Replace ValidateSymbolResult delegate with Action<T>, fixes #1944

src/System.CommandLine.ApiCompatibility.Tests/ApiCompatibilityApprovalTests.System_CommandLine_api_is_not_changed.approved.txt

@@ -5,7 +5,7 @@ System.CommandLine
     public System.Boolean HasDefaultValue { get; }
     public System.String HelpName { get; set; }
     public System.Type ValueType { get; }
-    public System.Void AddValidator(System.CommandLine.Parsing.ValidateSymbolResult<System.CommandLine.Parsing.ArgumentResult> validate)
+    public System.Void AddValidator(System.Action<System.CommandLine.Parsing.ArgumentResult> validate)
     public System.Collections.Generic.IEnumerable<System.CommandLine.Completions.CompletionItem> GetCompletions(System.CommandLine.Completions.CompletionContext context)
     public System.Object GetDefaultValue()
     public System.Void SetDefaultValue(System.Object value)
@@ -60,7 +60,7 @@ System.CommandLine
     public System.Void AddCommand(Command command)
     public System.Void AddGlobalOption(Option option)
     public System.Void AddOption(Option option)
-    public System.Void AddValidator(System.CommandLine.Parsing.ValidateSymbolResult<System.CommandLine.Parsing.CommandResult> validate)
+    public System.Void AddValidator(System.Action<System.CommandLine.Parsing.CommandResult> validate)
     public System.Collections.Generic.IEnumerable<System.CommandLine.Completions.CompletionItem> GetCompletions(System.CommandLine.Completions.CompletionContext context)
     public System.Collections.Generic.IEnumerator<Symbol> GetEnumerator()
   public static class CommandExtensions
@@ -194,7 +194,7 @@ System.CommandLine
     public ArgumentArity Arity { get; set; }
     public System.Boolean IsRequired { get; set; }
     public System.Type ValueType { get; }
-    public System.Void AddValidator(System.CommandLine.Parsing.ValidateSymbolResult<System.CommandLine.Parsing.OptionResult> validate)
+    public System.Void AddValidator(System.Action<System.CommandLine.Parsing.OptionResult> validate)
     public System.Collections.Generic.IEnumerable<System.CommandLine.Completions.CompletionItem> GetCompletions(System.CommandLine.Completions.CompletionContext context)
     public System.Boolean HasAliasIgnoringPrefix(System.String alias)
     public System.Void SetDefaultValue(System.Object value)
@@ -474,8 +474,3 @@ System.CommandLine.Parsing
     public System.IAsyncResult BeginInvoke(System.String tokenToReplace, ref System.Collections.Generic.IReadOnlyList<System.String> replacementTokens, ref System.String& errorMessage, System.AsyncCallback callback, System.Object object)
     public System.Boolean EndInvoke(ref System.Collections.Generic.IReadOnlyList<System.String> replacementTokens, ref System.String& errorMessage, System.IAsyncResult result)
     public System.Boolean Invoke(System.String tokenToReplace, ref System.Collections.Generic.IReadOnlyList<System.String> replacementTokens, ref System.String& errorMessage)
-  public delegate ValidateSymbolResult<in T> : System.MulticastDelegate, System.ICloneable, System.Runtime.Serialization.ISerializable
-    .ctor(System.Object object, System.IntPtr method)
-    public System.IAsyncResult BeginInvoke(T symbolResult, System.AsyncCallback callback, System.Object object)
-    public System.Void EndInvoke(System.IAsyncResult result)
-    public System.Void Invoke(T symbolResult)

src/System.CommandLine/Argument.cs

@@ -18,7 +18,7 @@ public abstract class Argument : Symbol, IValueDescriptor
         private ArgumentArity _arity;
         private TryConvertArgument? _convertArguments;
         private List<ICompletionSource>? _completions = null;
-        private List<ValidateSymbolResult<ArgumentResult>>? _validators = null;
+        private List<Action<ArgumentResult>>? _validators = null;
 
         /// <summary>
         /// Initializes a new instance of the Argument class.
@@ -104,14 +104,14 @@ private protected override string DefaultName
             }
         }
 
-        internal List<ValidateSymbolResult<ArgumentResult>> Validators => _validators ??= new ();
+        internal List<Action<ArgumentResult>> Validators => _validators ??= new ();
 
         /// <summary>
-        /// Adds a custom <see cref="ValidateSymbolResult{ArgumentResult}"/> to the argument. Validators can be used
+        /// Adds a custom validator to the argument. Validators can be used
         /// to provide custom errors based on user input.
         /// </summary>
-        /// <param name="validate">The delegate to validate the parsed argument.</param>
-        public void AddValidator(ValidateSymbolResult<ArgumentResult> validate) => Validators.Add(validate);
+        /// <param name="validate">The action to validate the parsed argument.</param>
+        public void AddValidator(Action<ArgumentResult> validate) => Validators.Add(validate);
 
         /// <summary>
         /// Gets the default value for the argument.

src/System.CommandLine/Command.cs

@@ -22,7 +22,7 @@ public class Command : IdentifierSymbol, IEnumerable<Symbol>
         private List<Argument>? _arguments;
         private List<Option>? _options;
         private List<Command>? _subcommands;
-        private List<ValidateSymbolResult<CommandResult>>? _validators;
+        private List<Action<CommandResult>>? _validators;
 
         /// <summary>
         /// Initializes a new instance of the Command class.
@@ -68,8 +68,8 @@ public IEnumerable<Symbol> Children
         /// </summary>
         public IReadOnlyList<Command> Subcommands => _subcommands is not null ? _subcommands : Array.Empty<Command>();
 
-        internal IReadOnlyList<ValidateSymbolResult<CommandResult>> Validators
-            => _validators is not null ? _validators : Array.Empty<ValidateSymbolResult<CommandResult>>();
+        internal IReadOnlyList<Action<CommandResult>> Validators
+            => _validators is not null ? _validators : Array.Empty<Action<CommandResult>>();
 
         internal bool HasValidators => _validators is not null; // initialized by Add method, so when it's not null the Count is always > 0
 
@@ -140,8 +140,8 @@ public void AddGlobalOption(Option option)
         /// Adds a custom validator to the command. Validators can be used
         /// to create custom validation logic.
         /// </summary>
-        /// <param name="validate">The delegate to validate the symbols during parsing.</param>
-        public void AddValidator(ValidateSymbolResult<CommandResult> validate) => (_validators ??= new()).Add(validate);
+        /// <param name="validate">The action to validate the symbols during parsing.</param>
+        public void AddValidator(Action<CommandResult> validate) => (_validators ??= new()).Add(validate);
 
         /// <summary>
         /// Gets or sets a value that indicates whether unmatched tokens should be treated as errors. For example,

src/System.CommandLine/Option.cs

@@ -16,7 +16,7 @@ namespace System.CommandLine
     public abstract class Option : IdentifierSymbol, IValueDescriptor
     {
         private string? _name;
-        private List<ValidateSymbolResult<OptionResult>>? _validators;
+        private List<Action<OptionResult>>? _validators;
         private readonly Argument _argument;
 
         internal Option(
@@ -112,15 +112,15 @@ public override string Name
             }
         }
 
-        internal List<ValidateSymbolResult<OptionResult>> Validators => _validators ??= new();
+        internal List<Action<OptionResult>> Validators => _validators ??= new();
 
         internal bool HasValidators => _validators is not null && _validators.Count > 0;
 
         /// <summary>
         /// Adds a validator that will be called when the option is matched by the parser.
         /// </summary>
-        /// <param name="validate">A <see cref="ValidateSymbolResult{OptionResult}"/> delegate used to validate the <see cref="OptionResult"/> produced during parsing.</param>
-        public void AddValidator(ValidateSymbolResult<OptionResult> validate) => Validators.Add(validate);
+        /// <param name="validate">An action used to validate the <see cref="OptionResult"/> produced during parsing.</param>
+        public void AddValidator(Action<OptionResult> validate) => Validators.Add(validate);
 
         /// <summary>
         /// Indicates whether a given alias exists on the option, regardless of its prefix.