Description
Background and motivation
System.Text.Json does not currently have built-in support for Int128/UInt128 and Half.
API Proposal
namespace System.Text.Json.Serialization.Metadata;
public partial class JsonMetadataServices
{
public static JsonConverter<Int128> Int128Converter { get; }
public static JsonConverter<UInt128> UInt128Converter { get; }
public static JsonConverter<Half> HalfConverter { get; }
}API Usage
The JsonMetadataServices APIs are marked EditorBrowsable.Never and are only intended for use by the source generator.
Alternative Designs
Note that this proposes adding numeric type support on the converter level only and not on the Utf8JsonWriter/Utf8JsonReader types or the DOM types. Since the underlying types do not have support for large numbers representable in Int128 or BigInteger, we need to make use of other primitives. Examples of this can be found in this PR. Deserialization without incurring allocation also necessitates making this change.
Risks
Adding built-in support for new types risks regressing code size for apps that use both reflection and trimming such as Blazor. If folks think this is unacceptable, we might consider making these opt-in specifically for reflection, requiring users to manually touch the relevant converters:
var options = new JsonSerializerOptions { Converters = { JsonMetadataServices.BigIntegerConverter } };Although it goes without saying this would introduce inconsistent behavior between the two serializers.
Related to #86442