dotnet run doesn't accept '--' arg separator anymore

When moving from System.CommandLine to the DNX arg parser, we regressed in parsing arguments that should be passed to the underlying process.

Fix #2643

src/dotnet/CommandLine/CommandLineApplication.cs

@@ -44,6 +44,7 @@ namespace Microsoft.DotNet.Cli.CommandLine
         public Func<string> ShortVersionGetter { get; set; }
         public List<CommandLineApplication> Commands { get; private set; }
         public bool HandleResponseFiles { get; set; }
+        public bool AllowArgumentSeparator { get; set; }
 
         public CommandLineApplication Command(string name, Action<CommandLineApplication> configuration,
             bool throwOnUnexpectedArg = true)
@@ -129,10 +130,18 @@ namespace Microsoft.DotNet.Cli.CommandLine
                     if (longOption != null)
                     {
                         processed = true;
-                        option = command.Options.SingleOrDefault(opt => string.Equals(opt.LongName, longOption[0], StringComparison.Ordinal));
+                        string longOptionName = longOption[0];
+                        option = command.Options.SingleOrDefault(opt => string.Equals(opt.LongName, longOptionName, StringComparison.Ordinal));
 
                         if (option == null)
                         {
+                            if (string.IsNullOrEmpty(longOptionName) && !command._throwOnUnexpectedArg && AllowArgumentSeparator)
+                            {
+                                // a stand-alone "--" is the argument separator, so skip it and
+                                // handle the rest of the args as unexpected args
+                                index++;
+                            }
+
                             HandleUnexpectedArg(command, args, index, argTypeName: "option");
                             break;
                         }
@@ -405,6 +414,11 @@ namespace Microsoft.DotNet.Cli.CommandLine
                 }
             }
 
+            if (target.AllowArgumentSeparator)
+            {
+                headerBuilder.Append(" [[--] <arg>...]]");
+            }
+
             headerBuilder.AppendLine();
 
             var nameAndVersion = new StringBuilder();

src/dotnet/commands/dotnet-run/Program.cs

@@ -13,21 +13,18 @@ namespace Microsoft.DotNet.Tools.Run
         {
             DebugHelper.HandleDebugSwitch(ref args);
 
-            CommandLineApplication app = new CommandLineApplication();
+            CommandLineApplication app = new CommandLineApplication(throwOnUnexpectedArg: false);
             app.Name = "dotnet run";
             app.FullName = ".NET Run Command";
             app.Description = "Command used to run .NET apps";
             app.HandleResponseFiles = true;
+            app.AllowArgumentSeparator = true;
             app.HelpOption("-h|--help");
 
             CommandOption framework = app.Option("-f|--framework", "Compile a specific framework", CommandOptionType.SingleValue);
             CommandOption configuration = app.Option("-c|--configuration", "Configuration under which to build", CommandOptionType.SingleValue);
             CommandOption project = app.Option("-p|--project", "The path to the project to run (defaults to the current directory). Can be a path to a project.json or a project directory", CommandOptionType.SingleValue);
 
-            // TODO: this is not supporting args which can be switches (i.e. --test)
-            // TODO: we need to make a change in CommandLine utils or parse args ourselves.
-            CommandArgument runArgs = app.Argument("args", "Arguments to pass to the executable or script", multipleValues: true);
-
             app.OnExecute(() =>
             {
                 RunCommand runCmd = new RunCommand();
@@ -35,7 +32,7 @@ namespace Microsoft.DotNet.Tools.Run
                 runCmd.Framework = framework.Value();
                 runCmd.Configuration = configuration.Value();
                 runCmd.Project = project.Value();
-                runCmd.Args = runArgs.Values;
+                runCmd.Args = app.RemainingArguments;
 
                 return runCmd.Start();
             });