Fix json serialization of geometries

sdk/core/Azure.Core.Experimental/api/Azure.Core.Experimental.netstandard2.0.cs

@@ -50,7 +50,7 @@ public CollectionGeometry(System.Collections.Generic.IEnumerable<Azure.Core.Spat
         public CollectionGeometry(System.Collections.Generic.IEnumerable<Azure.Core.Spatial.Geometry> geometries, Azure.Core.Spatial.GeometryProperties properties) : base (default(Azure.Core.Spatial.GeometryProperties)) { }
         public System.Collections.Generic.IReadOnlyList<Azure.Core.Spatial.Geometry> Geometries { get { throw null; } }
     }
-    public partial class Geometry
+    public abstract partial class Geometry
     {
         protected Geometry(Azure.Core.Spatial.GeometryProperties properties) { }
         public Azure.Core.Spatial.GeometryProperties Properties { get { throw null; } }
@@ -74,6 +74,7 @@ protected Geometry(Azure.Core.Spatial.GeometryProperties properties) { }
     public partial class GeometryJsonConverter : System.Text.Json.Serialization.JsonConverter<Azure.Core.Spatial.Geometry>
     {
         public GeometryJsonConverter() { }
+        public override bool CanConvert(System.Type typeToConvert) { throw null; }
         public override Azure.Core.Spatial.Geometry Read(ref System.Text.Json.Utf8JsonReader reader, System.Type typeToConvert, System.Text.Json.JsonSerializerOptions options) { throw null; }
         public override void Write(System.Text.Json.Utf8JsonWriter writer, Azure.Core.Spatial.Geometry value, System.Text.Json.JsonSerializerOptions options) { }
     }

sdk/core/Azure.Core.Experimental/src/Spatial/Geometry.cs

@@ -6,7 +6,7 @@ namespace Azure.Core.Spatial
     /// <summary>
     /// A base type for all spatial types.
     /// </summary>
-    public class Geometry
+    public abstract class Geometry
     {
         internal static readonly GeometryProperties DefaultProperties = new GeometryProperties();
 

sdk/core/Azure.Core.Experimental/src/Spatial/GeometryJsonConverter.cs

@@ -25,6 +25,12 @@ public class GeometryJsonConverter : JsonConverter<Geometry>
         private const string CoordinatesProperty = "coordinates";
         private const string BBoxProperty = "bbox";
 
+        /// <inheritdoc />
+        public override bool CanConvert(Type typeToConvert)
+        {
+            return typeof(Geometry).IsAssignableFrom(typeToConvert);
+        }
+
         /// <inheritdoc />
         public override Geometry Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
         {

sdk/core/Azure.Core.Experimental/tests/SpatialTests.cs

@@ -247,7 +247,20 @@ private T AssertRoundtrip<T>(string json) where T: Geometry
             var element2 = JsonDocument.Parse(memoryStreamOutput.ToArray()).RootElement;
             var geometry2 = GeometryJsonConverter.Read(element2);
 
-            return (T)geometry2;
+            var options = new JsonSerializerOptions()
+            {
+                Converters = { new GeometryJsonConverter() }
+            };
+
+            // Serialize and deserialize as a base class
+            var bytes = JsonSerializer.SerializeToUtf8Bytes(geometry2, typeof(Geometry), options);
+            var geometry3 = JsonSerializer.Deserialize<Geometry>(bytes, options);
+
+            // Serialize and deserialize as a concrete class
+            var bytes2 = JsonSerializer.SerializeToUtf8Bytes(geometry3, options);
+            var geometry4 = JsonSerializer.Deserialize<T>(bytes2, options);
+
+            return geometry4;
         }
     }
 }