JSon Wrapper Source Generator

What

This source generator takes interfaces decorated with the [JsonWrapper] attribute and generates an extension method and wrapper class to allow accesing items in a strongly typed fashion directly out of the JsonElement without deserializing.

Example

Given an interface like:

[JsonWrapper]
interface IPerson
{
    string FirstName { get; }
    string LastName { get; }
    int Age { get; }

This source generator would generate an AsIPerson() extension method on System.Text.Json.JsonElement and an implementation of IPerson that wraps the JsonElement and extracts each property on access.

Why?

This explores an idea of reducing the conversions and DTO types necessary for implementing Json HTTP APIs. Also, I haven't ever really looked at implementing a source generator, so I thought I'd give it a go.

Future ideas

1. Handle unwrapping array properties
2. Handle Nullable<T> properties.
3. Handle a few more basic values System.Text.Json.JsonElement has accessors for (eg Guid, DateTimeOffset, Base64Bytes)
4. Support properties that are themselves interfaces with [JsonWrapper] so that you can have a hierarchy.