Snowberry.Mediator.SourceGenerator 2.0.0

Snowberry.Mediator.SourceGenerator

A Roslyn incremental source generator for Snowberry.Mediator that discovers handlers, behaviors and notification handlers at compile time and emits the registration code with literal closed generics, eliminating all runtime reflection (Assembly.GetTypes(), Type.GetInterfaces(), MakeGenericType). The result is fully trim- and NativeAOT-friendly: no dynamic code is executed on the generated path.

Easy setup

1. Reference this package plus Snowberry.Mediator and a DI integration package (Snowberry.Mediator.Extensions.DependencyInjection for Microsoft.Extensions.DependencyInjection, or Snowberry.Mediator.DependencyInjection for the Snowberry container).

2. Add the opt-in attribute to your composition-root project (e.g. in Program.cs or an AssemblyInfo.cs):

   [assembly: SnowberryMediator]
   

3. Call the generated registration with no options.Assemblies and no hand-listed handler types:

   services.AddSnowberryMediator();                       // default Scoped lifetime
   services.AddSnowberryMediator(ServiceLifetime.Singleton);
   

Handlers are discovered both in your project and in referenced assemblies, as long as the composition-root project can access the type (public, or internal exposed via [InternalsVisibleTo]).

What is discovered

Types implementing any of the Snowberry.Mediator marker interfaces (IRequestHandler<,>, IStreamRequestHandler<,>, INotificationHandler<>, IPipelineBehavior<,>, IStreamPipelineBehavior<,>), including open-generic behaviors and open-generic notification handlers. Pipeline ordering via [PipelineOverwritePriority] is honored, with byte-identical semantics to the reflection-based path.

The [SnowberryMediator] attribute exposes per-category toggles (all default true): RegisterRequestHandlers, RegisterStreamRequestHandlers, RegisterNotificationHandlers, RegisterPipelineBehaviors, RegisterStreamPipelineBehaviors.

Scoping which assemblies are scanned

By default the generator scans the current assembly and every referenced assembly that references Snowberry.Mediator.Abstractions. To restrict discovery, set ScanReferencedAssemblies = false and name the referenced assemblies to include with one [assembly: SnowberryMediatorAssembly(typeof(AnyTypeInThatAssembly))] per assembly:

// Scan only this assembly plus the two named ones; ignore all other referenced handlers.
[assembly: SnowberryMediator(ScanReferencedAssemblies = false)]
[assembly: SnowberryMediatorAssembly(typeof(MyApp.Orders.PlaceOrderHandler))]
[assembly: SnowberryMediatorAssembly(typeof(MyApp.Billing.Marker))]

• The current (composition-root) assembly is always scanned because it carries the opt-in attribute.
• ScanReferencedAssemblies = true (the default) scans every eligible referenced assembly; SnowberryMediatorAssembly markers are ignored in that mode (everything is already scanned).
• Open-generic behaviors/handlers only close over request/notification types from scanned assemblies, so excluding an assembly removes both its handlers and its closure targets.

Use this to stop an unwanted referenced assembly's handlers from registering (surprise registrations, or SBMED001 duplicate-handler errors when two assemblies handle the same request).

Per-handler service lifetime

AddSnowberryMediator(lifetime) applies one lifetime to every discovered handler. To give a specific handler a different lifetime, register it before calling the generated entry point, because the generated registrations use no-overwrite (TryAdd) semantics, so a pre-registered handler keeps your lifetime:

services.AddSingleton<IRequestHandler<GetUser, string>, GetUserHandler>(); // your chosen lifetime
services.AddSnowberryMediator();                                           // skips the pre-registered one

Diagnostics