fix #818

Author: jonsequitur

src/System.CommandLine.Tests/ValidationMessageLocalizationTests.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 using System.Collections.Generic;
+using System.CommandLine.Builder;
 using System.CommandLine.Parsing;
 using FluentAssertions;
 using System.Linq;
@@ -32,6 +33,29 @@ public void Default_validation_messages_can_be_replaced_in_order_to_add_localiza
                   .Contain("the-message");
         }
 
+        [Fact]
+        public void Default_validation_messages_can_be_replaced_using_CommandLineBuilder_in_order_to_add_localization_support()
+        {
+            var messages = new FakeValidationMessages("the-message");
+
+            var parser = new CommandLineBuilder(new Command("the-command")
+                         {
+                             new Argument
+                             {
+                                 Arity = ArgumentArity.ExactlyOne
+                             }
+                         })
+                         .UseValidationMessages(messages)
+                         .Build();
+
+            var result = parser.Parse("the-command");
+
+            result.Errors
+                  .Select(e => e.Message)
+                  .Should()
+                  .Contain("the-message");
+        }
+
         public class FakeValidationMessages : ValidationMessages
         {
             private readonly string message;

src/System.CommandLine/Builder/CommandLineBuilder.cs

@@ -29,6 +29,8 @@ public CommandLineBuilder(Command rootCommand = null)
 
         internal Option HelpOption { get; set; }
 
+        internal ValidationMessages ValidationMessages { get; set; }
+
         public Parser Build()
         {
             var rootCommand = Command;
@@ -38,7 +40,7 @@ public Parser Build()
                     new[] { rootCommand },
                     enablePosixBundling: EnablePosixBundling,
                     enableDirectives: EnableDirectives,
-                    validationMessages: ValidationMessages.Instance,
+                    validationMessages: ValidationMessages,
                     responseFileHandling: ResponseFileHandling,
                     middlewarePipeline: _middlewareList?.OrderBy(m => m.order)
                                                        .Select(m => m.middleware)

src/System.CommandLine/Builder/CommandLineBuilderExtensions.cs

@@ -412,6 +412,14 @@ public static CommandLineBuilder UseTypoCorrections(
             return builder;
         }
 
+        public static CommandLineBuilder UseValidationMessages(
+            this CommandLineBuilder builder,
+            ValidationMessages validationMessages)
+        {
+            builder.ValidationMessages = validationMessages;
+            return builder;
+        }
+
         public static CommandLineBuilder UseVersionOption(
             this CommandLineBuilder builder)
         {