Updated walkers and added validate method

Author: darrelmiller

src/Microsoft.OpenApi/Extensions/OpenApiElementExtensions.cs

@@ -0,0 +1,31 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT license. 
+
+using System;
+using System.Collections.Generic;
+using Microsoft.OpenApi.Interfaces;
+using Microsoft.OpenApi.Models;
+using Microsoft.OpenApi.Services;
+using Microsoft.OpenApi.Validations;
+
+namespace Microsoft.OpenApi.Extensions
+{
+    /// <summary>
+    /// Extension methods that apply across all OpenAPIElements
+    /// </summary>
+    public static class OpenApiElementExtensions
+    {
+        /// <summary>
+        /// Validate element and all child elements
+        /// </summary>
+        /// <typeparam name="T"></typeparam>
+        /// <param name="element"></param>
+        /// <returns></returns>
+        public static IEnumerable<ValidationError> Validate(this IOpenApiElement element)         {
+            var validator = new OpenApiValidator();
+            var walker = new OpenApiWalker(validator);
+            walker.Walk(element);
+            return validator.Errors;
+        }
+    }
+}

src/Microsoft.OpenApi/Services/OpenApiVisitorBase.cs

@@ -196,12 +196,27 @@ public virtual void Visit(OpenApiLink link)
         {
         }
 
+        /// <summary>
+        /// Visits <see cref="OpenApiCallback"/>
+        /// </summary>
+        public virtual void Visit(OpenApiCallback callback)
+        {
+        }
+
         /// <summary>
         /// Visits <see cref="OpenApiTag"/>
         /// </summary>
         public virtual void Visit(OpenApiTag tag)
         {
         }
+
+        /// <summary>
+        /// Visits <see cref="OpenApiHeader"/>
+        /// </summary>
+        public virtual void Visit(OpenApiHeader tag)
+        {
+        }
+
         /// <summary>
         /// Visits <see cref="OpenApiOAuthFlow"/>
         /// </summary>
@@ -210,7 +225,14 @@ public virtual void Visit(OpenApiOAuthFlow openApiOAuthFlow)
         }
 
         /// <summary>
-        /// Visits <see cref="OpenApiOAuthFlow"/>
+        /// Visits <see cref="OpenApiSecurityRequirement"/>
+        /// </summary>
+        public virtual void Visit(OpenApiSecurityRequirement securityRequirement)
+        {
+        }
+
+        /// <summary>
+        /// Visits list of <see cref="OpenApiTag"/>
         /// </summary>
         public virtual void Visit(IList<OpenApiTag> openApiTags)
         {