast(minOSVersion)
         {
-            throw VerificationError.iOSVersionNotSupported(app: storeApp, requiredOSVersion: minOSVersion)
+            throw VerificationError.iOSVersionNotSupported(app: version, requiredOSVersion: minOSVersion)
         }
         else if let maxOSVersion = version.maxOSVersion, ProcessInfo.processInfo.operatingSystemVersion > maxOSVersion
         {
-            throw VerificationError.iOSVersionNotSupported(app: storeApp, requiredOSVersion: maxOSVersion)
+            throw VerificationError.iOSVersionNotSupported(app: version, requiredOSVersion: maxOSVersion)
         }
-        
-        return version
     }
     
     func download(@Managed _ app: AppProtocol)