From 2557b0c9b7f2173831f779e5aa491ac9e7b828c2 Mon Sep 17 00:00:00 2001
From: Jon Sequeira <jonsequeira@gmail.com>
Date: Tue, 5 Jan 2021 08:28:29 -0800
Subject: [PATCH] fix #1135

---
 .../SuggestionTests.cs                        |  2 +-
 src/System.CommandLine/Argument.cs            |  6 ++--
 .../Builder/CommandLineBuilderExtensions.cs   |  1 -
 .../SuggestionSourceExtensions.cs             |  5 ++-
 .../SuggestionSourceList.cs                   | 32 +++++++++++++++++++
 5 files changed, 38 insertions(+), 8 deletions(-)
 create mode 100644 src/System.CommandLine/SuggestionSourceList.cs

diff --git a/src/System.CommandLine.Tests/SuggestionTests.cs b/src/System.CommandLine.Tests/SuggestionTests.cs
index ef982a1899..895a2a36da 100644
--- a/src/System.CommandLine.Tests/SuggestionTests.cs
+++ b/src/System.CommandLine.Tests/SuggestionTests.cs
@@ -987,7 +987,7 @@ public void Enum_suggestions_can_be_configured_without_list_clear()
             {
                 var command = new Command("the-command")
                 {
-                    new Argument<DayOfWeek?>()
+                    new Argument<DayOfWeek?>
                     {
                         Suggestions = { "mon", "tues", "wed", "thur", "fri", "sat", "sun" }
                     }
diff --git a/src/System.CommandLine/Argument.cs b/src/System.CommandLine/Argument.cs
index deadaf161f..aad1f9f2a9 100644
--- a/src/System.CommandLine/Argument.cs
+++ b/src/System.CommandLine/Argument.cs
@@ -19,7 +19,7 @@ public class Argument : Symbol, IArgument
         private IArgumentArity? _arity;
         private TryConvertArgument? _convertArguments;
         private Type _argumentType = typeof(string);
-        private List<ISuggestionSource>? _suggestions = null;
+        private SuggestionSourceList? _suggestions = null;
 
         /// <summary>
         /// Initializes a new instance of the Argument class.
@@ -93,13 +93,13 @@ internal TryConvertArgument? ConvertArguments
         /// <summary>
         /// Gets the list of suggestion sources for the argument.
         /// </summary>
-        public List<ISuggestionSource> Suggestions
+        public SuggestionSourceList Suggestions
         { 
             get
             {
                 if (_suggestions is null)
                 {
-                    _suggestions = new List<ISuggestionSource>
+                    _suggestions = new SuggestionSourceList
                     {
                         SuggestionSource.ForType(ArgumentType)
                     };
diff --git a/src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs b/src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs
index 4aebaf3a5a..4e193ea527 100644
--- a/src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs
+++ b/src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs
@@ -10,7 +10,6 @@
 using System.IO;
 using System.Linq;
 using System.Reflection;
-using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using static System.Environment;
diff --git a/src/System.CommandLine/SuggestionSourceExtensions.cs b/src/System.CommandLine/SuggestionSourceExtensions.cs
index 431db3460f..11c56c1dc7 100644
--- a/src/System.CommandLine/SuggestionSourceExtensions.cs
+++ b/src/System.CommandLine/SuggestionSourceExtensions.cs
@@ -1,7 +1,6 @@
 // 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.Collections.Generic;
 using System.CommandLine.Suggestions;
 
 namespace System.CommandLine
@@ -9,7 +8,7 @@ namespace System.CommandLine
     public static class SuggestionSourceExtensions
     {
         public static void Add(
-            this List<ISuggestionSource> suggestionSources,
+            this SuggestionSourceList suggestionSources,
             SuggestDelegate suggest)
         {
             if (suggestionSources is null)
@@ -26,7 +25,7 @@ public static void Add(
         }
 
         public static void Add(
-            this List<ISuggestionSource> suggestionSources,
+            this SuggestionSourceList suggestionSources,
             params string[] suggestions)
         {
             if (suggestionSources is null)
diff --git a/src/System.CommandLine/SuggestionSourceList.cs b/src/System.CommandLine/SuggestionSourceList.cs
new file mode 100644
index 0000000000..610b36eb27
--- /dev/null
+++ b/src/System.CommandLine/SuggestionSourceList.cs
@@ -0,0 +1,32 @@
+// // 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.Collections;
+using System.Collections.Generic;
+using System.CommandLine.Suggestions;
+
+namespace System.CommandLine
+{
+    public class SuggestionSourceList : IReadOnlyList<ISuggestionSource>
+    {
+        private readonly List<ISuggestionSource> _sources = new List<ISuggestionSource>();
+
+        public void Add(ISuggestionSource source)
+        {
+            _sources.Add(source);
+        }
+
+        public IEnumerator<ISuggestionSource> GetEnumerator() => _sources.GetEnumerator();
+
+        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+        public void Clear()
+        {
+            _sources.Clear();
+        }
+
+        public int Count => _sources.Count;
+
+        public ISuggestionSource this[int index] => _sources[index];
+    }
+}
\ No newline at end of file