More SymbolResult improvements (#2027)

* remove RootCommandResult (internal), introduce SymbolResultTree (internal) and make all virtual SymbolResult methods non-virtual and delegating to SymbolResultTree

* remove internal SymbolResult.GetChildren, expose SymbolResult.SymbolResultTree as internal field, optimize SymbolResultTree.GetChildren for AgumentResult

* make SymbolResultTree derive from Dictionary<Symbol, SymbolResult>

* it makes SymbolResultTree more responsible and less artificial (subjective)
* it removes one allocation (nit)

* update the token with missing information during parsing, so later stages don't need to modify it

* refactor the code so root command and inner most command are never nulls

Author: adamsitnik

src/System.CommandLine.Tests/ArgumentTests.cs

@@ -278,7 +278,7 @@ public void Option_ArgumentResult_parentage_to_root_symbol_is_set_correctly_when
                     .Parent
                     .Parent
                     .Should()
-                    .BeAssignableTo<CommandResult>()
+                    .BeOfType<CommandResult>()
                     .Which
                     .Command
                     .Should()
@@ -340,7 +340,7 @@ public void Command_ArgumentResult_Parent_is_set_correctly_when_token_is_implici
                 argumentResult
                     .Parent
                     .Should()
-                    .BeAssignableTo<CommandResult>()
+                    .BeOfType<CommandResult>()
                     .Which
                     .Command
                     .Should()

src/System.CommandLine.Tests/CommandTests.cs

@@ -46,7 +46,7 @@ public void Outer_command_is_identified_correctly_by_Parent_property()
                 .CommandResult
                 .Parent
                 .Should()
-                .BeAssignableTo<CommandResult>()
+                .BeOfType<CommandResult>()
                 .Which
                 .Command
                 .Name

src/System.CommandLine.Tests/ParserTests.cs

@@ -668,7 +668,7 @@ public void When_options_with_the_same_name_are_defined_on_parent_and_child_comm
             result.CommandResult
                   .Parent
                   .Should()
-                  .BeAssignableTo<CommandResult>()
+                  .BeOfType<CommandResult>()
                   .Which
                   .Children
                   .Should()
@@ -697,7 +697,7 @@ public void When_options_with_the_same_name_are_defined_on_parent_and_child_comm
             result.CommandResult
                   .Parent
                   .Should()
-                  .BeAssignableTo<CommandResult>()
+                  .BeOfType<CommandResult>()
                   .Which
                   .Children
                   .Should()
@@ -1008,7 +1008,7 @@ public void Option_and_Command_can_have_the_same_alias()
                   .CommandResult
                   .Parent
                   .Should()
-                  .BeAssignableTo<CommandResult>()
+                  .BeOfType<CommandResult>()
                   .Which
                   .Children
                   .Should()

src/System.CommandLine/Argument.cs

@@ -113,7 +113,7 @@ private protected override string DefaultName
         /// <returns>Returns the default value for the argument, if defined. Null otherwise.</returns>
         public object? GetDefaultValue()
         {
-            return GetDefaultValue(new ArgumentResult(this, null));
+            return GetDefaultValue(new ArgumentResult(this, null!, null));
         }
 
         internal abstract object? GetDefaultValue(ArgumentResult argumentResult);

src/System.CommandLine/ParseResult.cs

@@ -15,14 +15,14 @@ namespace System.CommandLine
     public class ParseResult
     {
         private readonly IReadOnlyList<ParseError> _errors;
-        private readonly RootCommandResult _rootCommandResult;
+        private readonly CommandResult _rootCommandResult;
         private readonly IReadOnlyList<Token> _unmatchedTokens;
         private Dictionary<string, IReadOnlyList<string>>? _directives;
         private CompletionContext? _completionContext;
 
         internal ParseResult(
             Parser parser,
-            RootCommandResult rootCommandResult,
+            CommandResult rootCommandResult,
             CommandResult commandResult,
             Dictionary<string, IReadOnlyList<string>>? directives,
             List<Token> tokens,

src/System.CommandLine/Parsing/ArgumentResult.cs

@@ -16,7 +16,8 @@ public sealed class ArgumentResult : SymbolResult
 
         internal ArgumentResult(
             Argument argument,
-            SymbolResult? parent) : base(parent)
+            SymbolResultTree symbolResultTree,
+            SymbolResult? parent) : base(symbolResultTree, parent)
         {
             Argument = argument ?? throw new ArgumentNullException(nameof(argument));
         }
@@ -110,7 +111,7 @@ Parent is { } &&
 
             if (Parent!.UseDefaultValueFor(argument))
             {
-                var argumentResult = new ArgumentResult(argument, Parent);
+                var argumentResult = new ArgumentResult(argument, SymbolResultTree, Parent);
 
                 var defaultValue = argument.GetDefaultValue(argumentResult);
 

src/System.CommandLine/Parsing/CommandResult.cs

@@ -8,13 +8,14 @@ namespace System.CommandLine.Parsing
     /// <summary>
     /// A result produced when parsing a <see cref="Command" />.
     /// </summary>
-    public class CommandResult : SymbolResult
+    public sealed class CommandResult : SymbolResult
     {
         internal CommandResult(
             Command command,
             Token token,
+            SymbolResultTree symbolResultTree,
             CommandResult? parent = null) :
-            base(parent)
+            base(symbolResultTree, parent)
         {
             Command = command ?? throw new ArgumentNullException(nameof(command));
             Token = token ?? throw new ArgumentNullException(nameof(token));
@@ -33,7 +34,7 @@ internal CommandResult(
         /// <summary>
         /// Child symbol results in the parse tree.
         /// </summary>
-        public IEnumerable<SymbolResult> Children => GetChildren(this);
+        public IEnumerable<SymbolResult> Children => SymbolResultTree.GetChildren(this);
 
         internal sealed override int MaximumArgumentCapacity
         {

src/System.CommandLine/Parsing/OptionResult.cs

@@ -15,9 +15,10 @@ public sealed class OptionResult : SymbolResult
 
         internal OptionResult(
             Option option,
+            SymbolResultTree symbolResultTree,
             Token? token = null,
             CommandResult? parent = null) :
-            base(parent)
+            base(symbolResultTree, parent)
         {
             Option = option ?? throw new ArgumentNullException(nameof(option));
             Token = token;

src/System.CommandLine/Parsing/ParseOperation.cs

@@ -102,6 +102,12 @@ private void ParseCommandArguments(CommandNode commandNode, ref int currentArgum
 
                     if (currentArgumentCount < argument.Arity.MaximumNumberOfValues)
                     {
+                        if (CurrentToken.Symbol is null)
+                        {
+                            // update the token with missing information now, so later stages don't need to modify it
+                            CurrentToken.Symbol = argument;
+                        }
+
                         var argumentNode = new CommandArgumentNode(
                             CurrentToken,
                             argument,

src/System.CommandLine/Parsing/ParseResultExtensions.cs

@@ -159,7 +159,7 @@ private static void Diagram(
                     builder.Append("[ ");
                     builder.Append(symbolResult.Token().Value);
 
-                    foreach (SymbolResult child in symbolResult.GetChildren(symbolResult))
+                    foreach (SymbolResult child in symbolResult.SymbolResultTree.GetChildren(symbolResult))
                     {
                         if (child is ArgumentResult arg &&
                             (arg.Argument.ValueType == typeof(bool) ||