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oxlint-plugin-effect

no-effect-return-type

Intent: Effect, Stream and Layer return types are inferred, not annotated, except on exported declarations.

// ❌ no
(effect, name): Effect.Effect<RaceFillResult, never, Agent | SheetReader | SheetWriter> =>


// ✅ yes
(effect, name) =>


// ✅ yes: an exported declaration keeps its annotation as a contract
export const findPrice = (id: PriceId): Effect.Effect<Price, PriceNotFound> =>

Trigger: Effect.Effect, Stream.Stream or Layer.Layer in an annotated return type, even nested (Option.Option<Effect.Effect<…>>, a function returning an Effect).

Exemptions and blind spots: module-level declarations with export (export const, export function, export default), unless checkExported is on; methods of an exported object, functions an exported function returns, and export { f } lists are still checked. Recursion, and returns of different shapes that need unifying (Effect.succeed and Effect.fail), recognized from the shape of the returns. An import type { Effect } used as Effect<…> slips through.

Why: the error and requirement channels collect what comes from everything the function calls; an error or a service added deep down would change every caller’s annotation. An exported signature is the module’s contract, like a named type: there the annotation makes such a change visible where it is published. To check a returned object against a named type, annotate the callback that builds it (Effect.map(CurrentSession, (session): OrganizationContext => ({ … }))) or use satisfies.

Options:

  • checkExported: default false. Also checks exported declarations.

Fix: suggestion that removes the annotation