Deserialize boolean strings to dynamic mapping (#4127)

This commit introduces a custom formatter for Union<bool,DynamicMapping>. A boolean value may be returned as a "true" or "false" string, which should be handled correctly.

Closes #4124

Author: russcam

src/Nest/Mapping/DynamicMapping.cs

@@ -1,5 +1,7 @@
 using System.Runtime.Serialization;
 using Elasticsearch.Net;
+using Elasticsearch.Net.Utf8Json;
+using Elasticsearch.Net.Utf8Json.Internal;
 
 
 namespace Nest
@@ -13,4 +15,60 @@ public enum DynamicMapping
 		[EnumMember(Value = "strict")]
 		Strict
 	}
+
+	internal class DynamicMappingFormatter : IJsonFormatter<Union<bool,DynamicMapping>>
+	{
+		private static readonly AutomataDictionary Values = new AutomataDictionary { { "true", 0 }, { "false", 1 }, { "strict", 2 } };
+
+		public void Serialize(ref JsonWriter writer, Union<bool, DynamicMapping> value, IJsonFormatterResolver formatterResolver)
+		{
+			if (value == null)
+			{
+				writer.WriteNull();
+				return;
+			}
+
+			switch (value.Tag)
+			{
+				case 0:
+					writer.WriteBoolean(value.Item1);
+					break;
+				case 1:
+					writer.WriteString(value.Item2.GetStringValue());
+					break;
+			}
+		}
+
+		public Union<bool, DynamicMapping> Deserialize(ref JsonReader reader, IJsonFormatterResolver formatterResolver)
+		{
+			if (reader.ReadIsNull())
+				return null;
+
+			var token = reader.GetCurrentJsonToken();
+			switch (token)
+			{
+				case JsonToken.True:
+				case JsonToken.False:
+					return new Union<bool, DynamicMapping>(reader.ReadBoolean());
+				case JsonToken.String:
+					var segment = reader.ReadStringSegmentUnsafe();
+					if (Values.TryGetValue(segment, out var value))
+					{
+						switch (value)
+						{
+							case 0:
+								return new Union<bool, DynamicMapping>(true);
+							case 1:
+								return new Union<bool, DynamicMapping>(false);
+							case 2:
+								return new Union<bool, DynamicMapping>(DynamicMapping.Strict);
+						}
+					}
+
+					return null;
+				default:
+					throw new JsonParsingException($"Cannot parse Union<bool, DynamicMapping> from token '{token}'");
+			}
+		}
+	}
 }

src/Nest/Mapping/TypeMapping.cs

@@ -27,6 +27,7 @@ public interface ITypeMapping
 		/// will result in an error if an unknown field is encountered in a document.
 		/// </summary>
 		[DataMember(Name = "dynamic")]
+		[JsonFormatter(typeof(DynamicMappingFormatter))]
 		Union<bool, DynamicMapping> Dynamic { get; set; }
 
 		/// <summary>

src/Nest/Mapping/Types/Complex/Object/ObjectProperty.cs

@@ -16,6 +16,7 @@ public interface IObjectProperty : ICoreProperty
 		/// Default is <c>true</c>
 		/// </summary>
 		[DataMember(Name = "dynamic")]
+		[JsonFormatter(typeof(DynamicMappingFormatter))]
 		Union<bool, DynamicMapping> Dynamic { get; set; }
 
 		/// <summary>

src/Tests/Tests.Core/ManagedElasticsearch/NodeSeeders/DefaultSeeder.cs

@@ -227,6 +227,7 @@ public static ITypeMapping ProjectTypeMappings(TypeMappingDescriptor<Project> m)
 					.AutoMap()
 					.Name(p => p.Committer)
 					.Properties(DeveloperProperties)
+					.Dynamic()
 				)
 				.Text(t => t
 					.Name(p => p.ProjectName)