refactor and add tests for null / empty tokens when default value is used

Author: jonsequitur

src/System.CommandLine.Tests/ParseDiagramTests.cs

@@ -90,7 +90,6 @@ public void Parse_diagram_identifies_options_where_default_values_have_been_appl
                 }
             };
 
-
             var result = rootCommand.Parse("-w 9000");
 
             var diagram = result.Diagram();

src/System.CommandLine.Tests/ParserTests.cs

@@ -1371,6 +1371,45 @@ public void When_an_option_with_a_default_value_is_not_matched_then_the_option_r
                   .BeTrue();
         }
 
+        [Fact]
+        public void When_an_option_with_a_default_value_is_not_matched_then_there_are_no_tokens()
+        {
+            var option = new Option<string>(
+                "-o", 
+                () => "the-default");
+
+            var command = new Command("command")
+            {
+                option
+            };
+
+            var result = command.Parse("command");
+
+            result.FindResultFor(option)
+                  .Token
+                  .Should()
+                  .BeNull();
+        }
+
+        [Fact]
+        public void When_an_argument_with_a_default_value_is_not_matched_then_there_are_no_tokens()
+        {
+            var argument = new Argument<string>(
+                "o", 
+                () => "the-default");
+
+            var command = new Command("command")
+            {
+                argument
+            };
+            var result = command.Parse("command");
+
+            result.FindResultFor(argument)
+                  .Tokens
+                  .Should()
+                  .BeEmpty();
+        }
+
         [Fact]
         public void Command_default_argument_value_does_not_override_parsed_value()
         {

src/System.CommandLine/Parsing/OptionResult.cs

@@ -12,18 +12,18 @@ public class OptionResult : SymbolResult
 
         internal OptionResult(
             IOption option,
-            Token token,
-            CommandResult parent) :
+            Token token = null,
+            CommandResult parent = null) :
             base(option ?? throw new ArgumentNullException(nameof(option)),
                  parent)
         {
             Option = option;
-            Token = token ?? throw new ArgumentNullException(nameof(token));
+            Token = token;
         }
 
         public IOption Option { get; }
 
-        public bool IsImplicit => Token is ImplicitToken;
+        public bool IsImplicit => Token is ImplicitToken || Token is null;
 
         public Token Token { get; }
 

src/System.CommandLine/Parsing/ParseResultVisitor.cs

@@ -318,7 +318,7 @@ private void PopulateDefaultValues()
 
                                 var optionResult = new OptionResult(
                                     option,
-                                    option.CreateImplicitToken(),
+                                    null,
                                     commandResult);
 
                                 var childArgumentResult = optionResult.GetOrCreateDefaultArgumentResult(

src/System.CommandLine/Parsing/SymbolResultExtensions.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Collections.Generic;
+using System.Linq;
 
 namespace System.CommandLine.Parsing
 {
@@ -24,12 +25,24 @@ internal static IEnumerable<SymbolResult> AllSymbolResults(this SymbolResult sym
             }
         }
 
-        internal static Token Token(this SymbolResult symbolResult) =>
-            symbolResult switch
+        internal static Token Token(this SymbolResult symbolResult)
+        {
+            return symbolResult switch
             {
                 CommandResult commandResult => commandResult.Token,
-                OptionResult optionResult => optionResult.Token,
+                OptionResult optionResult => optionResult.Token ??
+                                             CreateImplicitToken(optionResult.Option),
                 _ => throw new ArgumentOutOfRangeException(nameof(symbolResult))
             };
+
+            Token CreateImplicitToken(IOption option)
+            {
+                var optionName = option.Name;
+
+                var defaultAlias = option.RawAliases.First(alias => alias.RemovePrefix() == optionName);
+
+                return new ImplicitToken(defaultAlias, TokenType.Option);
+            }
+        }
     }
-}
+}

src/System.CommandLine/SymbolExtensions.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.Parsing;
 using System.Linq;
 
 namespace System.CommandLine
@@ -11,8 +10,8 @@ internal static class SymbolExtensions
     {
         internal static IEnumerable<string> ChildSymbolAliases(this ISymbol symbol) =>
             symbol.Children
-                .Where(s => !s.IsHidden)
-                .SelectMany(s => s.RawAliases);
+                  .Where(s => !s.IsHidden)
+                  .SelectMany(s => s.RawAliases);
 
         internal static IEnumerable<IArgument> Arguments(this ISymbol symbol)
         {
@@ -34,14 +33,5 @@ internal static IEnumerable<IArgument> Arguments(this ISymbol symbol)
                     throw new NotSupportedException();
             }
         }
-
-        internal static Token CreateImplicitToken(this IOption option)
-        {
-            var optionName = option.Name;
-
-            var defaultAlias = option.RawAliases.First(alias => alias.RemovePrefix() == optionName);
-
-            return new ImplicitToken(defaultAlias, TokenType.Option);
-        }
     }
-}
+}