Use ParameterInfo for getting metadata of a parameter to show the correct information in ApiExplorer

[Fixes #7435] 2.1-Preview 1: IsBindingRequired and IsRequired still false with RequiredAttribute on controller parameter.

src/Microsoft.AspNetCore.Mvc.ApiExplorer/DefaultApiDescriptionProvider.cs

@@ -162,7 +162,23 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
                 foreach (var actionParameter in context.ActionDescriptor.Parameters)
                 {
                     var visitor = new PseudoModelBindingVisitor(context, actionParameter);
-                    var metadata = _modelMetadataProvider.GetMetadataForType(actionParameter.ParameterType);
+
+                    ModelMetadata metadata = null;
+                    if (actionParameter is ControllerParameterDescriptor controllerParameterDescriptor &&
+                        _modelMetadataProvider is ModelMetadataProvider provider)
+                    {
+                        // The default model metadata provider derives from ModelMetadataProvider
+                        // and can therefore supply information about attributes applied to parameters.
+                        metadata = provider.GetMetadataForParameter(controllerParameterDescriptor.ParameterInfo);
+                    }
+                    else
+                    {
+                        // For backward compatibility, if there's a custom model metadata provider that
+                        // only implements the older IModelMetadataProvider interface, access the more
+                        // limited metadata information it supplies. In this scenario, validation attributes
+                        // are not supported on parameters.
+                        metadata = _modelMetadataProvider.GetMetadataForType(actionParameter.ParameterType);
+                    }
 
                     var bindingContext = ApiParameterDescriptionContext.GetContext(
                         metadata,

test/Microsoft.AspNetCore.Mvc.ApiExplorer.Test/DefaultApiDescriptionProviderTest.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
+using System.ComponentModel.DataAnnotations;
 using System.Linq;
 using System.Reflection;
 using System.Text;
@@ -912,6 +913,25 @@ namespace Microsoft.AspNetCore.Mvc.Description
             Assert.Equal(typeof(string), parameter.Type);
         }
 
+        [Fact]
+        public void GetApiDescription_ParameterDescription_IsRequired()
+        {
+            // Arrange
+            var action = CreateActionDescriptor(nameof(RequiredParameter));
+
+            // Act
+            var descriptions = GetApiDescriptions(action);
+
+            // Assert
+            var description = Assert.Single(descriptions);
+            var parameter = Assert.Single(description.ParameterDescriptions);
+            Assert.Equal("name", parameter.Name);
+            Assert.Same(BindingSource.ModelBinding, parameter.Source);
+            Assert.Equal(typeof(string), parameter.Type);
+            Assert.True(parameter.ModelMetadata.IsRequired);
+            Assert.True(parameter.ModelMetadata.IsBindingRequired);
+        }
+
         [Fact]
         public void GetApiDescription_ParameterDescription_SourceFromRouteData()
         {
@@ -1472,11 +1492,12 @@ namespace Microsoft.AspNetCore.Mvc.Description
             action.Parameters = new List<ParameterDescriptor>();
             foreach (var parameter in action.MethodInfo.GetParameters())
             {
-                action.Parameters.Add(new ParameterDescriptor()
+                action.Parameters.Add(new ControllerParameterDescriptor()
                 {
                     Name = parameter.Name,
                     ParameterType = parameter.ParameterType,
-                    BindingInfo = BindingInfo.GetBindingInfo(parameter.GetCustomAttributes().OfType<object>())
+                    BindingInfo = BindingInfo.GetBindingInfo(parameter.GetCustomAttributes().OfType<object>()),
+                    ParameterInfo = parameter
                 });
             }
 
@@ -1552,6 +1573,10 @@ namespace Microsoft.AspNetCore.Mvc.Description
         {
         }
 
+        private void RequiredParameter([BindRequired, Required] string name)
+        {
+        }
+
         private void AcceptsProduct_Body([FromBody] Product product)
         {
         }