GH-990: source generator infers a handler's emitted events into an assembly manifest

[jeremydmiller]

Closes #990.

Summary

Pass 2 bug fix. The syntax filter now admits any method with an attributed parameter, and the IRefersToAggregate check decides. Before this, [WriteModel] / [ReadModel] / [DcbModel] and user aliases never reached the semantic check.

New JasperFx.Events types

• ICarriesEvents: a marker interface for return types that carry events without naming them.
• EmittedEventsAttribute(Type handlerType, string methodName, params Type[] eventTypes): assembly-level, and allows multiple applications so a double-loaded analyzer doesn't fail the build.

New generator pass (EmittedEventsAnalyzer.cs)

• Candidates: a method taking an IEventStream<T> parameter or an IRefersToAggregate-attributed parameter, or returning an ICarriesEvents type. That includes tuple elements and looks inside Task<T>/ValueTask<T>.
• Collected from: AppendOne/AppendMany; constructors and static factories returning an ICarriesEvents type; collection initializers; Add-style calls on an ICarriesEvents value.
• Event slots: only arguments passed to parameters typed object, object[] or IEnumerable<object> count, so a Guid or string stream id is never mistaken for an event, wherever it sits.
• Skipped silently: object-typed values, anonymous types, and types a typeof at assembly scope can't name.
• Output: one JasperFxEmittedEvents.g.cs, emitted only when the compilation can see EmittedEventsAttribute. Each method's result is compared by value, so unrelated edits stay cached.

Decisions worth a look

• Overloads: the manifest is keyed on method name, so overloads of one method merge into one entry.
• Name matching: methods that add to an ICarriesEvents value are matched by name (Add, AddRange, Insert, InsertRange, Append, AppendOne, AppendMany). Matching on parameter shape alone would also pick up Contains(object).
• Abstract base types: a value typed as an abstract base event is recorded under that base type. Only object is excluded.

Tests

EmittedEventsManifestTests.cs covers:

• every case listed in the issue;
• no manifest when JasperFx.Events isn't referenced;
• incrementality, using Roslyn's step tracking;
• the pass 2 regression, which fails against the old name filter.

All 96 source generator tests pass, and jasperfx.slnx builds with 0 errors.

Wolverine follow-up: JasperFx/wolverine#4914.

🤖 Generated with Claude Code

https://claude.ai/code/session_01J8KxC18Q51z5w4u6YARwe4