tart run: deprecate --with-softnet and introduce --net-softnet (#274)

Sources/tart/Commands/Run.swift

@@ -37,7 +37,8 @@ struct Run: AsyncParsableCommand {
       + "Note that this feature is experimental and there may be bugs present when using VNC."))
   var vncExperimental: Bool = false
 
-  @Flag var withSoftnet: Bool = false
+  @Flag(help: ArgumentHelp(visibility: .private))
+  var withSoftnet: Bool = false
 
   @Option(help: ArgumentHelp("""
     Additional disk attachments with an optional read-only specifier\n(e.g. --disk=\"disk.bin\" --disk=\"ubuntu.iso:ro\")
@@ -64,6 +65,10 @@ struct Run: AsyncParsableCommand {
                                               """, valueName: "interface name"))
   var netBridged: String?
 
+  @Flag(help: ArgumentHelp("Use software networking instead of the default shared (NAT) networking",
+          discussion: "Learn how to configure Softnet for use with Tart here: https://github.com/cirruslabs/softnet"))
+  var netSoftnet: Bool = false
+
   func validate() throws {
     if vnc && vncExperimental {
       throw ValidationError("--vnc and --vnc-experimental are mutually exclusive")
@@ -73,6 +78,10 @@ struct Run: AsyncParsableCommand {
       throw ValidationError("--with-softnet and --net-bridged are mutually exclusive")
     }
 
+    if netBridged != nil && netSoftnet {
+      throw ValidationError("--net-bridged and --net-softnet are mutually exclusive")
+    }
+
     if graphics && noGraphics {
       throw ValidationError("--graphics and --no-graphics are mutually exclusive")
     }
@@ -145,7 +154,7 @@ struct Run: AsyncParsableCommand {
   }
 
   func userSpecifiedNetwork(vmDir: VMDirectory) throws -> Network? {
-    if withSoftnet {
+    if withSoftnet || netSoftnet {
       let config = try VMConfig.init(fromURL: vmDir.configURL)
 
       return try Softnet(vmMACAddress: config.macAddress.string)