Fix #1597 child rules not working as expeted with rulesets.

Changelog.txt

@@ -1,3 +1,6 @@
+9.4.0 - 14 January 2021
+ChildRules now work as expected when inside a ruleset (#1597)
+
 9.3.0 - 10 November 2020
 Support for .NET 5
 Improvements to LanguageManager's lazy loading of resources.

src/FluentValidation.Tests/ChildRulesTests.cs

@@ -43,5 +43,43 @@ public class ChildRulesTests {
 			result.Errors[0].PropertyName.ShouldEqual("Orders[0].ProductName");
 			result.Errors[1].PropertyName.ShouldEqual("Orders[1].Amount");
 		}
+
+		[Fact]
+		public void ChildRules_works_with_RuleSet() {
+			var validator = new RulesetChildRulesValidator();
+
+			// As Child Rules are implemented as a child validator, the child rules are technically
+			// not inside the "testing" ruleset (going by the usual way rulesets cascade).
+			// However, child rules should still be executed.
+			var result = validator.Validate(new Person {
+				Orders = new List<Order> {
+					new Order()
+				}
+			}, options => options.IncludeRuleSets("testing"));
+
+			result.Errors.Count.ShouldEqual(2);
+			result.Errors[0].PropertyName.ShouldEqual("Surname");
+			result.Errors[1].PropertyName.ShouldEqual("Orders[0].ProductName");
+
+			// They shouldn't be executed if a different ruleset is chosen.
+			result = validator.Validate(new Person {
+				Orders = new List<Order> {
+					new Order()
+				}
+			}, options => options.IncludeRuleSets("other"));
+
+			result.Errors.Count.ShouldEqual(0);
+		}
+
+		private class RulesetChildRulesValidator : AbstractValidator<Person>  {
+			public RulesetChildRulesValidator() {
+				RuleSet("testing", () => {
+					RuleFor(a => a.Surname).NotEmpty();
+					RuleForEach(a => a.Orders).ChildRules(child => {
+						child.RuleFor(o => o.ProductName).NotEmpty();
+					});
+				});
+			}
+		}
 	}
 }

src/FluentValidation/DefaultValidatorExtensions.cs

@@ -1024,7 +1024,7 @@ public static partial class DefaultValidatorExtensions {
 			if (action == null) throw new ArgumentNullException(nameof(action));
 			var validator = new InlineValidator<TProperty>();
 			action(validator);
-			return ruleBuilder.SetValidator(validator);
+			return ruleBuilder.SetValidator(validator, "*");
 		}
 
 		/// <summary>

src/FluentValidation/FluentValidation.csproj

@@ -5,6 +5,9 @@
     <PackageReleaseNotes>
 FluentValidation 9 is a major release. Please read the upgrade notes at https://docs.fluentvalidation.net/en/latest/upgrading-to-9.html
 
+Changes in 9.4.0:
+* ChildRules now work as expected when inside a ruleset
+
 Changes in 9.3.0:
 * Improvements to LanguageManager's lazy loading of resources.
 * Deprecate IStringSource and its implementors. Use delegates instead.