make AddValidator fluent

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

@@ -5,7 +5,6 @@ System.CommandLine
     public System.Boolean HasDefaultValue { get; }
     public System.String HelpName { get; set; }
     public System.Type ValueType { get; }
-    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 ParseResult Parse(System.String commandLine)
@@ -28,6 +27,7 @@ System.CommandLine
     public Argument<T> AddCompletions(System.String[] completions)
     public Argument<T> AddCompletions(System.Func<System.CommandLine.Completions.CompletionContext,System.Collections.Generic.IEnumerable<System.String>> completionsDelegate)
     public Argument<T> AddCompletions(System.Func<System.CommandLine.Completions.CompletionContext,System.Collections.Generic.IEnumerable<System.CommandLine.Completions.CompletionItem>> completionsDelegate)
+    public Argument<T> AddValidator(System.Action<System.CommandLine.Parsing.ArgumentResult> validate)
   public struct ArgumentArity : System.ValueType, System.IEquatable<ArgumentArity>
     public static ArgumentArity ExactlyOne { get; }
     public static ArgumentArity OneOrMore { get; }
@@ -193,7 +193,6 @@ System.CommandLine
     public ArgumentArity Arity { get; set; }
     public System.Boolean IsRequired { get; set; }
     public System.Type ValueType { get; }
-    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 ParseResult Parse(System.String commandLine)
@@ -213,6 +212,7 @@ System.CommandLine
     public Option<T> AddCompletions(System.String[] completions)
     public Option<T> AddCompletions(System.Func<System.CommandLine.Completions.CompletionContext,System.Collections.Generic.IEnumerable<System.String>> completionsDelegate)
     public Option<T> AddCompletions(System.Func<System.CommandLine.Completions.CompletionContext,System.Collections.Generic.IEnumerable<System.CommandLine.Completions.CompletionItem>> completionsDelegate)
+    public Option<T> AddValidator(System.Action<System.CommandLine.Parsing.OptionResult> validate)
   public static class OptionValidation
     public static Option<System.IO.FileInfo> AcceptExistingOnly(this Option<System.IO.FileInfo> option)
     public static Option<System.IO.DirectoryInfo> AcceptExistingOnly(this Option<System.IO.DirectoryInfo> option)

src/System.CommandLine.Tests/ArgumentTests.cs

@@ -792,6 +792,7 @@ public void Argument_of_T_fluent_APIs_return_Argument_of_T()
                 .AddCompletions("test")
                 .AddCompletions(ctx => Array.Empty<string>())
                 .AddCompletions(ctx => Array.Empty<CompletionItem>())
+                .AddValidator(_ => { })
                 .AcceptLegalFileNamesOnly()
                 .AcceptLegalFilePathsOnly();
 

src/System.CommandLine.Tests/OptionTests.cs

@@ -394,6 +394,7 @@ public void Option_of_T_fluent_APIs_return_Option_of_T()
                 .AddCompletions("test")
                 .AddCompletions(ctx => Array.Empty<string>())
                 .AddCompletions(ctx => Array.Empty<CompletionItem>())
+                .AddValidator(_ => { })
                 .AcceptLegalFileNamesOnly()
                 .AcceptLegalFilePathsOnly();
 

src/System.CommandLine/Argument.cs

@@ -106,13 +106,6 @@ private protected override string DefaultName
 
         internal List<Action<ArgumentResult>> Validators => _validators ??= new ();
 
-        /// <summary>
-        /// Adds a custom validator to the argument. Validators can be used
-        /// to provide custom errors based on user input.
-        /// </summary>
-        /// <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.
         /// </summary>

src/System.CommandLine/Argument{T}.cs

@@ -153,6 +153,17 @@ public Argument<T> AddCompletions(Func<CompletionContext, IEnumerable<Completion
             return this;
         }
 
+        /// <summary>
+        /// Adds a custom validator to the argument. Validators can be used
+        /// to provide custom errors based on user input.
+        /// </summary>
+        /// <param name="validate">The action to validate the parsed argument.</param>
+        public Argument<T> AddValidator(Action<ArgumentResult> validate)
+        {
+            Validators.Add(validate);
+            return this;
+        }
+
         /// <summary>
         /// Configures the argument to accept only the specified values, and to suggest them as command line completions.
         /// </summary>

src/System.CommandLine/Option.cs

@@ -101,12 +101,6 @@ public override string Name
 
         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">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.
         /// </summary>

src/System.CommandLine/OptionValidation.cs

@@ -18,7 +18,7 @@ public static class OptionValidation
         /// <returns>The option being extended.</returns>
         public static Option<FileInfo> AcceptExistingOnly(this Option<FileInfo> option)
         {
-            option.Argument.AddValidator(Validate.FileExists);
+            option.Argument.Validators.Add(Validate.FileExists);
             return option;
         }
 
@@ -29,7 +29,7 @@ public static Option<FileInfo> AcceptExistingOnly(this Option<FileInfo> option)
         /// <returns>The option being extended.</returns>
         public static Option<DirectoryInfo> AcceptExistingOnly(this Option<DirectoryInfo> option)
         {
-            option.Argument.AddValidator(Validate.DirectoryExists);
+            option.Argument.Validators.Add(Validate.DirectoryExists);
             return option;
         }
 
@@ -40,7 +40,7 @@ public static Option<DirectoryInfo> AcceptExistingOnly(this Option<DirectoryInfo
         /// <returns>The option being extended.</returns>
         public static Option<FileSystemInfo> AcceptExistingOnly(this Option<FileSystemInfo> option)
         {
-            option.Argument.AddValidator(Validate.FileOrDirectoryExists);
+            option.Argument.Validators.Add(Validate.FileOrDirectoryExists);
             return option;
         }
 

src/System.CommandLine/Option{T}.cs

@@ -132,6 +132,16 @@ public Option<T> AddCompletions(Func<CompletionContext, IEnumerable<CompletionIt
             return this;
         }
 
+        /// <summary>
+        /// Adds a validator that will be called when the option is matched by the parser.
+        /// </summary>
+        /// <param name="validate">An action used to validate the <see cref="OptionResult"/> produced during parsing.</param>
+        public Option<T> AddValidator(Action<OptionResult> validate)
+        {
+            Validators.Add(validate);
+            return this;
+        }
+
         /// <summary>
         /// Configures the option to accept only values representing legal file paths.
         /// </summary>