Sort suggestions by match index, then alphabetically

Author: kimsey0

src/System.CommandLine/Parsing/StringExtensions.cs

@@ -15,13 +15,18 @@ public static class StringExtensions
         private static readonly string[] _optionPrefixStrings = { "--", "-", "/" };
 
         internal static bool ContainsCaseInsensitive(
+            this string source,
+            string value) =>
+            source.IndexOfCaseInsensitive(value) >= 0;
+
+        internal static int IndexOfCaseInsensitive(
             this string source,
             string value) =>
             CultureInfo.InvariantCulture
                        .CompareInfo
                        .IndexOf(source,
                                 value ?? "",
-                                CompareOptions.OrdinalIgnoreCase) >= 0;
+                                CompareOptions.OrdinalIgnoreCase);
 
         internal static string RemovePrefix(this string rawAlias)
         {

src/System.CommandLine/Symbol.cs

@@ -146,8 +146,9 @@ public virtual IEnumerable<string> GetSuggestions(string textToMatch = null)
             return this.ChildSymbolAliases()
                        .Concat(argumentSuggestions)
                        .Distinct()
-                       .OrderBy(symbol => symbol, StringComparer.OrdinalIgnoreCase)
-                       .Containing(textToMatch);
+                       .Containing(textToMatch)
+                       .OrderBy(symbol => symbol.IndexOfCaseInsensitive(textToMatch))
+                       .ThenBy(symbol => symbol, StringComparer.OrdinalIgnoreCase);
         }
 
         public override string ToString() => $"{GetType().Name}: {Name}";