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 +1,34 @@
+using System;
+using System.Linq;
+using System.Text;
+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>");
+                foreach (var enumValue in Enum.GetValues(enumType))
+                {
+                    if (enumValue is Enum value)
+                    {
+                        stringBuilder.Append($"<li>{value} - {value:d}</li>");
+                    }
+                }
+                schema.Description = stringBuilder.Append("</ul>").ToString();
+            }
+        }
+    }
+}

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

@@ -1723,15 +1723,68 @@ 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.Equal(document.Components.Schemas[nameof(IntEnum)].Description, operation.Parameters[0].Description);
+            Assert.Equal(nameof(TypeWithDefaultAttributeOnEnum.EnumArrayWithDefault), operation.Parameters[1].Name);
+            Assert.Equal(document.Components.Schemas[nameof(IntEnum)].Description, 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.SwaggerGen.Test/SwaggerGeneratorVerifyTests/SwaggerGeneratorVerifyTests.GetSwagger_Copies_Description_From_GeneratedSchema.verified.txt

@@ -0,0 +1,130 @@
+{
+  Info: {
+    Title: Test API,
+    Version: V1
+  },
+  Paths: {
+    /resource: {
+      Operations: {
+        Post: {
+          Tags: [
+            {
+              Name: Fake,
+              UnresolvedReference: false
+            }
+          ],
+          Parameters: [
+            {
+              UnresolvedReference: false,
+              Name: EnumWithDefault,
+              In: Query,
+              Description: <p>Members:</p><ul><li>Value2 - 2</li><li>Value4 - 4</li><li>Value8 - 8</li></ul>,
+              Required: false,
+              Deprecated: false,
+              AllowEmptyValue: false,
+              Style: Form,
+              Explode: true,
+              AllowReserved: false,
+              Schema: {
+                ReadOnly: false,
+                WriteOnly: false,
+                AdditionalPropertiesAllowed: true,
+                Nullable: false,
+                Deprecated: false,
+                UnresolvedReference: false,
+                Reference: {
+                  IsFragrament: false,
+                  Type: Schema,
+                  Id: IntEnum,
+                  IsExternal: false,
+                  IsLocal: true,
+                  ReferenceV3: #/components/schemas/IntEnum,
+                  ReferenceV2: #/definitions/IntEnum
+                }
+              }
+            },
+            {
+              UnresolvedReference: false,
+              Name: EnumArrayWithDefault,
+              In: Query,
+              Description: <p>Members:</p><ul><li>Value2 - 2</li><li>Value4 - 4</li><li>Value8 - 8</li></ul>,
+              Required: false,
+              Deprecated: false,
+              AllowEmptyValue: false,
+              Style: Form,
+              Explode: true,
+              AllowReserved: false,
+              Schema: {
+                Type: array,
+                Description: <p>Members:</p><ul><li>Value2 - 2</li><li>Value4 - 4</li><li>Value8 - 8</li></ul>,
+                Default: [
+                  {
+                    Value: 4
+                  }
+                ],
+                ReadOnly: false,
+                WriteOnly: false,
+                Items: {
+                  ReadOnly: false,
+                  WriteOnly: false,
+                  AdditionalPropertiesAllowed: true,
+                  Nullable: false,
+                  Deprecated: false,
+                  UnresolvedReference: false,
+                  Reference: {
+                    IsFragrament: false,
+                    Type: Schema,
+                    Id: IntEnum,
+                    IsExternal: false,
+                    IsLocal: true,
+                    ReferenceV3: #/components/schemas/IntEnum,
+                    ReferenceV2: #/definitions/IntEnum
+                  }
+                },
+                AdditionalPropertiesAllowed: true,
+                Nullable: false,
+                Deprecated: false,
+                UnresolvedReference: false
+              }
+            }
+          ],
+          Responses: {
+            200: {
+              Description: OK,
+              UnresolvedReference: false
+            }
+          },
+          Deprecated: false
+        }
+      },
+      UnresolvedReference: false
+    }
+  },
+  Components: {
+    Schemas: {
+      IntEnum: {
+        Type: integer,
+        Format: int32,
+        Description: <p>Members:</p><ul><li>Value2 - 2</li><li>Value4 - 4</li><li>Value8 - 8</li></ul>,
+        ReadOnly: false,
+        WriteOnly: false,
+        AdditionalPropertiesAllowed: true,
+        Enum: [
+          {
+            Value: 2
+          },
+          {
+            Value: 4
+          },
+          {
+            Value: 8
+          }
+        ],
+        Nullable: false,
+        Deprecated: false,
+        UnresolvedReference: false
+      }
+    }
+  },
+  HashCode: 29A4A89ADE3B75E921A9EF9CE77F3E1517293B167A0B1513F55C57F3E84194193E8B24F875170DE0524C73CF5AB9DDCDF6556F1BDC2E6EA1F8171340F4C0F0B1
+}

test/Swashbuckle.AspNetCore.SwaggerGen.Test/SwaggerGeneratorVerifyTests/SwaggerGeneratorVerifyTests.cs

@@ -1102,15 +1102,63 @@ public Task ActionHavingFromFormAttributeWithSwaggerIgnore()
         return Verifier.Verify(document);
     }
 
+    [Fact]
+    public Task 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");
+
+        return Verifier.Verify(document);
+    }
+
     private static SwaggerGenerator Subject(
-        IEnumerable<ApiDescription> apiDescriptions,
-        SwaggerGeneratorOptions options = null,
-        IEnumerable<AuthenticationScheme> authenticationSchemes = null)
+            IEnumerable<ApiDescription> apiDescriptions,
+            SwaggerGeneratorOptions options = 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; }
     }
 }