redundantMapError

Suggests hoisting a repeated trailing Effect.mapError from every yield in an Effect generator

Property	Value
Category	Style
Default severity	suggestion
Fixable	No
Effect versions	v3, v4
Diagnostic codes	TS377088, TS377089
Language Service name	redundantMapError
Oxlint name	effecttsgo/redundant-map-error

Preview

import { Effect } from "effect"

declare const first: Effect.Effect<number, unknown>
declare const second: Effect.Effect<string, unknown>

class RepoError {
  constructor(readonly args: { cause: unknown }) {}
}

export const program = Effect.gen(function*() {
/**
                                  ^^^^^^^^^ effecttsgo(redundant-map-error): This generator applies the same inline `Effect.mapError(...)` to every yielded effect. Keep that `Effect.mapError(...)` inline and hoist it once to the generator result: `Effect.gen(...).pipe(Effect.mapError(...))`, or `Effect.fn(function*(){ ... }, Effect.mapError(...))`.
*/
  yield* first.pipe(
    Effect.mapError((cause) => new RepoError({ cause }))
  )

  return yield* second.pipe(
    Effect.mapError((cause) => new RepoError({ cause }))
  )
})

Language Service Configuration

See the Language Service setup guide for installation instructions.

{
  "$schema": "./node_modules/@effect/tsgo/schema.json",
  "compilerOptions": {
    "plugins": [
      {
        "name": "@effect/language-service",
        "diagnosticSeverity": {
          "redundantMapError": "warning"
        }
      }
    ]
  }
}

Oxlint Configuration

See the Oxlint setup guide for installation and patching instructions.

{
  "$schema": "./node_modules/@effect/tsgo/oxlint-schema.json",
  "options": {
    "typeAware": true
  },
  "plugins": ["effecttsgo"],
  "rules": {
    "effecttsgo/redundant-map-error": "warn"
  }
}