Apply only a SchemaFilter to create the Description on the SwaggerUi

src/Swashbuckle.AspNetCore.SwaggerGen/SwaggerGenerator/SwaggerGenerator.cs

@@ -375,12 +375,21 @@ private OpenApiParameter GenerateParameter(
                     apiParameter.RouteInfo)
                 : new OpenApiSchema { Type = "string" };
 
+            var description = schema.Description;
+            if (string.IsNullOrEmpty(description)
+                && !string.IsNullOrEmpty(schema?.Reference?.Id)
+                && schemaRepository.Schemas.TryGetValue(schema.Reference.Id, out var openApiSchema))
+            {
+                description = openApiSchema.Description;
+            }
+
             var parameter = new OpenApiParameter
             {
                 Name = name,
                 In = location,
                 Required = isRequired,
-                Schema = schema
+                Schema = schema,
+                Description = description
             };
 
             var filterContext = new ParameterFilterContext(

test/Swashbuckle.AspNetCore.SwaggerGen.Test/Fixtures/FakeICompositeMetadataDetailsProvider.cs

@@ -7,7 +7,7 @@ internal class FakeICompositeMetadataDetailsProvider : ICompositeMetadataDetails
     {
         public void CreateBindingMetadata(BindingMetadataProviderContext context)
         {
-            throw new NotImplementedException();
+            context.BindingMetadata.IsBindingAllowed = true;
         }
 
         public void CreateDisplayMetadata(DisplayMetadataProviderContext context)

test/Swashbuckle.AspNetCore.SwaggerGen.Test/Fixtures/TestEnumSchemaFilter.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Linq;
+using System.Text;
+using Microsoft.OpenApi.Any;
+using Microsoft.OpenApi.Models;
+
+namespace Swashbuckle.AspNetCore.SwaggerGen.Test.Fixtures
+{
+    internal class TestEnumSchemaFilter : ISchemaFilter
+    {
+        public void Apply(OpenApiSchema schema, SchemaFilterContext context)
+        {
+            bool isEnumArgument = (context.Type?.GenericTypeArguments?.Length ?? 0) == 1 && context.Type.GenericTypeArguments.All(b => b.IsEnum);
+            var isEnumArray = context.Type.IsArray && context.Type.GetElementType().IsEnum;
+            if (context.Type.IsEnum || isEnumArgument || isEnumArray)
+            {
+                var enumType = (context.Type.IsEnum, isEnumArgument, isEnumArray) switch
+                {
+                    (true, _, _) => context.Type,
+                    (_, true, _) => context.Type.GenericTypeArguments.First(),
+                    _ => context.Type.GetElementType()
+                };
+                StringBuilder stringBuilder = new("<p>Members:</p><ul>");
+                OpenApiArray names = [];
+                foreach (var enumValue in Enum.GetValues(enumType))
+                {
+                    if (enumValue is Enum value)
+                    {
+                        names.Add(new OpenApiString(value.ToString()));
+                        stringBuilder.Append($"<li>{value} - {value:d}</li>");
+                    }
+                }
+                schema.Extensions.Add("x-enum-varnames", names);
+                schema.Description = stringBuilder.Append("</ul>").ToString();
+            }
+        }
+    }
+}

test/Swashbuckle.AspNetCore.SwaggerGen.Test/SwaggerGenerator/SwaggerGeneratorTests.cs

@@ -1723,15 +1723,69 @@ public void GetSwagger_Works_As_Expected_When_FromForm_Attribute_With_SwaggerIgn
             Assert.Equal(new[] { nameof(SwaggerIngoreAnnotatedType.NotIgnoredString) }, mediaType.Encoding.Keys);
         }
 
+        [Fact]
+        public void GetSwagger_Copies_Description_From_GeneratedSchema()
+        {
+            var propertyEnum = typeof(TypeWithDefaultAttributeOnEnum).GetProperty(nameof(TypeWithDefaultAttributeOnEnum.EnumWithDefault));
+            var modelMetadataForEnum = new DefaultModelMetadata(
+                                    new DefaultModelMetadataProvider(new FakeICompositeMetadataDetailsProvider()),
+                                    new FakeICompositeMetadataDetailsProvider(),
+                                    new DefaultMetadataDetails(ModelMetadataIdentity.ForProperty(propertyEnum, typeof(IntEnum), typeof(TypeWithDefaultAttributeOnEnum)), ModelAttributes.GetAttributesForProperty(typeof(TypeWithDefaultAttributeOnEnum), propertyEnum)));
+
+            var propertyEnumArray = typeof(TypeWithDefaultAttributeOnEnum).GetProperty(nameof(TypeWithDefaultAttributeOnEnum.EnumArrayWithDefault));
+            var modelMetadataForEnumArray = new DefaultModelMetadata(
+                                    new DefaultModelMetadataProvider(new FakeICompositeMetadataDetailsProvider()),
+                                    new FakeICompositeMetadataDetailsProvider(),
+                                    new DefaultMetadataDetails(ModelMetadataIdentity.ForProperty(propertyEnumArray, typeof(IntEnum[]), typeof(TypeWithDefaultAttributeOnEnum)), ModelAttributes.GetAttributesForProperty(typeof(TypeWithDefaultAttributeOnEnum), propertyEnumArray)));
+            var subject = Subject(
+               apiDescriptions:
+               [
+                   ApiDescriptionFactory.Create<FakeController>(
+                        c => nameof(c.ActionHavingFromFormAttributeWithSwaggerIgnore),
+                        groupName: "v1",
+                        httpMethod: "POST",
+                        relativePath: "resource",
+                        parameterDescriptions: new[]
+                        {
+                            new ApiParameterDescription
+                            {
+                                Name = nameof(TypeWithDefaultAttributeOnEnum.EnumWithDefault),
+                                Source = BindingSource.Query,
+                                Type = typeof(IntEnum),
+                                ModelMetadata = modelMetadataForEnum
+                            },
+                            new ApiParameterDescription
+                            {
+                                Name = nameof(TypeWithDefaultAttributeOnEnum.EnumArrayWithDefault),
+                                Source = BindingSource.Query,
+                                Type = typeof(IntEnum[]),
+                                ModelMetadata = modelMetadataForEnumArray
+                            }
+                        })
+               ],
+               schemaFilters: [new TestEnumSchemaFilter()]
+           );
+            var document = subject.GetSwagger("v1");
+
+            var operation = document.Paths["/resource"].Operations[OperationType.Post];
+            Assert.NotEmpty(operation.Parameters);
+            Assert.Equal(nameof(TypeWithDefaultAttributeOnEnum.EnumWithDefault), operation.Parameters[0].Name);
+            Assert.NotEmpty(operation.Parameters[0].Description);
+            Assert.Equal(nameof(TypeWithDefaultAttributeOnEnum.EnumArrayWithDefault), operation.Parameters[1].Name);
+            Assert.NotEmpty(operation.Parameters[1].Description);
+
+        }
+
         private static SwaggerGenerator Subject(
             IEnumerable<ApiDescription> apiDescriptions,
             SwaggerGeneratorOptions options = null,
-            IEnumerable<AuthenticationScheme> authenticationSchemes = null)
+            IEnumerable<AuthenticationScheme> authenticationSchemes = null,
+            List<ISchemaFilter> schemaFilters = null)
         {
             return new SwaggerGenerator(
                 options ?? DefaultOptions,
                 new FakeApiDescriptionGroupCollectionProvider(apiDescriptions),
-                new SchemaGenerator(new SchemaGeneratorOptions(), new JsonSerializerDataContractResolver(new JsonSerializerOptions())),
+                new SchemaGenerator(new SchemaGeneratorOptions() { SchemaFilters = schemaFilters ?? [] }, new JsonSerializerDataContractResolver(new JsonSerializerOptions())),
                 new FakeAuthenticationSchemeProvider(authenticationSchemes ?? Enumerable.Empty<AuthenticationScheme>())
             );
         }

test/Swashbuckle.AspNetCore.TestSupport/Fixtures/TypeWithDefaultAttributeOnEnum.cs

@@ -6,5 +6,7 @@ public class TypeWithDefaultAttributeOnEnum
     {
         [DefaultValue(IntEnum.Value4)]
         public IntEnum EnumWithDefault { get; set; }
+        [DefaultValue(new IntEnum[] { IntEnum.Value4 })]
+        public IntEnum[] EnumArrayWithDefault { get; set; }
     }
 }