VZVirtualMachineInstance: Rework installRosetta flow (#169)

Because we were installing rosetta directly in the constructor for
VZVirtualMachineInstance, and we'd prefer to not have the constructor
async as it pollutes so much more, we had devised this gnarly callback
approach for the install that is a bit of an eyesore. This changes focus
is on moving the install flow to a method that is already async so we
can piggyback off of it, and removing the install logic from the config
-> VZConfig conversion. Now the install will occur during start() if
rosetta is not installed.

Sources/Containerization/VZVirtualMachineInstance.swift

@@ -131,6 +131,9 @@ extension VZVirtualMachineInstance {
                 )
             }
 
+            // Do any necessary setup needed prior to starting the guest.
+            try await self.prestart()
+
             try await self.vm.start(queue: self.queue)
 
             let agent = Vminitd(
@@ -203,23 +206,19 @@ extension VZVirtualMachineInstance {
             port: port
         )
     }
+
+    func prestart() async throws {
+        if self.config.rosetta && VZLinuxRosettaDirectoryShare.availability == .notInstalled {
+            self.logger?.info("installing rosetta")
+            try await VZVirtualMachineInstance.Configuration.installRosetta()
+        }
+    }
 }
 
 extension VZVirtualMachineInstance.Configuration {
-    public static func installRosetta() throws {
-        #if arch(arm64)
+    public static func installRosetta() async throws {
         do {
-            let _err: Mutex<Swift.Error?> = .init(nil)
-            VZLinuxRosettaDirectoryShare.installRosetta(completionHandler: { error in
-                _err.withLock {
-                    $0 = error
-                }
-            })
-            let err = _err.withLock { $0 }
-            guard let err else {
-                return
-            }
-            throw err
+            try await VZLinuxRosettaDirectoryShare.installRosetta()
         } catch {
             throw ContainerizationError(
                 .internalError,
@@ -227,8 +226,8 @@ extension VZVirtualMachineInstance.Configuration {
                 cause: error
             )
         }
-        #endif
     }
+
     private func serialPort(path: URL) throws -> [VZVirtioConsoleDeviceSerialPortConfiguration] {
         let c = VZVirtioConsoleDeviceSerialPortConfiguration()
         c.attachment = try VZFileSerialPortAttachment(url: path, append: true)
@@ -261,7 +260,8 @@ extension VZVirtualMachineInstance.Configuration {
                     message: "rosetta was requested but is not supported on this machine"
                 )
             case .notInstalled:
-                try Self.installRosetta()
+                // NOTE: If rosetta isn't installed, we'll error with a nice error message
+                // during .start() of the virtual machine instance.
                 fallthrough
             case .installed:
                 let share = try VZLinuxRosettaDirectoryShare()