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CHR0054: Reactor method has an unsupported return type

Rule description

Section titled “Rule description”

A reactor method whose first parameter is an [EventType] but whose synchronous return type is neither a built-in supported shape nor claimed by a registered side-effect handler is skipped during handler discovery. CHR0054 reports return types the analyzer cannot recognize, rather than treating them as unresolvable parameters.

Severity

Section titled “Severity”

Warning

Supported returns

Section titled “Supported returns”
  • void or Task.
  • A registered event type, EventForEventSourceId, or EventsWithConcurrencyScopes.
  • A custom type marked [ReactorSideEffect] from Cratis.Chronicle.Reactors.SideEffects, including types deriving from a marked base class or implementing a marked interface.
  • A one-dimensional array or IEnumerable<T> implementation where T is a registered event type, EventForEventSourceId, object (for mixed events and targeted events), or a marked side-effect type.
  • Task<T> for any side effect that a registered reactor side-effect handler can process, including the shapes above.

Synchronous custom side effects require a registered IReactorSideEffectHandler whose CanHandleReturnType(Type) claims the declared return type and which processes the returned value. Mark the custom type [ReactorSideEffect] so the analyzer accepts it; the marker only informs the analyzer and registers nothing. For a collection return, the handler must claim and process the collection type, not only its elements. See Custom return type handlers.

Section titled “Related rules”
  • CHR0004: Reactor method has a parameter that cannot be resolved.
  • CHR0005: Reactor event parameter must have [EventType] attribute.

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