Fix parent schema discriminator validation

src/Microsoft.OpenApi/Validations/Rules/OpenApiSchemaRules.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT license. 
 
-using Microsoft.OpenApi.Any;
 using Microsoft.OpenApi.Models;
 using Microsoft.OpenApi.Properties;
 using System.Collections.Generic;
@@ -11,7 +10,6 @@ namespace Microsoft.OpenApi.Validations.Rules
     /// <summary>
     /// The validation rules for <see cref="OpenApiSchema"/>.
     /// </summary>
-
     [OpenApiRule]
     public static class OpenApiSchemaRules
     {
@@ -70,15 +68,74 @@ public static class OpenApiSchemaRules
 
                     if (schema.Reference != null && schema.Discriminator != null)
                     {
-                        if (!schema.Required.Contains(schema.Discriminator?.PropertyName))
+                        var discriminatorName = schema.Discriminator?.PropertyName;
+
+                        if (!ValidateChildSchemaAgainstDiscriminator(schema, discriminatorName))
                         {
                             context.CreateError(nameof(ValidateSchemaDiscriminator),
-                                                string.Format(SRResource.Validation_SchemaRequiredFieldListMustContainThePropertySpecifiedInTheDiscriminator,
-                                                                                schema.Reference.Id, schema.Discriminator.PropertyName));
+                            string.Format(SRResource.Validation_SchemaRequiredFieldListMustContainThePropertySpecifiedInTheDiscriminator,
+                                schema.Reference.Id, discriminatorName));
                         }
                     }
 
                     context.Exit();
                 });
+
+        /// <summary>
+        /// Validates the property name in the discriminator against the ones present in the children schema
+        /// </summary>
+        /// <param name="schema">The parent schema.</param>
+        /// <param name="discriminatorName">Adds support for polymorphism. The discriminator is an object name that is used to differentiate
+        /// between other schemas which may satisfy the payload description.</param>
+        public static bool ValidateChildSchemaAgainstDiscriminator(OpenApiSchema schema, string discriminatorName)
+        {
+            if (!schema.Required?.Contains(discriminatorName) ?? false)
+            {
+                // recursively check nested schema.OneOf, schema.AnyOf or schema.AllOf and their required fields for the discriminator
+                if (schema.OneOf.Count != 0)
+                {
+                    return TraverseSchemaElements(discriminatorName, schema.OneOf);
+                }
+                if (schema.AnyOf.Count != 0)
+                {
+                    return TraverseSchemaElements(discriminatorName, schema.AnyOf);
+                }
+                if (schema.AllOf.Count != 0)
+                {
+                    return TraverseSchemaElements(discriminatorName, schema.AllOf);
+                }
+            }
+            else
+            {
+                return true;
+            }
+
+            return false;
+        }
+
+        /// <summary>
+        /// Traverses the schema elements and checks whether the schema contains the discriminator.
+        /// </summary>
+        /// <param name="discriminatorName">Adds support for polymorphism. The discriminator is an object name that is used to differentiate
+        /// between other schemas which may satisfy the payload description.</param>
+        /// <param name="childSchema">The child schema.</param>
+        /// <returns></returns>
+        public static bool TraverseSchemaElements(string discriminatorName, IList<OpenApiSchema> childSchema)
+        {
+            foreach (var childItem in childSchema)
+            {
+                if ((!childItem.Properties?.ContainsKey(discriminatorName) ?? false) &&
+                                    (!childItem.Required?.Contains(discriminatorName) ?? false))
+                {
+                    return ValidateChildSchemaAgainstDiscriminator(childItem, discriminatorName);
+                }
+                else
+                {
+                    return true;
+                }
+            }
+
+            return false;
+        }
     }
 }

test/Microsoft.OpenApi.Tests/PublicApi/PublicApi.approved.txt

@@ -1283,6 +1283,8 @@ namespace Microsoft.OpenApi.Validations.Rules
     {
         public static Microsoft.OpenApi.Validations.ValidationRule<Microsoft.OpenApi.Models.OpenApiSchema> SchemaMismatchedDataType { get; }
         public static Microsoft.OpenApi.Validations.ValidationRule<Microsoft.OpenApi.Models.OpenApiSchema> ValidateSchemaDiscriminator { get; }
+        public static bool TraverseSchemaElements(string discriminatorName, System.Collections.Generic.IList<Microsoft.OpenApi.Models.OpenApiSchema> childSchema) { }
+        public static bool ValidateChildSchemaAgainstDiscriminator(Microsoft.OpenApi.Models.OpenApiSchema schema, string discriminatorName) { }
     }
     [Microsoft.OpenApi.Validations.Rules.OpenApiRule]
     public static class OpenApiServerRules

test/Microsoft.OpenApi.Tests/Validations/OpenApiSchemaValidationTests.cs

@@ -268,5 +268,60 @@ public void ValidateSchemaRequiredFieldListMustContainThePropertySpecifiedInTheD
                                     "schema1", "property1"))
             });
         }
+
+        [Fact]
+        public void ValidateOneOfSchemaPropertyNameContainsPropertySpecifiedInTheDiscriminator()
+        {
+            // Arrange
+            var components = new OpenApiComponents
+            {
+                Schemas = 
+                {
+                    {
+                        "Person",
+                        new OpenApiSchema
+                        {
+                            Type = "array",
+                            Discriminator = new OpenApiDiscriminator
+                            {
+                                PropertyName = "type"
+                            },
+                            OneOf = new List<OpenApiSchema>
+                            {
+                                new OpenApiSchema
+                                {
+                                    Properties =
+                                    {
+                                        {
+                                            "type",
+                                            new OpenApiSchema
+                                            {
+                                                Type = "array"
+                                            }
+                                        }
+                                    },
+                                    Reference = new OpenApiReference
+                                    {
+                                        Type = ReferenceType.Schema,
+                                        Id = "Person"
+                                    }
+                                }
+                            },
+                            Reference = new OpenApiReference { Id = "Person" }
+                        }
+                    }                    
+                }
+            };
+
+            // Act
+            var validator = new OpenApiValidator(ValidationRuleSet.GetDefaultRuleSet());
+            var walker = new OpenApiWalker(validator);
+            walker.Walk(components);
+
+            var errors = validator.Errors;
+
+            //Assert
+            errors.Should().BeEmpty();
+        }
     }
 }