⚠️ Add a temporary warning about macOS Monterey

Sources/MasKit/AppStore/Downloader.swift

@@ -51,7 +51,7 @@ private func downloadWithRetries(
 
         let attempts = attempts - 1
         printWarning((downloadError ?? error).localizedDescription)
-        print("Trying again up to \(attempts) more \(attempts == 1 ? "time" : "times").")
+        printWarning("Trying again up to \(attempts) more \(attempts == 1 ? "time" : "times").")
         return downloadWithRetries(appID, purchase: purchase, attempts: attempts)
     }
 }

Sources/MasKit/Commands/Open.swift

@@ -50,7 +50,7 @@ public struct OpenCommand: CommandProtocol {
 
             guard let appId = Int(options.appId)
             else {
-                print("Invalid app ID")
+                printError("Invalid app ID")
                 return .failure(.noSearchResultsFound)
             }
 

Sources/MasKit/Formatters/Utilities.swift

@@ -19,7 +19,11 @@ let csi = "\u{001B}["
 
     // Override global print for testability.
     // See MasKitTests/OutputListener.swift.
-    func print(_ items: Any..., separator: String = " ", terminator: String = "\n") {
+    func print(
+        _ items: Any...,
+        separator: String = " ",
+        terminator: String = "\n"
+    ) {
         if let observer = printObserver {
             let output =
                 items
@@ -39,8 +43,42 @@ let csi = "\u{001B}["
         Swift.print(terminator, terminator: "")
     }
 
+    func print<Target>(
+        _ items: Any...,
+        separator: String = " ",
+        terminator: String = "\n",
+        to output: inout Target
+    ) where Target: TextOutputStream {
+        if let observer = printObserver {
+            let output =
+                items
+                .map { "\($0)" }
+                .joined(separator: separator)
+                .appending(terminator)
+            observer(output)
+        }
+
+        var prefix = ""
+        for item in items {
+            Swift.print(prefix, terminator: "", to: &output)
+            Swift.print(item, terminator: "", to: &output)
+            prefix = separator
+        }
+
+        Swift.print(terminator, terminator: "", to: &output)
+    }
+
 #endif
 
+private var standardError = FileHandle.standardError
+
+extension FileHandle: TextOutputStream {
+    public func write(_ string: String) {
+        guard let data = string.data(using: .utf8) else { return }
+        write(data)
+    }
+}
+
 func printInfo(_ message: String) {
     guard isatty(fileno(stdout)) != 0 else {
         print("==> \(message)")
@@ -51,30 +89,31 @@ func printInfo(_ message: String) {
     print("\(csi)1;34m==>\(csi)0m \(csi)1m\(message)\(csi)0m")
 }
 
-func printWarning(_ message: String) {
-    guard isatty(fileno(stdout)) != 0 else {
-        print("Warning: \(message)")
+public func printWarning(_ message: String) {
+    guard isatty(fileno(stderr)) != 0 else {
+        print("Warning: \(message)", to: &standardError)
         return
     }
 
     // Yellow, underlined "Warning:" prefix
-    print("\(csi)4;33mWarning:\(csi)0m \(message)")
+    print("\(csi)4;33mWarning:\(csi)0m \(message)", to: &standardError)
 }
 
 public func printError(_ message: String) {
-    guard isatty(fileno(stdout)) != 0 else {
-        print("Error: \(message)")
+    guard isatty(fileno(stderr)) != 0 else {
+        print("Error: \(message)", to: &standardError)
         return
     }
 
     // Red, underlined "Error:" prefix
-    print("\(csi)4;31mError:\(csi)0m \(message)")
+    print("\(csi)4;31mError:\(csi)0m \(message)", to: &standardError)
 }
 
 func clearLine() {
     guard isatty(fileno(stdout)) != 0 else {
         return
     }
+
     print("\(csi)2K\(csi)0G", terminator: "")
     fflush(stdout)
 }

Sources/MasKit/Models/SoftwareProduct.swift

@@ -31,8 +31,11 @@ extension SoftwareProduct {
         // Only look at min OS version if we have one, also only consider macOS apps
         // Replace string literal with MasStoreSearch.Entity once `search` branch is merged.
         if let osVersion = Version(tolerant: storeApp.minimumOsVersion), storeApp.kind == "mac-software" {
-            let requiredVersion = OperatingSystemVersion(majorVersion: osVersion.major, minorVersion: osVersion.minor,
-                                                         patchVersion: osVersion.patch)
+            let requiredVersion = OperatingSystemVersion(
+                majorVersion: osVersion.major,
+                minorVersion: osVersion.minor,
+                patchVersion: osVersion.patch
+            )
             // Don't consider an app outdated if the version in the app store requires a higher OS version.
             guard ProcessInfo.processInfo.isOperatingSystemAtLeast(requiredVersion) else {
                 return false

Sources/mas/main.swift

@@ -7,10 +7,19 @@
 //
 
 import Commandant
+import Foundation
 import MasKit
 
 MasKit.initialize()
 
+let monterey = OperatingSystemVersion(majorVersion: 12, minorVersion: 0, patchVersion: 0)
+if ProcessInfo.processInfo.isOperatingSystemAtLeast(monterey) {
+    printWarning(
+        "mas is not yet functional on macOS Monterey (12) due to changes in macOS frameworks. "
+            + "To track progress or to *contribute* to fixing this issue, please see: "
+            + "https://github.com/mas-cli/mas/issues/417")
+}
+
 let registry = CommandRegistry<MASError>()
 let helpCommand = HelpCommand(registry: registry)
 

Tests/MasKitTests/Models/SoftwareProductSpec.swift

@@ -18,8 +18,13 @@ public class SoftwareProductSpec: QuickSpec {
             MasKit.initialize()
         }
         describe("software product") {
-            let app = SoftwareProductMock(appName: "App", bundleIdentifier: "", bundlePath: "", bundleVersion: "1.0.0",
-                                          itemIdentifier: 111)
+            let app = SoftwareProductMock(
+                appName: "App",
+                bundleIdentifier: "",
+                bundlePath: "",
+                bundleVersion: "1.0.0",
+                itemIdentifier: 111
+            )
 
             let currentApp = SearchResult(kind: "mac-software", version: "1.0.0")
             let appUpdate = SearchResult(kind: "mac-software", version: "2.0.0")