fix #1551

Author: jonsequitur

src/System.CommandLine.Tests/ArgumentTests.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Collections.Generic;
-using System.CommandLine.Invocation;
 using System.CommandLine.Parsing;
 using System.IO;
 using FluentAssertions;

src/System.CommandLine.Tests/ParserTests.cs

@@ -1642,25 +1642,21 @@ public void A_subcommand_wont_overflow_when_checking_maximum_argument_capcity()
             act.Should().NotThrow();
         }
 
-        [Fact] // https://github.com/dotnet/command-line-api/issues/1533
-        public void Empty_strings_in_parsed_args_array_are_ignored()
+        [Theory] // https://github.com/dotnet/command-line-api/issues/1551, https://github.com/dotnet/command-line-api/issues/1533
+        [InlineData("--exec-prefix", "")]
+        [InlineData("--exec-prefix:", "")]
+        [InlineData("--exec-prefix=", "")]
+        public void Parsed_value_of_empty_string_arg_is_an_empty_string(string arg1, string arg2)
         {
-            var option = new Option<int>("-x");
-            var subcommand = new Command("sub")
+            var option = new Option<string>("--exec-prefix", getDefaultValue: () => "/usr/local");
+            var rootCommand = new RootCommand
             {
                 option
             };
-            var command = new RootCommand
-            {
-                subcommand
-            };
-
-            var result = command.Parse("", "sub", "", "-x", "123");
 
-            result.Errors.Should().BeEmpty();
+            var result = rootCommand.Parse(new[] { arg1, arg2 });
 
-            result.CommandResult.Command.Should().BeSameAs(subcommand);
-            result.FindResultFor(option).Should().NotBeNull();
+            result.GetValueForOption(option).Should().BeEmpty();
         }
     }
 }

src/System.CommandLine/Parsing/StringExtensions.cs

@@ -171,16 +171,13 @@ internal static TokenizeResult Tokenize(
                         tokenList.Add(Argument(rest));
                     }
                 }
-                else if (configuration.EnablePosixBundling &&
-                         CanBeUnbundled(arg) && 
-                         TryUnbundle(arg.AsSpan(1), i))
-                {
-                }
-                else if (arg.Length > 0)
+                else if (!configuration.EnablePosixBundling ||
+                         !CanBeUnbundled(arg) ||
+                         !TryUnbundle(arg.AsSpan(1), i))
                 {
                     tokenList.Add(Argument(arg));
                 }
-
+              
                 Token Argument(string value) => new(value, TokenType.Argument, default, i);
 
                 Token CommandArgument(string value, Command command) => new(value, TokenType.Argument, command, i);
@@ -203,7 +200,7 @@ internal static TokenizeResult Tokenize(
             bool CanBeUnbundled(string arg)
                 => arg.Length > 2 
                     && arg[0] == '-'
-                    && char.IsLetter(arg[1]) // don't check for "--" prefixed args
+                    && arg[1]  != '-'// don't check for "--" prefixed args
                     && arg[2] != ':' && arg[2] != '=' // handled by TrySplitIntoSubtokens
                     && !PreviousTokenIsAnOptionExpectingAnArgument(out _);