Shiny Serialization

Shiny Serialization Skill

You are an expert in Shiny.Extensions.Serialization, a .NET library providing a centralized, AOT-safe JSON serializer with source-generated chaining of JsonSerializerContexts and collection wrappers.

When to Use This Skill

Invoke this skill when the user wants to:

• Replace ad-hoc JsonSerializer.Serialize/Deserialize calls with a centralized ISerializer
• Make multiple library-owned JsonSerializerContexts compose without manual services.AddJsonContext(...) calls
• Add AOT-safe List<T>, T[], or IEnumerable<T> support for a type whose element-level JsonTypeInfo is already source-generated (the "inline [JsonConverter] works, but List<T> throws" case)
• Provide a static serializer accessor that's usable before DI exists (e.g. mobile cold-start through Shiny.Stores)

Library Overview

Documentation: https://shinylib.net/serialization/ Repository: https://github.com/shinyorg/extensions Package: Shiny.Extensions.Serialization

Shiny.Extensions.Serialization ships a runtime + Roslyn source generator. The runtime owns one shared JsonSerializerOptions whose TypeInfoResolverChain collects every contributed JsonSerializerContext and custom resolver. The generator emits [ModuleInitializer]s that auto-register user contexts at load time, and AOT-safe collection wrappers for opted-in types.

Core Pieces

Setup

// DI (optional — Shiny.Json.Default works without it)
services.AddJsonSerialization();

That's it for DI. The generator does the rest by reading [ShinyJsonContext]/[ShinyJsonInclude] markers in your source.

Auto-registering a hand-written context

The recommended path. Decorate any normal STJ source-generator context with [Shiny.ShinyJsonContext]:

using System.Text.Json.Serialization;
using Shiny;

[ShinyJsonContext]
[JsonSerializable(typeof(MyDto))]
[JsonSerializable(typeof(MyOtherDto))]
internal partial class MyAppJsonContext : JsonSerializerContext;

The Shiny generator emits (in a hidden file):

[ModuleInitializer]
internal static void Init() => global::Shiny.Json.AddContext(MyAppJsonContext.Default);

The context registers before Main runs, so the static Shiny.Json.Default and any DI-resolved ISerializer both see the types. You do not need services.AddJsonContext(MyAppJsonContext.Default) anywhere.

Adding collection support

If an element type has JsonTypeInfo (from some context — auto-registered, hand-written + AddJsonContext, or anything else in the chain) but List<T>/T[] throw "no metadata" under AOT, mark the element type:

[ShinyJsonInclude]
public partial class MyDto
{
    public string Name { get; set; } = "";
}

Or, for a foreign type you don't own:

[assembly: Shiny.ShinyJsonInclude(typeof(SomeExternal.Vendor.Payload))]

The generator emits an IJsonTypeInfoResolver providing JsonTypeInfo<List<MyDto>>, JsonTypeInfo<MyDto[]>, JsonTypeInfo<IEnumerable<MyDto>>, JsonTypeInfo<IReadOnlyList<MyDto>>, JsonTypeInfo<IList<MyDto>>, JsonTypeInfo<ICollection<MyDto>>, and JsonTypeInfo<IAsyncEnumerable<MyDto>>. Each one lazy-resolves the element JsonTypeInfo<MyDto> from the chain at runtime — composes with any context that supplies it.

Composing with Inline JsonConverter<T>

This is the original mediator pain point. A type carrying [JsonConverter(typeof(MyConverter))] serializes fine in isolation, but List<MyType> throws under AOT because STJ has no JsonTypeInfo<List<MyType>>. Fix:

[ShinyJsonInclude]
[JsonConverter(typeof(BoxedIntConverter))]
public partial class BoxedInt { public int Value { get; set; } }

Now BoxedInt is serialized through the inline converter (bare number, not an object) AND List<BoxedInt>, BoxedInt[], etc. go through the generator-emitted collection wrappers. The wrappers lazy-fetch the element JsonTypeInfo which carries the inline converter — composition works.

DI Patterns

// Inject ISerializer anywhere
public class MyService(ISerializer serializer)
{
    public string Save(MyDto d) => serializer.Serialize(d);
    public MyDto Load(string j) => serializer.Deserialize<MyDto>(j);
}

// Mutate options before first use
services.ConfigureJsonSerializer(opts => opts.WriteIndented = false);

// Hand-add a context (for cases where you can't or won't decorate it with [ShinyJsonContext])
services.AddJsonContext(ThirdPartyJsonContext.Default);

Static Patterns

// Anywhere — no DI needed
var json = Shiny.Json.Default.Serialize(new MyDto { Name = "x" });
var back = Shiny.Json.Default.Deserialize<MyDto>(json);

// Late additions (before first Serialize call)
Shiny.Json.Configure(o => o.WriteIndented = false);
Shiny.Json.AddContext(SomeOtherContext.Default);

Diagnostics

Replacing the Serializer Wholesale

For non-JSON payloads (MessagePack, MemoryPack, etc.), swap the whole ISerializer:

// Simple — pre-built instance
services.AddSerializer(new MyMessagePackSerializer());

// DI-constructed
services.AddSerializer<MyConfiguredSerializer>();
host.Services.UseSerializer();   // call after Build() to snapshot into Shiny.Json.Default

UseSerializer() mirrors UseShinyStores() — needed when the custom ISerializer takes DI dependencies.

Tests

[Collection("ShinyJson")]
public class MyTests
{
    [Fact]
    public void Foo()
    {
        using var scope = Shiny.Json.CreateTestScope(
            extraResolvers: [ExtraContext.Default],
            extraConfigure: o => o.WriteIndented = false
        );
        // Scope disposes → registry trims back, cached serializer reset.
    }
}

Tests touching Shiny.Json must share an xUnit collection ([Collection("ShinyJson")]) because the registry is process-static.

Best Practices

1. [ShinyJsonContext] over manual AddJsonContext — module-init registration avoids "I forgot to call services.AddJsonContext(...) in this code path" bugs (which is exactly the latent bug we just patched in Shiny Locations GPS).
2. [ShinyJsonInclude] per element type, not per collection — never use [assembly: ShinyJsonInclude(typeof(List<Foo>))]. The generator already emits all the standard collection shapes from the element type.
3. Pair [ShinyJsonInclude] with a [JsonSerializable(typeof(T))] in the same assembly to silence SJSON003. If the element is registered in another assembly, suppress or accept the warning.
4. Don't put [ShinyJsonContext] on a context owned by another package — decorate types in your own code, not someone else's. For 3rd-party contexts you don't own, fall back to services.AddJsonContext(ThirdPartyContext.Default).
5. Shiny.Json.Configure runs before first use only. Once Default has been touched, JsonSerializerOptions freezes. Configure calls after that mutate the same options instance and may throw on certain properties — call early or wrap in CreateTestScope.