#switch-exhaustiveness-check

#Configuration

import { defineConfig, ts } from '@rslint/core';

export default defineConfig([
  ts.configs.recommended,
  {
    rules: {
      '@typescript-eslint/switch-exhaustiveness-check': 'error',
    },
  },
]);

#Rule Details

Require switch statements over union types to be exhaustive. When switching over a union type (such as a discriminated union or enum), it is easy to forget to handle all possible cases. This rule ensures that every possible value of the union is handled with a case clause, either explicitly or via a default clause, preventing runtime errors from unhandled values.

Examples of incorrect code for this rule:

type Direction = 'north' | 'south' | 'east' | 'west';

function move(dir: Direction) {
  switch (dir) {
    case 'north':
      break;
    case 'south':
      break;
    // 'east' and 'west' are not handled
  }
}

Examples of correct code for this rule:

type Direction = 'north' | 'south' | 'east' | 'west';

function move(dir: Direction) {
  switch (dir) {
    case 'north':
      break;
    case 'south':
      break;
    case 'east':
      break;
    case 'west':
      break;
  }
}

#Options

#allowDefaultCaseForExhaustiveSwitch

If false, a default clause is reported as unnecessary once every member of the union already has its own case.

{ "switch-exhaustiveness-check": ["error", { "allowDefaultCaseForExhaustiveSwitch": false }] }

type Direction = 'north' | 'south';

function move(dir: Direction) {
  switch (dir) {
    case 'north':
      break;
    case 'south':
      break;
    default:
      break;
  }
}

#requireDefaultForNonUnion

If true, also requires a default clause for switches over non-union types (such as number or string), so they are held to the same standard as unions.

{ "switch-exhaustiveness-check": ["error", { "requireDefaultForNonUnion": true }] }

declare const value: number;

switch (value) {
  case 0:
    break;
  case 1:
    break;
}

#considerDefaultExhaustiveForUnions

If true, a default clause on a switch over a union type is itself treated as covering every unhandled member, instead of requiring each member to have an explicit case.

{ "switch-exhaustiveness-check": ["error", { "considerDefaultExhaustiveForUnions": true }] }

type Direction = 'north' | 'south';

function move(dir: Direction) {
  switch (dir) {
    case 'north':
      break;
    default:
      break;
  }
}

#defaultCaseCommentPattern

Regular expression for a trailing comment that stands in for a missing default clause. Defaults to /^no default$/i.

{ "switch-exhaustiveness-check": ["error", { "defaultCaseCommentPattern": "^skip default" }] }

declare const value: 'a' | 'b';

switch (value) {
  case 'a':
    break;
  // skip default
}

#Differences from ESLint

• When a switch is missing more than one case, the order of the types listed in the missingBranches message and the order the fixer inserts the corresponding case clauses follow rslint's internal type ordering rather than the union's declaration order. For example, type Day = 'Monday' | 'Tuesday' | 'Wednesday' reports missing cases as "Monday" | "Tuesday" | "Wednesday", alphabetized, even when the type alias declares them in a different order.

#Original Documentation

• typescript-eslint: switch-exhaustiveness-check
• Source code