From fa703a987dcb736a737b63343022169ec103a794 Mon Sep 17 00:00:00 2001
From: Kathleen Dollard <kdollard@microsoft.com>
Date: Mon, 18 May 2020 15:36:13 -0700
Subject: [PATCH 1/2] Sync to upstream

---
 src/System.CommandLine/Option.cs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/System.CommandLine/Option.cs b/src/System.CommandLine/Option.cs
index 75a6910208..74efa6be3c 100644
--- a/src/System.CommandLine/Option.cs
+++ b/src/System.CommandLine/Option.cs
@@ -45,7 +45,7 @@ public virtual Argument Argument
         IArgument IOption.Argument => Argument;
 
         public bool Required { get; set; }
-
+ 
         string IValueDescriptor.ValueName => Name;
 
         Type IValueDescriptor.ValueType => Argument.ArgumentType;

From b2a31a720bdc5c7c49d06a0d6934e47ad506f980 Mon Sep 17 00:00:00 2001
From: Kathleen Dollard <kdollard@microsoft.com>
Date: Wed, 10 Jun 2020 09:19:53 -0700
Subject: [PATCH 2/2] Added ConfigurableCommandLineBuilder

---
 .../Builder/ConfigurableBuilderTests.cs       | 44 +++++++++++++++++++
 .../Builder/CommandBuilder.cs                 | 16 ++++++-
 .../Builder/CommandLineBuilder.cs             |  4 ++
 .../Builder/ConfigurableCommandLineBuilder.cs | 14 ++++++
 4 files changed, 76 insertions(+), 2 deletions(-)
 create mode 100644 src/System.CommandLine.Tests/Builder/ConfigurableBuilderTests.cs
 create mode 100644 src/System.CommandLine/Builder/ConfigurableCommandLineBuilder.cs

diff --git a/src/System.CommandLine.Tests/Builder/ConfigurableBuilderTests.cs b/src/System.CommandLine.Tests/Builder/ConfigurableBuilderTests.cs
new file mode 100644
index 0000000000..0d5fab2d05
--- /dev/null
+++ b/src/System.CommandLine.Tests/Builder/ConfigurableBuilderTests.cs
@@ -0,0 +1,44 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.CommandLine.Builder;
+using FluentAssertions;
+using Xunit;
+
+namespace System.CommandLine.Tests.Builder
+{
+    public class ConfigurableBuilderTests
+    {
+        [Fact]
+        public void When_a_ConfigurableCommandLineBuider_is_created_it_has_a_null_Command()
+        {
+            var builder = new ConfigurableCommandLineBuilder();
+            builder.Command.Should().BeNull();
+        }
+
+        [Fact]
+        public void ConfigurableCommandLineBuider_Command_can_be_set()
+        {
+            var builder = new ConfigurableCommandLineBuilder();
+            builder.SetCommand(new Command("Bob"));
+            builder.Command.Should().NotBeNull()
+                .And.BeEmpty("Bob");
+
+        }
+
+        [Fact]
+        public void ConfigurableCommandLineBuider_Command_should_throw_if_Command_already_set()
+        {
+            var builder = new ConfigurableCommandLineBuilder();
+            builder.SetCommand(new Command("Bob"));
+            Action create = () => builder.SetCommand(new Command("Joe"));
+
+            create.Should()
+                      .Throw<InvalidOperationException>()
+                      .Which
+                      .Message
+                      .Should()
+                      .Be("Command has already been set.");
+        }
+    }
+}
diff --git a/src/System.CommandLine/Builder/CommandBuilder.cs b/src/System.CommandLine/Builder/CommandBuilder.cs
index 8ae8d41a0b..f2bb18ffee 100644
--- a/src/System.CommandLine/Builder/CommandBuilder.cs
+++ b/src/System.CommandLine/Builder/CommandBuilder.cs
@@ -8,15 +8,27 @@ namespace System.CommandLine.Builder
 {
     public class CommandBuilder
     {
-        public CommandBuilder(Command command) 
+        public CommandBuilder(Command command)
         {
             Command = command;
         }
 
-        public Command Command { get; }
+        private protected CommandBuilder()
+        { }
+
+        public Command? Command { get; private set; }
 
         public IEnumerable<Option> Options => Command.Children.OfType<Option>();
 
+        private protected void SetCommandInternal(Command command)
+        {
+            if (!(Command is null))
+            {
+                throw new InvalidOperationException("Command has already been set.");
+            }
+            Command = command;
+        }
+
         internal void AddCommand(Command command) => Command.AddCommand(command);
 
         internal void AddOption(Option option) => Command.AddOption(option);
diff --git a/src/System.CommandLine/Builder/CommandLineBuilder.cs b/src/System.CommandLine/Builder/CommandLineBuilder.cs
index ea175ed5c3..24982f4dfe 100644
--- a/src/System.CommandLine/Builder/CommandLineBuilder.cs
+++ b/src/System.CommandLine/Builder/CommandLineBuilder.cs
@@ -19,6 +19,10 @@ public CommandLineBuilder(Command? rootCommand = null)
         {
         }
 
+        private protected CommandLineBuilder()
+            : base()
+        { }
+
         public bool EnableDirectives { get; set; } = true;
 
         public bool EnablePosixBundling { get; set; } = true;
diff --git a/src/System.CommandLine/Builder/ConfigurableCommandLineBuilder.cs b/src/System.CommandLine/Builder/ConfigurableCommandLineBuilder.cs
new file mode 100644
index 0000000000..6203e10d0e
--- /dev/null
+++ b/src/System.CommandLine/Builder/ConfigurableCommandLineBuilder.cs
@@ -0,0 +1,14 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace System.CommandLine.Builder
+{
+    public class ConfigurableCommandLineBuilder : CommandLineBuilder
+    {
+        public void SetCommand(Command command)
+        {
+            SetCommandInternal(command);
+        }
+
+    }
+}