Adding support for custom ValidationResult (derived class) in CustomValidationAttribute

Commit migrated from dotnet/corefx@27af01c

Author: Liero

src/libraries/System.ComponentModel.Annotations/src/System/ComponentModel/DataAnnotations/CustomValidationAttribute.cs

@@ -242,8 +242,8 @@ private string ValidateMethodParameter()
                 return SR.Format(SR.CustomValidationAttribute_Method_Not_Found, Method, ValidatorType.Name);
             }
 
-            // Method must return a ValidationResult
-            if (methodInfo.ReturnType != typeof(ValidationResult))
+            // Method must return a ValidationResult or derived class
+             if (!typeof(ValidationResult).IsAssignableFrom(methodInfo.ReturnType))
             {
                 return SR.Format(SR.CustomValidationAttribute_Method_Must_Return_ValidationResult, Method, ValidatorType.Name);
             }

src/libraries/System.ComponentModel.Annotations/tests/System/ComponentModel/DataAnnotations/CustomValidationAttributeTests.cs

@@ -63,6 +63,7 @@ protected override IEnumerable<TestCase> InvalidValues()
 
         [Theory]
         [InlineData(typeof(CustomValidator), "SomeMethod")]
+        [InlineData(typeof(CustomValidator), nameof(CustomValidator.ValidationMethodDerivedReturnTypeReturnsSomeError))]
         [InlineData(null, null)]
         [InlineData(typeof(string), "")]
         [InlineData(typeof(int), " \t\r\n")]
@@ -178,6 +179,14 @@ public static void Validate_MethodThrowsCustomException_IsNotCaught()
             AssertExtensions.Throws<ArgumentException>(null, () => attribute.Validate(new IConvertibleImplementor(), s_testValidationContext));
         }
 
+        [Fact]
+        public static void GetValidationResult_MethodReturnDerivedValidationResult_ReturnsExpected()
+        {
+            CustomValidationAttribute attribute = GetAttribute(nameof(CustomValidator.ValidationMethodDerivedReturnTypeReturnsSomeError));
+            ValidationResult validationResult = attribute.GetValidationResult(new object(), s_testValidationContext);
+            Assert.Equal(DerivedValidationResult.SomeError, validationResult);
+        }
+
         internal class NonPublicCustomValidator
         {
             public static ValidationResult ValidationMethodOneArg(object o) => ValidationResult.Success;
@@ -210,6 +219,9 @@ public static ValidationResult ValidationMethodThreeArgs(object o, ValidationCon
                 return ValidationResult.Success;
             }
 
+            public static DerivedValidationResult ValidationMethodDerivedReturnTypeReturnsSomeError(object o) =>
+                DerivedValidationResult.SomeError;
+
             public static ValidationResult CorrectValidationMethodOneArg(object o)
             {
                 if (o is string) { return ValidationResult.Success; }
@@ -272,5 +284,17 @@ public struct TestStruct
         }
 
         public struct GenericStruct<T> { }
+
+        public class DerivedValidationResult : ValidationResult
+        {
+            public DerivedValidationResult(string errorMessage): base(errorMessage)
+            {
+            }
+
+            public static readonly DerivedValidationResult SomeError =
+                new DerivedValidationResult("Some Error") { AdditionalData = "Additional Data" }; 
+
+            public string AdditionalData { get; set; }
+        }
     }
 }