Final fixes

src/Elastic.Clients.Elasticsearch/_Generated/Api/IndexRequest.g.cs

@@ -168,10 +168,10 @@ public IndexRequest(Elastic.Clients.Elasticsearch.IndexName index) : base(r => r
 	{
 	}
 
-	//[JsonConstructor]
-	//internal IndexRequest()
-	//{
-	//}
+	[JsonConstructor]
+	public IndexRequest() : this(typeof(TDocument))
+	{
+	}
 
 	internal override ApiUrls ApiUrls => ApiUrlLookup.NoNamespaceIndex;
 
@@ -352,4 +352,4 @@ protected override void Serialize(Utf8JsonWriter writer, JsonSerializerOptions o
 	{
 		settings.SourceSerializer.Serialize(DocumentValue, writer);
 	}
-}
+}

src/Elastic.Clients.Elasticsearch/_Generated/Api/TermVectorsRequest.g.cs

@@ -202,7 +202,7 @@ public TermVectorsRequest(Elastic.Clients.Elasticsearch.IndexName index) : base(
 	}
 
 	[JsonConstructor]
-	internal TermVectorsRequest()
+	public TermVectorsRequest() : this(typeof(TDocument))
 	{
 	}
 

src/Elastic.Clients.Elasticsearch/_Shared/Api/IndexRequest.cs

@@ -10,9 +10,6 @@ namespace Elastic.Clients.Elasticsearch;
 
 public partial class IndexRequest<TDocument>
 {
-	[JsonConstructor]
-	public IndexRequest() : this(typeof(TDocument)) { }
-
 	public IndexRequest(TDocument document, Id id) : this(typeof(TDocument), id) => Document = document;
 
 	protected override HttpMethod? DynamicHttpMethod => GetHttpMethod(this);

src/Elastic.Clients.Elasticsearch/_Shared/Next/JsonUnionSelector.cs

@@ -0,0 +1,98 @@
+// Licensed to Elasticsearch B.V under one or more agreements.
+// Elasticsearch B.V licenses this file to you under the Apache 2.0 License.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Text.Json;
+
+namespace Elastic.Clients.Elasticsearch.Serialization;
+
+/// <summary>
+/// A delegate that selects a union variant (e.g. based on the current JSON token type).
+/// </summary>
+/// <param name="reader">A reference to a <see cref="Utf8JsonReader"/> instance.</param>
+/// <param name="options">The <see cref="JsonSerializerOptions"/> to use.</param>
+/// <returns>The selected <see cref="UnionTag"/> value.</returns>
+/// <remarks>
+/// IMPORTANT:
+/// The <see cref="Utf8JsonReader"/> is passed by reference for best performance. If the selector function
+/// implementation needs to advance the reader position, it must always operate on a copy of the original
+/// <paramref name="reader"/> or restore the reader state before returning.
+/// </remarks>
+internal delegate UnionTag JsonUnionSelectorFunc(ref Utf8JsonReader reader, JsonSerializerOptions options);
+
+[Flags]
+internal enum JsonTokenTypes
+{
+	None = 0,
+	StartObject = 1 << JsonTokenType.StartObject,
+	EndObject = 1 << JsonTokenType.EndObject,
+	StartArray = 1 << JsonTokenType.StartArray,
+	EndArray = 1 << JsonTokenType.EndArray,
+	String = 1 << JsonTokenType.String | 1 << JsonTokenType.PropertyName,
+	Number = 1 << JsonTokenType.Number,
+	True = 1 << JsonTokenType.True,
+	False = 1 << JsonTokenType.False
+}
+
+internal static class JsonUnionSelector
+{
+	public static UnionTag ByTokenType(ref Utf8JsonReader reader, JsonSerializerOptions options, JsonTokenTypes first, JsonTokenTypes second)
+	{
+		_ = reader;
+		_ = options;
+
+		if (((int)first & (1 << (int)reader.TokenType)) is not 0)
+		{
+			return UnionTag.T1;
+		}
+
+		if (((int)second & (1 << (int)reader.TokenType)) is not 0)
+		{
+			return UnionTag.T2;
+		}
+
+		return UnionTag.None;
+	}
+
+	public static UnionTag ByPropertyOfT1(ref Utf8JsonReader reader, JsonSerializerOptions options, string name)
+	{
+		reader.ValidateToken(JsonTokenType.StartObject);
+
+		var internalReader = reader;
+
+		while (internalReader.Read() && (internalReader.TokenType is JsonTokenType.PropertyName))
+		{
+			if (internalReader.ValueTextEquals(name))
+			{
+				return UnionTag.T1;
+			}
+
+			internalReader.Read();
+			internalReader.Skip();
+		}
+
+		return UnionTag.T2;
+	}
+
+	public static UnionTag ByPropertyOfT2(ref Utf8JsonReader reader, JsonSerializerOptions options, string name)
+	{
+		reader.ValidateToken(JsonTokenType.StartObject);
+
+		var internalReader = reader;
+
+		while (internalReader.Read() && (internalReader.TokenType is JsonTokenType.PropertyName))
+		{
+			if (internalReader.ValueTextEquals(name))
+			{
+				return UnionTag.T2;
+			}
+
+			internalReader.Read();
+			internalReader.Skip();
+		}
+
+		return UnionTag.T1;
+	}
+}