Expose ParameterInfo for Minimal Actions API Explorer (#36439) (#36547)

* Expose ParameterInfo for Minimal Actions API Explorer

Populate the ParameterDescriptor for Minimal Actions parameters with
a type that implements IParameterInfoParameterDescriptor so that any
custom attributes on the parameter can be inspected.
Relates to #36438.

* Remove file-scoped namespace

Addresses review feedback.

Co-authored-by: Martin Costello <martin@martincostello.com>

src/Mvc/Mvc.ApiExplorer/src/EndpointMetadataApiDescriptionProvider.cs

 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System;
 using System.Linq;
 using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Security.Claims;
-using System.Threading;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Http.Metadata;
 using Microsoft.AspNetCore.Mvc.Abstractions;
@@ -162,6 +160,7 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
             var nullabilityContext = new NullabilityInfoContext();
             var nullability = nullabilityContext.Create(parameter);
             var isOptional = parameter.HasDefaultValue || nullability.ReadState != NullabilityState.NotNull || allowEmpty;
+            var parameterDescriptor = CreateParameterDescriptor(parameter);
 
             return new ApiParameterDescription
             {
@@ -170,10 +169,19 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
                 Source = source,
                 DefaultValue = parameter.DefaultValue,
                 Type = parameter.ParameterType,
-                IsRequired = !isOptional
+                IsRequired = !isOptional,
+                ParameterDescriptor = parameterDescriptor
             };
         }
 
+        private static ParameterDescriptor CreateParameterDescriptor(ParameterInfo parameter)
+            => new EndpointParameterDescriptor
+            {
+                Name = parameter.Name ?? string.Empty,
+                ParameterInfo = parameter,
+                ParameterType = parameter.ParameterType,
+            };
+
         // TODO: Share more of this logic with RequestDelegateFactory.CreateArgument(...) using RequestDelegateFactoryUtilities
         // which is shared source.
         private (BindingSource, string, bool) GetBindingSourceAndName(ParameterInfo parameter, RoutePattern pattern)

src/Mvc/Mvc.ApiExplorer/src/EndpointParameterDescriptor.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Reflection;
+using Microsoft.AspNetCore.Mvc.Abstractions;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
+
+namespace Microsoft.AspNetCore.Mvc.ApiExplorer
+{
+    internal sealed class EndpointParameterDescriptor : ParameterDescriptor, IParameterInfoParameterDescriptor
+    {
+        public ParameterInfo ParameterInfo { get; set; } = default!;
+    }
+}

src/Mvc/Mvc.ApiExplorer/test/EndpointMetadataApiDescriptionProviderTest.cs

@@ -4,6 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.ComponentModel;
 using System.Reflection;
 using System.Security.Claims;
 using System.Threading;
@@ -11,6 +12,7 @@ using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc.Abstractions;
+using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.ModelBinding;
 using Microsoft.AspNetCore.Routing;
 using Microsoft.AspNetCore.Routing.Patterns;
@@ -268,6 +270,20 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
             AssertPathParameter(GetApiDescription(([FromRoute] int foo) => { }));
         }
 
+        [Fact]
+        public void AddsFromRouteParameterAsPathWithCustomType()
+        {
+            static void AssertPathParameter(ApiDescription apiDescription)
+            {
+                var param = Assert.Single(apiDescription.ParameterDescriptions);
+                Assert.Equal(typeof(TryParseStringRecord), param.Type);
+                Assert.Equal(typeof(TryParseStringRecord), param.ModelMetadata.ModelType);
+                Assert.Equal(BindingSource.Path, param.Source);
+            }
+
+            AssertPathParameter(GetApiDescription((TryParseStringRecord foo) => { }, "/{foo}"));
+        }
+
         [Fact]
         public void AddsFromQueryParameterAsQuery()
         {
@@ -410,6 +426,32 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
             Assert.True(barParam.IsRequired);
         }
 
+        [Fact]
+        public void TestParameterAttributesCanBeInspected()
+        {
+            var apiDescription = GetApiDescription(([Description("The name.")] string name) => { });
+            Assert.Equal(1, apiDescription.ParameterDescriptions.Count);
+
+            var nameParam = apiDescription.ParameterDescriptions[0];
+            Assert.Equal(typeof(string), nameParam.Type);
+            Assert.Equal(typeof(string), nameParam.ModelMetadata.ModelType);
+            Assert.Equal(BindingSource.Query, nameParam.Source);
+            Assert.False(nameParam.IsRequired);
+
+            Assert.NotNull(nameParam.ParameterDescriptor);
+            Assert.Equal("name", nameParam.ParameterDescriptor.Name);
+            Assert.Equal(typeof(string), nameParam.ParameterDescriptor.ParameterType);
+
+            var descriptor = Assert.IsAssignableFrom<IParameterInfoParameterDescriptor>(nameParam.ParameterDescriptor);
+
+            Assert.NotNull(descriptor.ParameterInfo);
+
+            var description = Assert.Single(descriptor.ParameterInfo.GetCustomAttributes<DescriptionAttribute>());
+
+            Assert.NotNull(description);
+            Assert.Equal("The name.", description.Description);
+        }
+
         [Fact]
         public void RespectsProducesProblemExtensionMethod()
         {