Support [JsonPolymorphic] and [JsonDerivedType] (#3170)

* Support of JsonPolymorphicAttribute
Fix integration Basic and NSwagClientExample tests to have different outputs for .net6

* Apply suggestions from code review

Co-authored-by: Martin Costello <[email protected]>

* add `Produces` to NSwagClientExmaple to strip unnecessary fields
fix `SwaggerEndpoint_ReturnsValidSwaggerJson_DotNet6` test - it wasn't using parameters

* Add README from https://github.com/domaindrivendev/Swashbuckle.AspNetCore/pull/2671/files#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5

* Apply suggestions from code review

---------

Co-authored-by: martincostello <[email protected]>
Co-authored-by: schnerring <[email protected]>

Author: 3 people

README.md

@@ -1166,7 +1166,8 @@ services.AddSwaggerGen(c =>
 });
 ```
 
-_NOTE: If you're using the [Swashbuckle Annotations library](#swashbuckleaspnetcoreannotations), it contains a custom selector that's based on the presence of `SwaggerSubType` attributes on base class definitions. This way, you can use simple attributes to explicitly list the inheritance and/or polymorphism relationships you want to expose. To enable this behavior, check out the [Annotations docs](#list-known-subtypes-for-inheritance-and-polymorphism)._
+> [!NOTE]
+> If you're using the [Swashbuckle Annotations library](#swashbuckleaspnetcoreannotations), it contains a custom selector that's based on the presence of `[JsonDerivedType]` (or `[SwaggerSubType]` for .NET 6 or earlier) attributes on base class definitions. This way, you can use simple attributes to explicitly list the inheritance and/or polymorphism relationships you want to expose. To enable this behavior, check out the [Annotations docs](#list-known-subtypes-for-inheritance-and-polymorphism).
 
 #### Describing Discriminators ####
 
@@ -1232,7 +1233,8 @@ services.AddSwaggerGen(c =>
 });
 ```
 
-_NOTE: If you're using the [Swashbuckle Annotations library](#swashbuckleaspnetcoreannotations), it contains custom selector functions that are based on the presence of `SwaggerDiscriminator` and `SwaggerSubType` attributes on base class definitions. This way, you can use simple attributes to explicitly provide discriminator metadata. To enable this behavior, check out the [Annotations docs](#enrich-polymorphic-base-classes-with-discriminator-metadata)._
+> [!NOTE]
+> If you're using the [Swashbuckle Annotations library](#swashbuckleaspnetcoreannotations), it contains custom selector functions that are based on the presence of `[JsonPolymorphic]` (or `[SwaggerDiscriminator]` for .NET 6 or earlier) and `[JsonDerivedType]` (or `[SwaggerSubType]` for .NET 6 or earlier) attributes on base class definitions. This way, you can use simple attributes to explicitly provide discriminator metadata. To enable this behavior, check out the [Annotations docs](#enrich-polymorphic-base-classes-with-discriminator-metadata).
 
 ## Swashbuckle.AspNetCore.SwaggerUI ##
 
@@ -1540,6 +1542,15 @@ services.AddSwaggerGen(c =>
 });
 
 // Shape.cs
+
+// .NET 7 or later
+[JsonDerivedType(typeof(Rectangle))]
+[JsonDerivedType(typeof(Circle))]
+public abstract class Shape
+{
+}
+
+// .NET 6 or earlier
 [SwaggerSubType(typeof(Rectangle))]
 [SwaggerSubType(typeof(Circle))]
 public abstract class Shape
@@ -1549,7 +1560,7 @@ public abstract class Shape
 
 ### Enrich Polymorphic Base Classes with Discriminator Metadata ###
 
-If you're using annotations to _explicitly_ indicate the "known" subtypes for a polymorphic base type, you can combine the `SwaggerDiscriminatorAttribute` with the `SwaggerSubTypeAttribute` to provide additional metadata about the "discriminator" property, which will then be incorporated into the generated schema definition:
+If you're using annotations to _explicitly_ indicate the "known" subtypes for a polymorphic base type, you can combine the `JsonPolymorphicAttribute` with the `JsonDerivedTypeAttribute` to provide additional metadata about the "discriminator" property, which will then be incorporated into the generated schema definition:
 
 
 ```csharp
@@ -1560,12 +1571,32 @@ services.AddSwaggerGen(c =>
 });
 
 // Shape.cs
+
+// .NET 7 or later
+[JsonPolymorphic(TypeDiscriminatorPropertyName = "shapeType")]
+[JsonDerivedType(typeof(Rectangle), "rectangle")]
+[JsonDerivedType(typeof(Circle), "circle")]
+public abstract class Shape
+{
+    // Avoid using a JsonPolymorphicAttribute.TypeDiscriminatorPropertyName
+    // that conflicts with a property in your type hierarchy.
+    // Related issue: https://github.com/dotnet/runtime/issues/72170
+}
+
+// .NET 6 or earlier
 [SwaggerDiscriminator("shapeType")]
 [SwaggerSubType(typeof(Rectangle), DiscriminatorValue = "rectangle")]
 [SwaggerSubType(typeof(Circle), DiscriminatorValue = "circle")]
 public abstract class Shape
 {
-    public ShapeType { get; set; }
+    public ShapeType ShapeType { get; set; }
+}
+
+[JsonConverter(typeof(JsonStringEnumConverter))]
+public enum ShapeType
+{
+    Circle,
+    Rectangle
 }
 ```
 

src/Swashbuckle.AspNetCore.Annotations/AnnotationsSwaggerGenOptionsExtensions.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Text.Json.Serialization;
 using Swashbuckle.AspNetCore.SwaggerGen;
 using Swashbuckle.AspNetCore.Annotations;
 
@@ -75,6 +76,17 @@ private static IEnumerable<Type> AnnotationsSubTypesSelector(Type type)
                 return obsoleteAttribute.SubTypes;
             }
 
+#if NET7_0_OR_GREATER
+            var jsonDerivedTypeAttributes = type.GetCustomAttributes(false)
+                .OfType<JsonDerivedTypeAttribute>()
+                .ToList();
+
+            if (jsonDerivedTypeAttributes.Count > 0)
+            {
+                return jsonDerivedTypeAttributes.Select(attr => attr.DerivedType);
+            }
+#endif
+
             return Enumerable.Empty<Type>();
         }
 
@@ -100,6 +112,17 @@ private static string AnnotationsDiscriminatorNameSelector(Type baseType)
                 return obsoleteAttribute.Discriminator;
             }
 
+#if NET7_0_OR_GREATER
+            var jsonPolymorphicAttributes = baseType.GetCustomAttributes(false)
+                .OfType<JsonPolymorphicAttribute>()
+                .FirstOrDefault();
+
+            if (jsonPolymorphicAttributes != null)
+            {
+                return jsonPolymorphicAttributes.TypeDiscriminatorPropertyName;
+            }
+#endif
+
             return null;
         }
 
@@ -117,6 +140,17 @@ private static string AnnotationsDiscriminatorValueSelector(Type subType)
                     return subTypeAttribute.DiscriminatorValue;
                 }
 
+#if NET7_0_OR_GREATER
+                var jsonDerivedTypeAttributes = baseType.GetCustomAttributes(false)
+                    .OfType<JsonDerivedTypeAttribute>()
+                    .FirstOrDefault(attr => attr.DerivedType == subType);
+
+                if (jsonDerivedTypeAttributes is { TypeDiscriminator: string discriminator })
+                {
+                    return discriminator;
+                }
+#endif
+
                 baseType = baseType.BaseType;
             }