From e6cc70edf84dcbdfc0ab5fb440c9f29d8027eb1c Mon Sep 17 00:00:00 2001
From: Adam Sitnik <adam.sitnik@gmail.com>
Date: Wed, 18 Jan 2023 11:41:51 +0100
Subject: [PATCH 1/5] LocalizationResources should be readonly and same for
 entire symbol tree

---
 ...ests.System_CommandLine_api_is_not_changed.approved.txt | 2 +-
 src/System.CommandLine/Parsing/ParseResultVisitor.cs       | 5 ++---
 src/System.CommandLine/Parsing/RootCommandResult.cs        | 7 ++++++-
 src/System.CommandLine/Parsing/SymbolResult.cs             | 7 +------
 4 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
index 609adccecc..0467a52a2d 100644
--- a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
+++ b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
@@ -424,7 +424,7 @@ System.CommandLine.Parsing
   public abstract class SymbolResult
     public System.Collections.Generic.IReadOnlyList<SymbolResult> Children { get; }
     public System.String ErrorMessage { get; set; }
-    public System.CommandLine.LocalizationResources LocalizationResources { get; set; }
+    public System.CommandLine.LocalizationResources LocalizationResources { get; }
     public SymbolResult Parent { get; }
     public System.CommandLine.Symbol Symbol { get; }
     public System.Collections.Generic.IReadOnlyList<Token> Tokens { get; }
diff --git a/src/System.CommandLine/Parsing/ParseResultVisitor.cs b/src/System.CommandLine/Parsing/ParseResultVisitor.cs
index 53d7d5b48b..a5b52ed438 100644
--- a/src/System.CommandLine/Parsing/ParseResultVisitor.cs
+++ b/src/System.CommandLine/Parsing/ParseResultVisitor.cs
@@ -121,9 +121,8 @@ private void VisitRootCommandNode(CommandNode rootCommandNode)
             _rootCommandResult = new RootCommandResult(
                 rootCommandNode.Command,
                 rootCommandNode.Token,
-                _symbolResults);
-
-            _rootCommandResult.LocalizationResources = _parser.Configuration.LocalizationResources;
+                _symbolResults,
+                _parser.Configuration.LocalizationResources ?? LocalizationResources.Instance);
 
             _innermostCommandResult = _rootCommandResult;
         }
diff --git a/src/System.CommandLine/Parsing/RootCommandResult.cs b/src/System.CommandLine/Parsing/RootCommandResult.cs
index 2f7888005e..680db15df5 100644
--- a/src/System.CommandLine/Parsing/RootCommandResult.cs
+++ b/src/System.CommandLine/Parsing/RootCommandResult.cs
@@ -8,15 +8,20 @@ namespace System.CommandLine.Parsing
     internal sealed class RootCommandResult : CommandResult
     {
         private readonly Dictionary<Symbol, SymbolResult> _symbolResults;
+        private readonly LocalizationResources _localizationResources;
 
         public RootCommandResult(
             Command command,
             Token token,
-            Dictionary<Symbol, SymbolResult> symbolResults) : base(command, token)
+            Dictionary<Symbol, SymbolResult> symbolResults,
+            LocalizationResources localizationResources) : base(command, token)
         {
             _symbolResults = symbolResults;
+            _localizationResources = localizationResources;
         }
 
+        public override LocalizationResources LocalizationResources => _localizationResources;
+
         public override ArgumentResult? FindResultFor(Argument argument)
             => _symbolResults.TryGetValue(argument, out SymbolResult? result) ? (ArgumentResult)result : default;
 
diff --git a/src/System.CommandLine/Parsing/SymbolResult.cs b/src/System.CommandLine/Parsing/SymbolResult.cs
index 433477ece7..367e28ad52 100644
--- a/src/System.CommandLine/Parsing/SymbolResult.cs
+++ b/src/System.CommandLine/Parsing/SymbolResult.cs
@@ -15,7 +15,6 @@ public abstract class SymbolResult
     {
         private List<SymbolResult>? _children;
         private protected List<Token>? _tokens;
-        private LocalizationResources? _resources;
 
         private protected SymbolResult(
             Symbol symbol, 
@@ -95,11 +94,7 @@ internal int MaximumArgumentCapacity
         /// <summary>
         /// Localization resources used to produce messages for this symbol result.
         /// </summary>
-        public LocalizationResources LocalizationResources
-        {
-            get => _resources ??= Parent?.LocalizationResources ?? LocalizationResources.Instance;
-            set => _resources = value;
-        }
+        public virtual LocalizationResources LocalizationResources => GetRoot().LocalizationResources;
 
         internal void AddToken(Token token) => (_tokens ??= new()).Add(token);
 

From 4d93e7a0bcce00a31f8228a463d311cd8ee37586 Mon Sep 17 00:00:00 2001
From: Adam Sitnik <adam.sitnik@gmail.com>
Date: Wed, 18 Jan 2023 13:00:31 +0100
Subject: [PATCH 2/5] remove Symbol from SymbolResult, as each derived type
 defines more specific property anyway

---
 ...ommandLine_api_is_not_changed.approved.txt |  1 -
 src/System.CommandLine.Tests/ArgumentTests.cs | 23 +++++---
 src/System.CommandLine.Tests/CommandTests.cs  | 19 +++++--
 .../ParseResultTests.cs                       |  4 +-
 .../ParserTests.MultiplePositions.cs          | 11 +++-
 src/System.CommandLine.Tests/ParserTests.cs   | 20 +++----
 .../ParsingValidationTests.cs                 | 56 +++++++++----------
 .../Builder/CommandLineBuilderExtensions.cs   |  4 +-
 src/System.CommandLine/Help/VersionOption.cs  |  6 +-
 src/System.CommandLine/ParseResult.cs         |  9 ++-
 .../Parsing/ArgumentResult.cs                 |  6 +-
 .../Parsing/CommandResult.cs                  | 25 ++++++++-
 .../Parsing/OptionResult.cs                   |  7 ++-
 .../Parsing/SymbolResult.cs                   | 44 +--------------
 14 files changed, 124 insertions(+), 111 deletions(-)

diff --git a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
index 0467a52a2d..d4fb931a66 100644
--- a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
+++ b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
@@ -426,7 +426,6 @@ System.CommandLine.Parsing
     public System.String ErrorMessage { get; set; }
     public System.CommandLine.LocalizationResources LocalizationResources { get; }
     public SymbolResult Parent { get; }
-    public System.CommandLine.Symbol Symbol { get; }
     public System.Collections.Generic.IReadOnlyList<Token> Tokens { get; }
     public ArgumentResult FindResultFor(System.CommandLine.Argument argument)
     public CommandResult FindResultFor(System.CommandLine.Command command)
diff --git a/src/System.CommandLine.Tests/ArgumentTests.cs b/src/System.CommandLine.Tests/ArgumentTests.cs
index bd4db062ee..937c6d4505 100644
--- a/src/System.CommandLine.Tests/ArgumentTests.cs
+++ b/src/System.CommandLine.Tests/ArgumentTests.cs
@@ -131,7 +131,7 @@ public void Validation_failure_message_can_be_specified_when_parsing_tokens()
                 argument.Parse("x")
                         .Errors
                         .Should()
-                        .ContainSingle(e => e.SymbolResult.Symbol == argument)
+                        .ContainSingle(e => ((ArgumentResult)e.SymbolResult).Argument == argument)
                         .Which
                         .Message
                         .Should()
@@ -150,7 +150,7 @@ public void Validation_failure_message_can_be_specified_when_evaluating_default_
                 argument.Parse("")
                         .Errors
                         .Should()
-                        .ContainSingle(e => e.SymbolResult.Symbol == argument)
+                        .ContainSingle(e => ((ArgumentResult)e.SymbolResult).Argument == argument)
                         .Which
                         .Message
                         .Should()
@@ -248,7 +248,10 @@ public void Option_ArgumentResult_Parent_is_set_correctly_when_token_is_implicit
 
                 argumentResult
                     .Parent
-                    .Symbol
+                    .Should()
+                    .BeOfType<OptionResult>()
+                    .Which
+                    .Option
                     .Should()
                     .Be(command.Options.Single());
             }
@@ -274,9 +277,12 @@ public void Option_ArgumentResult_parentage_to_root_symbol_is_set_correctly_when
                 argumentResult
                     .Parent
                     .Parent
-                    .Symbol
                     .Should()
-                    .Be(command);
+                    .BeAssignableTo<CommandResult>()
+                    .Which
+                    .Command
+                    .Should()
+                    .BeSameAs(command);
             }
             
             [Theory]
@@ -333,9 +339,12 @@ public void Command_ArgumentResult_Parent_is_set_correctly_when_token_is_implici
 
                 argumentResult
                     .Parent
-                    .Symbol
                     .Should()
-                    .Be(command);
+                    .BeAssignableTo<CommandResult>()
+                    .Which
+                    .Command
+                    .Should()
+                    .BeSameAs(command);
             }
 
             [Fact]
diff --git a/src/System.CommandLine.Tests/CommandTests.cs b/src/System.CommandLine.Tests/CommandTests.cs
index 6cb58c8d40..e40bb071f8 100644
--- a/src/System.CommandLine.Tests/CommandTests.cs
+++ b/src/System.CommandLine.Tests/CommandTests.cs
@@ -31,7 +31,7 @@ public void Outer_command_is_identified_correctly_by_RootCommand()
 
             result
                 .RootCommandResult
-                .Symbol
+                .Command
                 .Name
                 .Should()
                 .Be("outer");
@@ -45,7 +45,10 @@ public void Outer_command_is_identified_correctly_by_Parent_property()
             result
                 .CommandResult
                 .Parent
-                .Symbol
+                .Should()
+                .BeAssignableTo<CommandResult>()
+                .Which
+                .Command
                 .Name
                 .Should()
                 .Be("outer");
@@ -57,7 +60,10 @@ public void Inner_command_is_identified_correctly()
             var result = _parser.Parse("outer inner --option argument1");
 
             result.CommandResult
-                  .Symbol
+                  .Should()
+                  .BeOfType<CommandResult>()
+                  .Which
+                  .Command
                   .Name
                   .Should()
                   .Be("inner");
@@ -71,7 +77,10 @@ public void Inner_command_option_is_identified_correctly()
             result.CommandResult
                   .Children
                   .ElementAt(0)
-                  .Symbol
+                  .Should()
+                  .BeOfType<OptionResult>()
+                  .Which
+                  .Option
                   .Name
                   .Should()
                   .Be("option");
@@ -195,7 +204,7 @@ public void ParseResult_Command_identifies_innermost_command(string input, strin
 
             var result = outer.Parse(input);
 
-            result.CommandResult.Symbol.Name.Should().Be(expectedCommand);
+            result.CommandResult.Command.Name.Should().Be(expectedCommand);
         }
 
         [Fact]
diff --git a/src/System.CommandLine.Tests/ParseResultTests.cs b/src/System.CommandLine.Tests/ParseResultTests.cs
index d8f622b630..c8d87b6df4 100644
--- a/src/System.CommandLine.Tests/ParseResultTests.cs
+++ b/src/System.CommandLine.Tests/ParseResultTests.cs
@@ -75,12 +75,12 @@ public void Command_will_not_accept_a_command_if_a_sibling_command_has_already_b
 
             var result = new Parser(command).Parse("outer inner-one inner-two");
 
-            result.CommandResult.Symbol.Name.Should().Be("inner-one");
+            result.CommandResult.Command.Name.Should().Be("inner-one");
             result.Errors.Count.Should().Be(1);
 
             var result2 = new Parser(command).Parse("outer inner-two inner-one");
 
-            result2.CommandResult.Symbol.Name.Should().Be("inner-two");
+            result2.CommandResult.Command.Name.Should().Be("inner-two");
             result2.Errors.Count.Should().Be(1);
         }
     }
diff --git a/src/System.CommandLine.Tests/ParserTests.MultiplePositions.cs b/src/System.CommandLine.Tests/ParserTests.MultiplePositions.cs
index 5d0652953f..a915c08b4c 100644
--- a/src/System.CommandLine.Tests/ParserTests.MultiplePositions.cs
+++ b/src/System.CommandLine.Tests/ParserTests.MultiplePositions.cs
@@ -1,6 +1,7 @@
 // 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.Parsing;
 using System.Linq;
 using FluentAssertions;
 using Xunit;
@@ -141,7 +142,15 @@ public void A_command_can_be_specified_in_more_than_one_position(
                 var result = outer.Parse(commandLine);
 
                 result.Errors.Should().BeEmpty();
-                result.CommandResult.Parent.Symbol.Name.Should().Be(expectedParent);
+                result.CommandResult
+                    .Parent
+                    .Should()
+                    .BeOfType<CommandResult>()
+                    .Which
+                    .Command
+                    .Name
+                    .Should()
+                    .Be(expectedParent);
             }
 
             [Fact]
diff --git a/src/System.CommandLine.Tests/ParserTests.cs b/src/System.CommandLine.Tests/ParserTests.cs
index 17a4f02301..0c039a6bb4 100644
--- a/src/System.CommandLine.Tests/ParserTests.cs
+++ b/src/System.CommandLine.Tests/ParserTests.cs
@@ -129,7 +129,7 @@ public void Option_short_forms_can_be_bundled()
 
             result.CommandResult
                   .Children
-                  .Select(o => o.Symbol.Name)
+                  .Select(o => ((OptionResult)o).Option.Name)
                   .Should()
                   .BeEquivalentTo("x", "y", "z");
         }
@@ -172,7 +172,7 @@ public void Option_long_forms_do_not_get_unbundled()
 
             result.CommandResult
                   .Children
-                  .Select(o => o.Symbol.Name)
+                  .Select(o => ((OptionResult)o).Option.Name)
                   .Should()
                   .BeEquivalentTo("xyz");
         }
@@ -427,13 +427,13 @@ public void Command_with_multiple_options_is_parsed_correctly()
                   .Children
                   .Should()
                   .ContainSingle(o =>
-                                     o.Symbol.Name == "inner1" &&
+                                     ((OptionResult)o).Option.Name == "inner1" &&
                                      o.Tokens.Single().Value == "argument1");
             result.CommandResult
                   .Children
                   .Should()
                   .ContainSingle(o =>
-                                     o.Symbol.Name == "inner2" &&
+                                     ((OptionResult)o).Option.Name == "inner2" &&
                                      o.Tokens.Single().Value == "argument2");
         }
 
@@ -669,11 +669,11 @@ public void When_options_with_the_same_name_are_defined_on_parent_and_child_comm
                   .Parent
                   .Children
                   .Should()
-                  .NotContain(o => o.Symbol.Name == "x");
+                  .AllBeAssignableTo<CommandResult>();
             result.CommandResult
                   .Children
                   .Should()
-                  .ContainSingle(o => o.Symbol.Name == "x");
+                  .ContainSingle(o => ((OptionResult)o).Option.Name == "x");
         }
 
         [Fact]
@@ -695,7 +695,7 @@ public void When_options_with_the_same_name_are_defined_on_parent_and_child_comm
                   .Parent
                   .Children
                   .Should()
-                  .ContainSingle(o => o.Symbol.Name == "x");
+                  .ContainSingle(o => o is OptionResult && ((OptionResult)o).Option.Name == "x");
         }
 
         [Fact]
@@ -1003,7 +1003,7 @@ public void Option_and_Command_can_have_the_same_alias()
                   .Parent
                   .Children
                   .Should()
-                  .Contain(c => c.Symbol == option);
+                  .Contain(o => ((OptionResult)o).Option == option);
         }
 
         [Fact]
@@ -1020,12 +1020,12 @@ public void Options_can_have_the_same_alias_differentiated_only_by_prefix()
 
             parser.Parse("-a").CommandResult
                   .Children
-                  .Select(s => s.Symbol)
+                  .Select(s => ((OptionResult)s).Option)
                   .Should()
                   .BeEquivalentTo(option1);
             parser.Parse("--a").CommandResult
                   .Children
-                  .Select(s => s.Symbol)
+                  .Select(s => ((OptionResult)s).Option)
                   .Should()
                   .BeEquivalentTo(option2);
         }
diff --git a/src/System.CommandLine.Tests/ParsingValidationTests.cs b/src/System.CommandLine.Tests/ParsingValidationTests.cs
index 913fcb057f..f0e7fba9a9 100644
--- a/src/System.CommandLine.Tests/ParsingValidationTests.cs
+++ b/src/System.CommandLine.Tests/ParsingValidationTests.cs
@@ -48,7 +48,7 @@ public void When_an_option_has_en_error_then_the_error_has_a_reference_to_the_op
             result.Errors
                   .Where(e => e.SymbolResult != null)
                   .Should()
-                  .Contain(e => e.SymbolResult.Symbol.Name == option.Name);
+                  .Contain(e => ((OptionResult)e.SymbolResult).Option.Name == option.Name);
         }
 
         [Fact] // https://github.com/dotnet/command-line-api/issues/1475
@@ -201,7 +201,7 @@ public void When_a_required_option_is_not_supplied_then_an_error_is_returned()
                   .Should()
                   .HaveCount(1)
                   .And
-                  .Contain(e => e.SymbolResult.Symbol == command)
+                  .Contain(e => ((CommandResult)e.SymbolResult).Command == command)
                   .Which
                   .Message
                   .Should()
@@ -225,7 +225,7 @@ public void When_a_required_option_has_multiple_aliases_the_error_message_uses_l
                   .Should()
                   .HaveCount(1)
                   .And
-                  .Contain(e => e.SymbolResult.Symbol == command)
+                  .Contain(e => ((CommandResult)e.SymbolResult).Command == command)
                   .Which
                   .Message
                   .Should()
@@ -308,8 +308,8 @@ public void A_custom_validator_can_be_added_to_a_command()
 
             command.Validators.Add(commandResult =>
             {
-                if (commandResult.Children.Any(sr => sr.Symbol is IdentifierSymbol id && id.HasAlias("--one")) &&
-                    commandResult.Children.Any(sr => sr.Symbol is IdentifierSymbol id && id.HasAlias("--two")))
+                if (commandResult.Children.Any(sr => ((OptionResult)sr).Option.HasAlias("--one")) &&
+                    commandResult.Children.Any(sr => ((OptionResult)sr).Option.HasAlias("--two")))
                 {
                     commandResult.ErrorMessage = "Options '--one' and '--two' cannot be used together.";
                 }
@@ -346,7 +346,7 @@ public void A_custom_validator_can_be_added_to_an_option()
                   .Should()
                   .HaveCount(1)
                   .And
-                  .Contain(e => e.SymbolResult.Symbol == option)
+                  .Contain(e => ((OptionResult)e.SymbolResult).Option == option)
                   .Which
                   .Message
                   .Should()
@@ -373,7 +373,7 @@ public void A_custom_validator_can_be_added_to_an_argument()
                   .Should()
                   .HaveCount(1)
                   .And
-                  .Contain(e => e.SymbolResult.Symbol == argument)
+                  .Contain(e => ((ArgumentResult)e.SymbolResult).Argument == argument)
                   .Which
                   .Message
                   .Should()
@@ -442,7 +442,7 @@ public void Validators_on_global_options_are_executed_when_invoking_a_subcommand
                   .Should()
                   .HaveCount(1)
                   .And
-                  .Contain(e => e.SymbolResult.Symbol == option)
+                  .Contain(e => ((OptionResult)e.SymbolResult).Option == option)
                   .Which
                   .Message
                   .Should()
@@ -575,7 +575,7 @@ public void LegalFilePathsOnly_rejects_command_arguments_containing_invalid_path
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol == command.Arguments.First() &&
+                      .Contain(e => ((ArgumentResult)e.SymbolResult).Argument == command.Arguments.First() &&
                                     e.Message == $"Character not allowed in a path: '{invalidCharacter}'.");
             }   
             
@@ -597,7 +597,7 @@ public void LegalFilePathsOnly_rejects_option_arguments_containing_invalid_path_
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "x" &&
+                      .Contain(e => ((OptionResult)e.SymbolResult).Option.Name == "x" &&
                                     e.Message == $"Character not allowed in a path: '{invalidCharacter}'.");
             }
 
@@ -660,7 +660,7 @@ public void LegalFileNamesOnly_rejects_command_arguments_containing_invalid_file
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol == command.Arguments.First() &&
+                      .Contain(e => ((ArgumentResult)e.SymbolResult).Argument == command.Arguments.First() &&
                                     e.Message == $"Character not allowed in a file name: '{invalidCharacter}'.");
             }
 
@@ -683,7 +683,7 @@ public void LegalFileNamesOnly_rejects_option_arguments_containing_invalid_file_
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "x" &&
+                      .Contain(e => ((OptionResult)e.SymbolResult).Option.Name == "x" &&
                                     e.Message == $"Character not allowed in a file name: '{invalidCharacter}'.");
             }
 
@@ -743,7 +743,7 @@ public void A_command_argument_can_be_invalid_based_on_file_existence()
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .Contain(e => ((ArgumentResult)e.SymbolResult).Argument.Name == "to" &&
                                     e.Message == $"File does not exist: '{path}'.");
             }
 
@@ -762,7 +762,7 @@ public void An_option_argument_can_be_invalid_based_on_file_existence()
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .Contain(e => ((OptionResult)e.SymbolResult).Option.Name == "to" &&
                                     e.Message == $"File does not exist: '{path}'.");
             }
 
@@ -781,7 +781,7 @@ public void A_command_argument_can_be_invalid_based_on_directory_existence()
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .Contain(e => ((ArgumentResult)e.SymbolResult).Argument.Name == "to" &&
                                     e.Message == $"Directory does not exist: '{path}'.");
             }
 
@@ -800,7 +800,7 @@ public void An_option_argument_can_be_invalid_based_on_directory_existence()
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .Contain(e => ((OptionResult)e.SymbolResult).Option.Name == "to" &&
                                     e.Message == $"Directory does not exist: '{path}'.");
             }
 
@@ -819,7 +819,7 @@ public void A_command_argument_can_be_invalid_based_on_file_or_directory_existen
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol == command.Arguments.First() &&
+                      .Contain(e => ((ArgumentResult)e.SymbolResult).Argument == command.Arguments.First() &&
                                     e.Message == $"File or directory does not exist: '{path}'.");
             }
 
@@ -838,7 +838,7 @@ public void An_option_argument_can_be_invalid_based_on_file_or_directory_existen
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .Contain(e => ((OptionResult)e.SymbolResult).Option.Name == "to" &&
                                     e.Message == $"File or directory does not exist: '{path}'.");
             }
 
@@ -857,7 +857,7 @@ public void A_command_argument_with_multiple_files_can_be_invalid_based_on_file_
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "to" && 
+                      .Contain(e => ((ArgumentResult)e.SymbolResult).Argument.Name == "to" && 
                                     e.Message == $"File does not exist: '{path}'.");
             }
             
@@ -876,7 +876,7 @@ public void An_option_argument_with_multiple_files_can_be_invalid_based_on_file_
                       .Should()
                       .HaveCount(1)
                       .And
-                      .Contain(e => e.SymbolResult.Symbol.Name == "to" && 
+                      .Contain(e => ((OptionResult)e.SymbolResult).Option.Name == "to" && 
                                     e.Message == $"File does not exist: '{path}'.");
             }
 
@@ -895,7 +895,7 @@ public void A_command_argument_with_multiple_directories_can_be_invalid_based_on
                       .Should()
                       .HaveCount(1)
                       .And
-                      .ContainSingle(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .ContainSingle(e => ((ArgumentResult)e.SymbolResult).Argument.Name == "to" &&
                                           e.Message == $"Directory does not exist: '{path}'.");
             }
 
@@ -914,7 +914,7 @@ public void An_option_argument_with_multiple_directories_can_be_invalid_based_on
                       .Should()
                       .HaveCount(1)
                       .And
-                      .ContainSingle(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .ContainSingle(e => ((OptionResult)e.SymbolResult).Option.Name == "to" &&
                                           e.Message == $"Directory does not exist: '{path}'.");
             }
 
@@ -935,7 +935,7 @@ public void A_command_argument_with_multiple_FileSystemInfos_can_be_invalid_base
 
                 result.Errors
                       .Should()
-                      .ContainSingle(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .ContainSingle(e => ((ArgumentResult)e.SymbolResult).Argument.Name == "to" &&
                                           e.Message == $"File or directory does not exist: '{path}'.");
             }
 
@@ -954,7 +954,7 @@ public void An_option_argument_with_multiple_FileSystemInfos_can_be_invalid_base
 
                 result.Errors
                       .Should()
-                      .ContainSingle(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .ContainSingle(e => ((OptionResult)e.SymbolResult).Option.Name == "to" &&
                                           e.Message == $"File or directory does not exist: '{path}'.");
             }
 
@@ -973,7 +973,7 @@ public void A_command_argument_with_multiple_FileSystemInfos_can_be_invalid_base
                       .Should()
                       .HaveCount(1)
                       .And
-                      .ContainSingle(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .ContainSingle(e => ((ArgumentResult)e.SymbolResult).Argument.Name == "to" &&
                                           e.Message == $"File or directory does not exist: '{path}'.");
             }
 
@@ -992,7 +992,7 @@ public void An_option_argument_with_multiple_FileSystemInfos_can_be_invalid_base
                       .Should()
                       .HaveCount(1)
                       .And
-                      .ContainSingle(e => e.SymbolResult.Symbol.Name == "to" &&
+                      .ContainSingle(e => ((OptionResult)e.SymbolResult).Option.Name == "to" &&
                                           e.Message == $"File or directory does not exist: '{path}'.");
             }
 
@@ -1083,7 +1083,7 @@ public void A_command_with_subcommands_is_invalid_to_invoke_if_it_has_no_handler
                   .Should()
                   .ContainSingle(
                       e => e.Message.Equals(LocalizationResources.Instance.RequiredCommandWasNotProvided()) &&
-                           e.SymbolResult.Symbol.Name.Equals("inner"));
+                           ((CommandResult)e.SymbolResult).Command.Name.Equals("inner"));
         }
 
         [Fact]
@@ -1099,7 +1099,7 @@ public void A_root_command_is_invalid_if_it_has_no_handler()
                   .Should()
                   .ContainSingle(
                       e => e.Message.Equals(LocalizationResources.Instance.RequiredCommandWasNotProvided()) &&
-                           e.SymbolResult.Symbol == rootCommand);
+                           ((CommandResult)e.SymbolResult).Command == rootCommand);
         }
 
         [Fact]
diff --git a/src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs b/src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs
index 29ac9fef5e..54039b04bb 100644
--- a/src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs
+++ b/src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs
@@ -647,7 +647,7 @@ public static CommandLineBuilder UseVersionOption(
             {
                 if (context.ParseResult.FindResultFor(versionOption) is { })
                 {
-                    if (context.ParseResult.Errors.Any(e => e.SymbolResult?.Symbol is VersionOption))
+                    if (context.ParseResult.Errors.Any(e => e.SymbolResult is OptionResult optionResult && optionResult.Option is VersionOption))
                     {
                         context.InvocationResult = static ctx => ParseErrorResult.Apply(ctx, null);
                     }
@@ -688,7 +688,7 @@ public static CommandLineBuilder UseVersionOption(
             {
                 if (context.ParseResult.FindResultFor(versionOption) is { })
                 {
-                    if (context.ParseResult.Errors.Any(e => e.SymbolResult?.Symbol is VersionOption))
+                    if (context.ParseResult.Errors.Any(e => e.SymbolResult is OptionResult optionResult && optionResult.Option is VersionOption))
                     {
                         context.InvocationResult = static ctx => ParseErrorResult.Apply(ctx, null);
                     }
diff --git a/src/System.CommandLine/Help/VersionOption.cs b/src/System.CommandLine/Help/VersionOption.cs
index 800cbfb12e..70dd04639f 100644
--- a/src/System.CommandLine/Help/VersionOption.cs
+++ b/src/System.CommandLine/Help/VersionOption.cs
@@ -31,13 +31,13 @@ public VersionOption(string[] aliases, CommandLineBuilder builder) : base(aliase
 
         private void AddValidators()
         {
-            Validators.Add(result =>
+            Validators.Add(static result =>
             {
                 if (result.Parent is { } parent &&
-                    parent.Children.Where(r => r.Symbol is not VersionOption)
+                    parent.Children.Where(r => !(r is OptionResult optionResult && optionResult.Option is VersionOption))
                           .Any(IsNotImplicit))
                 {
-                    result.ErrorMessage =  result.LocalizationResources.VersionOptionCannotBeCombinedWithOtherArguments(result.Token?.Value ?? result.Symbol.Name);
+                    result.ErrorMessage =  result.LocalizationResources.VersionOptionCannotBeCombinedWithOtherArguments(result.Token?.Value);
                 }
             });
         }
diff --git a/src/System.CommandLine/ParseResult.cs b/src/System.CommandLine/ParseResult.cs
index b34f2ffb22..1616690e49 100644
--- a/src/System.CommandLine/ParseResult.cs
+++ b/src/System.CommandLine/ParseResult.cs
@@ -207,9 +207,14 @@ public T GetValue<T>(Argument<T> argument)
         public IEnumerable<CompletionItem> GetCompletions(
             int? position = null)
         {
-            var currentSymbolResult = SymbolToComplete(position);
+            SymbolResult currentSymbolResult = SymbolToComplete(position);
 
-            var currentSymbol = currentSymbolResult.Symbol;
+            Symbol currentSymbol = currentSymbolResult switch
+            {
+                ArgumentResult argumentResult => argumentResult.Argument,
+                OptionResult optionResult => optionResult.Option,
+                _ => ((CommandResult)currentSymbolResult).Command
+            };
 
             var context = GetCompletionContext();
 
diff --git a/src/System.CommandLine/Parsing/ArgumentResult.cs b/src/System.CommandLine/Parsing/ArgumentResult.cs
index 0b8450eaf7..949b9eba72 100644
--- a/src/System.CommandLine/Parsing/ArgumentResult.cs
+++ b/src/System.CommandLine/Parsing/ArgumentResult.cs
@@ -16,9 +16,9 @@ public sealed class ArgumentResult : SymbolResult
 
         internal ArgumentResult(
             Argument argument,
-            SymbolResult? parent) : base(argument, parent)
+            SymbolResult? parent) : base(parent)
         {
-            Argument = argument;
+            Argument = argument ?? throw new ArgumentNullException(nameof(argument));
         }
 
         /// <summary>
@@ -26,6 +26,8 @@ internal ArgumentResult(
         /// </summary>
         public Argument Argument { get; }
 
+        internal override int MaximumArgumentCapacity => Argument.Arity.MaximumNumberOfValues;
+
         internal bool IsImplicit => Argument.HasDefaultValue && Tokens.Count == 0;
 
         internal IReadOnlyList<Token>? PassedOnTokens { get; private set; }
diff --git a/src/System.CommandLine/Parsing/CommandResult.cs b/src/System.CommandLine/Parsing/CommandResult.cs
index 0c341b9fb9..56d22b2b07 100644
--- a/src/System.CommandLine/Parsing/CommandResult.cs
+++ b/src/System.CommandLine/Parsing/CommandResult.cs
@@ -16,10 +16,9 @@ internal CommandResult(
             Command command,
             Token token,
             CommandResult? parent = null) :
-            base(command ?? throw new ArgumentNullException(nameof(command)),
-                 parent)
+            base(parent)
         {
-            Command = command;
+            Command = command ?? throw new ArgumentNullException(nameof(command));
             Token = token ?? throw new ArgumentNullException(nameof(token));
         }
 
@@ -33,6 +32,26 @@ internal CommandResult(
         /// </summary>
         public Token Token { get; }
 
+        internal sealed override int MaximumArgumentCapacity
+        {
+            get
+            {
+                var value = 0;
+
+                if (Command.HasArguments)
+                {
+                    var arguments = Command.Arguments;
+
+                    for (var i = 0; i < arguments.Count; i++)
+                    {
+                        value += arguments[i].Arity.MaximumNumberOfValues;
+                    }
+                }
+
+                return value;
+            }
+        }
+
         internal override bool UseDefaultValueFor(Argument argument) =>
             FindResultFor(argument) switch
             {
diff --git a/src/System.CommandLine/Parsing/OptionResult.cs b/src/System.CommandLine/Parsing/OptionResult.cs
index 38419b1b0c..87725424f0 100644
--- a/src/System.CommandLine/Parsing/OptionResult.cs
+++ b/src/System.CommandLine/Parsing/OptionResult.cs
@@ -19,10 +19,9 @@ internal OptionResult(
             Option option,
             Token? token = null,
             CommandResult? parent = null) :
-            base(option ?? throw new ArgumentNullException(nameof(option)),
-                 parent)
+            base(parent)
         {
-            Option = option;
+            Option = option ?? throw new ArgumentNullException(nameof(option));
             Token = token;
         }
 
@@ -42,6 +41,8 @@ internal OptionResult(
         /// </summary>
         public Token? Token { get; }
 
+        internal override int MaximumArgumentCapacity => Option.Argument.Arity.MaximumNumberOfValues;
+
         /// <inheritdoc cref="GetValueOrDefault{T}"/>
         public object? GetValueOrDefault() =>
             Option.ValueType == typeof(bool)
diff --git a/src/System.CommandLine/Parsing/SymbolResult.cs b/src/System.CommandLine/Parsing/SymbolResult.cs
index 367e28ad52..9e0c9f66dc 100644
--- a/src/System.CommandLine/Parsing/SymbolResult.cs
+++ b/src/System.CommandLine/Parsing/SymbolResult.cs
@@ -16,12 +16,8 @@ public abstract class SymbolResult
         private List<SymbolResult>? _children;
         private protected List<Token>? _tokens;
 
-        private protected SymbolResult(
-            Symbol symbol, 
-            SymbolResult? parent)
+        private protected SymbolResult(SymbolResult? parent)
         {
-            Symbol = symbol ?? throw new ArgumentNullException(nameof(symbol));
-
             Parent = parent;
         }
 
@@ -43,11 +39,6 @@ private protected SymbolResult(
         /// </summary>
         public SymbolResult? Parent { get; }
 
-        /// <summary>
-        /// The symbol to which the result applies.
-        /// </summary>
-        public Symbol Symbol { get; }
-
         /// <summary>
         /// The list of tokens associated with this symbol result during parsing.
         /// </summary>
@@ -58,38 +49,7 @@ private protected SymbolResult(
         private protected virtual int RemainingArgumentCapacity =>
             MaximumArgumentCapacity - Tokens.Count;
 
-        internal int MaximumArgumentCapacity
-        {
-            get
-            {
-                switch (Symbol)
-                {
-                    case Option option:
-                        return option.Argument.Arity.MaximumNumberOfValues;
-
-                    case Argument argument:
-                        return argument.Arity.MaximumNumberOfValues;
-
-                    case Command command:
-                        var value = 0;
-
-                        if (command.HasArguments)
-                        {
-                            var arguments = command.Arguments;
-
-                            for (var i = 0; i < arguments.Count; i++)
-                            {
-                                value += arguments[i].Arity.MaximumNumberOfValues;
-                            }
-                        }
-
-                        return value;
-
-                    default:
-                        throw new NotSupportedException();
-                }
-            }
-        }
+        internal abstract int MaximumArgumentCapacity { get; }
 
         /// <summary>
         /// Localization resources used to produce messages for this symbol result.

From 5b57add6473746bbfac8fb64d3b6ba00f92c85c2 Mon Sep 17 00:00:00 2001
From: Adam Sitnik <adam.sitnik@gmail.com>
Date: Wed, 18 Jan 2023 13:34:13 +0100
Subject: [PATCH 3/5] not every SymbolResult can have children, move the
 property to derived types as well

---
 src/System.CommandLine/Help/VersionOption.cs       |  2 +-
 src/System.CommandLine/Parsing/CommandResult.cs    |  8 ++++++++
 src/System.CommandLine/Parsing/OptionResult.cs     | 14 ++++++--------
 .../Parsing/ParseResultVisitor.cs                  |  7 ++-----
 src/System.CommandLine/Parsing/SymbolResult.cs     |  8 --------
 5 files changed, 17 insertions(+), 22 deletions(-)

diff --git a/src/System.CommandLine/Help/VersionOption.cs b/src/System.CommandLine/Help/VersionOption.cs
index 70dd04639f..88153c2d64 100644
--- a/src/System.CommandLine/Help/VersionOption.cs
+++ b/src/System.CommandLine/Help/VersionOption.cs
@@ -33,7 +33,7 @@ private void AddValidators()
         {
             Validators.Add(static result =>
             {
-                if (result.Parent is { } parent &&
+                if (result.Parent is CommandResult parent &&
                     parent.Children.Where(r => !(r is OptionResult optionResult && optionResult.Option is VersionOption))
                           .Any(IsNotImplicit))
                 {
diff --git a/src/System.CommandLine/Parsing/CommandResult.cs b/src/System.CommandLine/Parsing/CommandResult.cs
index 56d22b2b07..0abaf2fa77 100644
--- a/src/System.CommandLine/Parsing/CommandResult.cs
+++ b/src/System.CommandLine/Parsing/CommandResult.cs
@@ -11,6 +11,7 @@ namespace System.CommandLine.Parsing
     public class CommandResult : SymbolResult
     {
         private Dictionary<Argument, ArgumentResult>? _defaultArgumentValues;
+        private List<SymbolResult>? _children;
 
         internal CommandResult(
             Command command,
@@ -32,6 +33,11 @@ internal CommandResult(
         /// </summary>
         public Token Token { get; }
 
+        /// <summary>
+        /// Child symbol results in the parse tree.
+        /// </summary>
+        public IReadOnlyList<SymbolResult> Children => _children is not null ? _children : Array.Empty<SymbolResult>();
+
         internal sealed override int MaximumArgumentCapacity
         {
             get
@@ -52,6 +58,8 @@ internal sealed override int MaximumArgumentCapacity
             }
         }
 
+        internal void AddChild(SymbolResult symbolResult) => (_children ??= new()).Add(symbolResult);
+
         internal override bool UseDefaultValueFor(Argument argument) =>
             FindResultFor(argument) switch
             {
diff --git a/src/System.CommandLine/Parsing/OptionResult.cs b/src/System.CommandLine/Parsing/OptionResult.cs
index 87725424f0..5ecb4dfb0f 100644
--- a/src/System.CommandLine/Parsing/OptionResult.cs
+++ b/src/System.CommandLine/Parsing/OptionResult.cs
@@ -12,6 +12,7 @@ namespace System.CommandLine.Parsing
     /// </summary>
     public sealed class OptionResult : SymbolResult
     {
+        private List<ArgumentResult>? _children;
         private ArgumentConversionResult? _argumentConversionResult;
         private Dictionary<Argument, ArgumentResult>? _defaultArgumentValues;
 
@@ -79,14 +80,9 @@ internal ArgumentConversionResult ArgumentConversionResult
             {
                 if (_argumentConversionResult is null)
                 {
-                    for (var i = 0; i < Children.Count; i++)
+                    if (_children is not null)
                     {
-                        var child = Children[i];
-
-                        if (child is ArgumentResult argumentResult)
-                        {
-                            return _argumentConversionResult = argumentResult.GetArgumentConversionResult();
-                        }
+                        return _argumentConversionResult = _children[0].GetArgumentConversionResult();
                     }
 
                     return _argumentConversionResult = ArgumentConversionResult.None(Option.Argument);
@@ -95,7 +91,9 @@ internal ArgumentConversionResult ArgumentConversionResult
                 return _argumentConversionResult;
             }
         }
-        
+
+        internal void AddChild(ArgumentResult argumentResult) => (_children ??= new()).Add(argumentResult);
+
         internal override bool UseDefaultValueFor(Argument argument) => IsImplicit;
 
         internal ArgumentResult GetOrCreateDefaultArgumentResult(Argument argument) =>
diff --git a/src/System.CommandLine/Parsing/ParseResultVisitor.cs b/src/System.CommandLine/Parsing/ParseResultVisitor.cs
index a5b52ed438..05d455deab 100644
--- a/src/System.CommandLine/Parsing/ParseResultVisitor.cs
+++ b/src/System.CommandLine/Parsing/ParseResultVisitor.cs
@@ -185,11 +185,8 @@ private void VisitOptionNode(OptionNode optionNode)
         private void VisitOptionArgumentNode(
             OptionArgumentNode argumentNode)
         {
-            _symbolResults.TryGetValue(
-                argumentNode.ParentOptionNode.Option,
-                out var optionResult);
-
-            if (optionResult is not OptionResult)
+            if (!(_symbolResults.TryGetValue(argumentNode.ParentOptionNode.Option, out SymbolResult? symbolResult)
+                    && symbolResult is OptionResult optionResult))
             {
                 return;
             }
diff --git a/src/System.CommandLine/Parsing/SymbolResult.cs b/src/System.CommandLine/Parsing/SymbolResult.cs
index 9e0c9f66dc..e2337c4563 100644
--- a/src/System.CommandLine/Parsing/SymbolResult.cs
+++ b/src/System.CommandLine/Parsing/SymbolResult.cs
@@ -13,7 +13,6 @@ namespace System.CommandLine.Parsing
     /// </summary>
     public abstract class SymbolResult
     {
-        private List<SymbolResult>? _children;
         private protected List<Token>? _tokens;
 
         private protected SymbolResult(SymbolResult? parent)
@@ -27,13 +26,6 @@ private protected SymbolResult(SymbolResult? parent)
         /// <remarks>Setting this value to a non-<c>null</c> during parsing will cause the parser to indicate an error for the user and prevent invocation of the command line.</remarks>
         public string? ErrorMessage { get; set; }
 
-        /// <summary>
-        /// Child symbol results in the parse tree.
-        /// </summary>
-        public IReadOnlyList<SymbolResult> Children => _children is not null ? _children : Array.Empty<SymbolResult>();
-
-        internal void AddChild(SymbolResult symbolResult) => (_children ??= new()).Add(symbolResult);
-
         /// <summary>
         /// The parent symbol result in the parse tree.
         /// </summary>

From ebd03955cd5ecb269c7f7839eb9b51a064345b01 Mon Sep 17 00:00:00 2001
From: Adam Sitnik <adam.sitnik@gmail.com>
Date: Wed, 18 Jan 2023 16:51:38 +0100
Subject: [PATCH 4/5] do not store the list of children per symbol result, use
 Parent property to find children using symbol dictionary

---
 ...ommandLine_api_is_not_changed.approved.txt |  2 +-
 src/System.CommandLine.Tests/ParserTests.cs   |  9 ++
 .../Parsing/CommandResult.cs                  | 12 +--
 .../Parsing/OptionResult.cs                   | 14 +--
 .../Parsing/ParseResultExtensions.cs          |  4 +-
 .../Parsing/ParseResultVisitor.cs             | 92 +++++++------------
 .../Parsing/RootCommandResult.cs              | 11 +++
 .../Parsing/SymbolResult.cs                   |  2 +
 .../Parsing/SymbolResultExtensions.cs         | 10 +-
 9 files changed, 64 insertions(+), 92 deletions(-)

diff --git a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
index d4fb931a66..452160cab6 100644
--- a/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
+++ b/src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt
@@ -393,6 +393,7 @@ System.CommandLine.Parsing
   public class CommandLineStringSplitter
     public System.Collections.Generic.IEnumerable<System.String> Split(System.String commandLine)
   public class CommandResult : SymbolResult
+    public System.Collections.Generic.IEnumerable<SymbolResult> Children { get; }
     public System.CommandLine.Command Command { get; }
     public Token Token { get; }
   public class OptionResult : SymbolResult
@@ -422,7 +423,6 @@ System.CommandLine.Parsing
     public static System.Threading.Tasks.Task<System.Int32> InvokeAsync(this Parser parser, System.String[] args, System.CommandLine.IConsole console = null, System.Threading.CancellationToken cancellationToken = null)
     public static System.CommandLine.ParseResult Parse(this Parser parser, System.String commandLine)
   public abstract class SymbolResult
-    public System.Collections.Generic.IReadOnlyList<SymbolResult> Children { get; }
     public System.String ErrorMessage { get; set; }
     public System.CommandLine.LocalizationResources LocalizationResources { get; }
     public SymbolResult Parent { get; }
diff --git a/src/System.CommandLine.Tests/ParserTests.cs b/src/System.CommandLine.Tests/ParserTests.cs
index 0c039a6bb4..6deae54c4c 100644
--- a/src/System.CommandLine.Tests/ParserTests.cs
+++ b/src/System.CommandLine.Tests/ParserTests.cs
@@ -667,6 +667,9 @@ public void When_options_with_the_same_name_are_defined_on_parent_and_child_comm
 
             result.CommandResult
                   .Parent
+                  .Should()
+                  .BeAssignableTo<CommandResult>()
+                  .Which
                   .Children
                   .Should()
                   .AllBeAssignableTo<CommandResult>();
@@ -693,6 +696,9 @@ public void When_options_with_the_same_name_are_defined_on_parent_and_child_comm
                   .BeEmpty();
             result.CommandResult
                   .Parent
+                  .Should()
+                  .BeAssignableTo<CommandResult>()
+                  .Which
                   .Children
                   .Should()
                   .ContainSingle(o => o is OptionResult && ((OptionResult)o).Option.Name == "x");
@@ -1001,6 +1007,9 @@ public void Option_and_Command_can_have_the_same_alias()
             parser.Parse("outer --inner inner")
                   .CommandResult
                   .Parent
+                  .Should()
+                  .BeAssignableTo<CommandResult>()
+                  .Which
                   .Children
                   .Should()
                   .Contain(o => ((OptionResult)o).Option == option);
diff --git a/src/System.CommandLine/Parsing/CommandResult.cs b/src/System.CommandLine/Parsing/CommandResult.cs
index 0abaf2fa77..dac4af0b37 100644
--- a/src/System.CommandLine/Parsing/CommandResult.cs
+++ b/src/System.CommandLine/Parsing/CommandResult.cs
@@ -10,9 +10,6 @@ namespace System.CommandLine.Parsing
     /// </summary>
     public class CommandResult : SymbolResult
     {
-        private Dictionary<Argument, ArgumentResult>? _defaultArgumentValues;
-        private List<SymbolResult>? _children;
-
         internal CommandResult(
             Command command,
             Token token,
@@ -36,7 +33,7 @@ internal CommandResult(
         /// <summary>
         /// Child symbol results in the parse tree.
         /// </summary>
-        public IReadOnlyList<SymbolResult> Children => _children is not null ? _children : Array.Empty<SymbolResult>();
+        public IEnumerable<SymbolResult> Children => GetChildren(this);
 
         internal sealed override int MaximumArgumentCapacity
         {
@@ -58,8 +55,6 @@ internal sealed override int MaximumArgumentCapacity
             }
         }
 
-        internal void AddChild(SymbolResult symbolResult) => (_children ??= new()).Add(symbolResult);
-
         internal override bool UseDefaultValueFor(Argument argument) =>
             FindResultFor(argument) switch
             {
@@ -67,10 +62,5 @@ internal override bool UseDefaultValueFor(Argument argument) =>
                                       arg.Tokens.Count == 0,
                 _ => false
             };
-
-        internal ArgumentResult GetOrCreateDefaultArgumentResult(Argument argument) =>
-            (_defaultArgumentValues ??= new()).GetOrAdd(
-                argument,
-                arg => new ArgumentResult(arg, this));
     }
 }
diff --git a/src/System.CommandLine/Parsing/OptionResult.cs b/src/System.CommandLine/Parsing/OptionResult.cs
index 5ecb4dfb0f..60d7dfb849 100644
--- a/src/System.CommandLine/Parsing/OptionResult.cs
+++ b/src/System.CommandLine/Parsing/OptionResult.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.Binding;
 using System.Diagnostics.CodeAnalysis;
 
@@ -12,9 +11,7 @@ namespace System.CommandLine.Parsing
     /// </summary>
     public sealed class OptionResult : SymbolResult
     {
-        private List<ArgumentResult>? _children;
         private ArgumentConversionResult? _argumentConversionResult;
-        private Dictionary<Argument, ArgumentResult>? _defaultArgumentValues;
 
         internal OptionResult(
             Option option,
@@ -80,9 +77,9 @@ internal ArgumentConversionResult ArgumentConversionResult
             {
                 if (_argumentConversionResult is null)
                 {
-                    if (_children is not null)
+                    if (FindResultFor(Option.Argument) is ArgumentResult firstChild)
                     {
-                        return _argumentConversionResult = _children[0].GetArgumentConversionResult();
+                        return _argumentConversionResult = firstChild.GetArgumentConversionResult();
                     }
 
                     return _argumentConversionResult = ArgumentConversionResult.None(Option.Argument);
@@ -92,13 +89,6 @@ internal ArgumentConversionResult ArgumentConversionResult
             }
         }
 
-        internal void AddChild(ArgumentResult argumentResult) => (_children ??= new()).Add(argumentResult);
-
         internal override bool UseDefaultValueFor(Argument argument) => IsImplicit;
-
-        internal ArgumentResult GetOrCreateDefaultArgumentResult(Argument argument) =>
-            (_defaultArgumentValues ??= new()).GetOrAdd(
-                argument,
-                arg => new ArgumentResult(arg, this));
     }
 }
diff --git a/src/System.CommandLine/Parsing/ParseResultExtensions.cs b/src/System.CommandLine/Parsing/ParseResultExtensions.cs
index f58592d802..e678e6b125 100644
--- a/src/System.CommandLine/Parsing/ParseResultExtensions.cs
+++ b/src/System.CommandLine/Parsing/ParseResultExtensions.cs
@@ -159,10 +159,8 @@ private static void Diagram(
                     builder.Append("[ ");
                     builder.Append(symbolResult.Token().Value);
 
-                    for (var i = 0; i < symbolResult.Children.Count; i++)
+                    foreach (SymbolResult child in symbolResult.GetChildren(symbolResult))
                     {
-                        var child = symbolResult.Children[i];
-
                         if (child is ArgumentResult arg &&
                             (arg.Argument.ValueType == typeof(bool) ||
                              arg.Argument.Arity.MaximumNumberOfValues == 0))
diff --git a/src/System.CommandLine/Parsing/ParseResultVisitor.cs b/src/System.CommandLine/Parsing/ParseResultVisitor.cs
index 05d455deab..a4b89e8bf0 100644
--- a/src/System.CommandLine/Parsing/ParseResultVisitor.cs
+++ b/src/System.CommandLine/Parsing/ParseResultVisitor.cs
@@ -95,21 +95,8 @@ private void VisitInternal(SyntaxNode node)
             }
         }
 
-        private void AddToResult(CommandResult result)
-        {
-            _innermostCommandResult?.AddChild(result);
-            _symbolResults.Add(result.Command, result);
-        }
-
-        private void AddToResult(OptionResult result)
-        {
-            _innermostCommandResult?.AddChild(result);
-            _symbolResults.TryAdd(result.Option, result);
-        }
-
         private void AddToResult(ArgumentResult result)
         {
-            _innermostCommandResult?.AddChild(result);
             if (_symbolResults.TryAdd(result.Argument, result))
             {
                 (_argumentResults ??= new()).Add(result);
@@ -134,16 +121,15 @@ private void VisitCommandNode(CommandNode commandNode)
                 commandNode.Token,
                 _innermostCommandResult);
 
-            AddToResult(commandResult);
+            _symbolResults.Add(commandNode.Command, commandResult);
 
             _innermostCommandResult = commandResult;
         }
 
         private void VisitCommandArgumentNode(CommandArgumentNode argumentNode)
         {
-            _symbolResults.TryGetValue(argumentNode.Argument, out var symbolResult);
-
-            if (symbolResult is not ArgumentResult argumentResult)
+            if (!(_symbolResults.TryGetValue(argumentNode.Argument, out var symbolResult)
+                    && symbolResult is ArgumentResult argumentResult))
             {
                 argumentResult =
                     new ArgumentResult(
@@ -164,9 +150,7 @@ private void VisitCommandArgumentNode(CommandArgumentNode argumentNode)
 
         private void VisitOptionNode(OptionNode optionNode)
         {
-            _symbolResults.TryGetValue(optionNode.Option, out var symbolResult);
-
-            if (symbolResult is not OptionResult)
+            if (!_symbolResults.ContainsKey(optionNode.Option))
             {
                 if (optionNode.Option is HelpOption)
                 {
@@ -178,28 +162,33 @@ private void VisitOptionNode(OptionNode optionNode)
                     optionNode.Token,
                     _innermostCommandResult);
 
-                AddToResult(optionResult);
+                _symbolResults.Add(optionNode.Option, optionResult);
+
+                if (optionNode.Children is null) // no Arguments
+                {
+                    if (optionResult.Option.Argument.HasCustomParser)
+                    {
+                        ArgumentResult argumentResult = new (optionResult.Option.Argument, optionResult);
+                        _symbolResults.Add(optionResult.Option.Argument, argumentResult);
+                    }
+                }
             }
         }
 
         private void VisitOptionArgumentNode(
             OptionArgumentNode argumentNode)
         {
-            if (!(_symbolResults.TryGetValue(argumentNode.ParentOptionNode.Option, out SymbolResult? symbolResult)
-                    && symbolResult is OptionResult optionResult))
-            {
-                return;
-            }
+            OptionResult optionResult = (OptionResult)_symbolResults[argumentNode.ParentOptionNode.Option];
 
             var argument = argumentNode.Argument;
 
-            if (!_symbolResults.TryGetValue(argument, out var argumentResult))
+            if (!(_symbolResults.TryGetValue(argument, out SymbolResult? symbolResult)
+                    && symbolResult is ArgumentResult argumentResult))
             {
                 argumentResult =
                     new ArgumentResult(
                         argumentNode.Argument,
                         optionResult);
-                optionResult.AddChild(argumentResult);
                 _symbolResults.TryAdd(argument, argumentResult);
             }
 
@@ -482,27 +471,11 @@ private void ValidateAndConvertOptionResult(OptionResult optionResult)
                 }
             }
 
-            if (optionResult.Children.Count == 0)
+            foreach (var pair in _symbolResults)
             {
-                if (optionResult.Option.Argument is { HasCustomParser: true })
+                if (object.ReferenceEquals(pair.Value.Parent, optionResult))
                 {
-                    if (optionResult.Option is { } opt)
-                    {
-                        var argResult = optionResult.GetOrCreateDefaultArgumentResult(opt.Argument);
-                        optionResult.AddChild(argResult);
-                        ValidateAndConvertArgumentResult(argResult);
-                    }
-                }
-            }
-            else
-            {
-                for (var i = 0; i < optionResult.Children.Count; i++)
-                {
-                    var result = optionResult.Children[i];
-                    if (result is ArgumentResult argumentResult)
-                    {
-                        ValidateAndConvertArgumentResult(argumentResult);
-                    }
+                    ValidateAndConvertArgumentResult((ArgumentResult)pair.Value);
                 }
             }
         }
@@ -576,11 +549,10 @@ void Handle(SymbolResult? symbolResult, Symbol symbol)
                 {
                     case OptionResult o:
 
-                        if (o.Children.Count == 0 &&
-                            o.Option.Argument.ValueType == typeof(bool))
+                        if (o.Option.Argument.ValueType == typeof(bool)
+                            && !_symbolResults.ContainsKey(o.Option.Argument))
                         {
-                            o.AddChild(
-                                new ArgumentResult(o.Option.Argument, o));
+                            _symbolResults.Add(o.Option.Argument, new ArgumentResult(o.Option.Argument, o));
                         }
 
                         break;
@@ -595,20 +567,20 @@ void Handle(SymbolResult? symbolResult, Symbol symbol)
                                     null,
                                     commandResult);
 
-                                var childArgumentResult = optionResult.GetOrCreateDefaultArgumentResult(
-                                    option.Argument);
-
-                                optionResult.AddChild(childArgumentResult);
-                                commandResult.AddChild(optionResult);
-                                _symbolResults.TryAdd(optionResult.Option, optionResult);
+                                if (_symbolResults.TryAdd(optionResult.Option, optionResult))
+                                {
+                                    _symbolResults.Add(optionResult.Option.Argument, new ArgumentResult(optionResult.Option.Argument, optionResult));
+                                }
 
                                 break;
 
                             case Argument { HasDefaultValue: true } argument:
 
-                                var argumentResult = commandResult.GetOrCreateDefaultArgumentResult(argument);
-
-                                AddToResult(argumentResult);
+                                if (!_symbolResults.ContainsKey(argument))
+                                {
+                                    AddToResult(new ArgumentResult(argument, commandResult));
+                                }
+                                
                                 break;
                         }
 
diff --git a/src/System.CommandLine/Parsing/RootCommandResult.cs b/src/System.CommandLine/Parsing/RootCommandResult.cs
index 680db15df5..f6c5461de8 100644
--- a/src/System.CommandLine/Parsing/RootCommandResult.cs
+++ b/src/System.CommandLine/Parsing/RootCommandResult.cs
@@ -30,5 +30,16 @@ public RootCommandResult(
 
         public override OptionResult? FindResultFor(Option option)
             => _symbolResults.TryGetValue(option, out SymbolResult? result) ? (OptionResult)result : default;
+
+        internal override IEnumerable<SymbolResult> GetChildren(SymbolResult parent)
+        {
+            foreach (var pair in _symbolResults)
+            {
+                if (ReferenceEquals(parent, pair.Value.Parent))
+                {
+                    yield return pair.Value;
+                }
+            }
+        }
     }
 }
diff --git a/src/System.CommandLine/Parsing/SymbolResult.cs b/src/System.CommandLine/Parsing/SymbolResult.cs
index e2337c4563..674c288523 100644
--- a/src/System.CommandLine/Parsing/SymbolResult.cs
+++ b/src/System.CommandLine/Parsing/SymbolResult.cs
@@ -71,6 +71,8 @@ private protected SymbolResult(SymbolResult? parent)
         /// <returns>An option result if the option was matched by the parser or has a default value; otherwise, <c>null</c>.</returns>
         public virtual OptionResult? FindResultFor(Option option) => GetRoot().FindResultFor(option);
 
+        internal virtual IEnumerable<SymbolResult> GetChildren(SymbolResult parent) => GetRoot().GetChildren(parent);
+
         private SymbolResult GetRoot()
         {
             SymbolResult result = this;
diff --git a/src/System.CommandLine/Parsing/SymbolResultExtensions.cs b/src/System.CommandLine/Parsing/SymbolResultExtensions.cs
index e447f37ada..443fdcfe62 100644
--- a/src/System.CommandLine/Parsing/SymbolResultExtensions.cs
+++ b/src/System.CommandLine/Parsing/SymbolResultExtensions.cs
@@ -7,13 +7,13 @@ namespace System.CommandLine.Parsing
 {
     internal static class SymbolResultExtensions
     {
-        internal static IEnumerable<SymbolResult> AllSymbolResults(this SymbolResult symbolResult)
+        internal static IEnumerable<SymbolResult> AllSymbolResults(this CommandResult commandResult)
         {
-            yield return symbolResult;
+            yield return commandResult;
 
-            foreach (var item in symbolResult
+            foreach (var item in commandResult
                                  .Children
-                                 .FlattenBreadthFirst(o => o.Children))
+                                 .FlattenBreadthFirst(o => o.GetChildren(o)))
             {
                 yield return item;
             }
@@ -28,7 +28,7 @@ internal static Token Token(this SymbolResult symbolResult)
                 _ => throw new ArgumentOutOfRangeException(nameof(symbolResult))
             };
 
-            Token CreateImplicitToken(Option option)
+            static Token CreateImplicitToken(Option option)
             {
                 return new Token(option.GetLongestAlias(removePrefix: false), TokenType.Option, option, Parsing.Token.ImplicitPosition);
             }

From a10c271225b47209ad91e5f61200c2ddd9be2d22 Mon Sep 17 00:00:00 2001
From: Adam Sitnik <adam.sitnik@gmail.com>
Date: Wed, 18 Jan 2023 20:38:21 +0100
Subject: [PATCH 5/5] fix the build ;)

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

diff --git a/src/System.CommandLine/Help/VersionOption.cs b/src/System.CommandLine/Help/VersionOption.cs
index 88153c2d64..55b4d9e9c0 100644
--- a/src/System.CommandLine/Help/VersionOption.cs
+++ b/src/System.CommandLine/Help/VersionOption.cs
@@ -37,7 +37,7 @@ private void AddValidators()
                     parent.Children.Where(r => !(r is OptionResult optionResult && optionResult.Option is VersionOption))
                           .Any(IsNotImplicit))
                 {
-                    result.ErrorMessage =  result.LocalizationResources.VersionOptionCannotBeCombinedWithOtherArguments(result.Token?.Value);
+                    result.ErrorMessage = result.LocalizationResources.VersionOptionCannotBeCombinedWithOtherArguments(result.Token?.Value ?? result.Option.Name);
                 }
             });
         }