typescript-exhaustive-switch

name	typescript-exhaustive-switch
description	Require exhaustive switch handling over TypeScript discriminated unions and enums by adding a `never` check in the default case. Apply when writing or reviewing a `switch` over a union or enum, and when adding a new variant to an existing union or enum.
paths	["**/*.ts","**/*.tsx"]

Exhaustive switch handling

In switch statements over discriminated unions or enums, use a never check in the default case so newly added variants cause compile-time failures until handled.

Pattern

switch (event.kind) {
  case "created":
    return handleCreated(event);
  case "deleted":
    return handleDeleted(event);
  default: {
    const unhandled: never = event;
    throw new Error(`Unhandled variant: ${JSON.stringify(unhandled)}`);
  }
}

The const unhandled: never assignment is the whole point: once a new variant is added to the union or enum, that assignment stops type-checking and the compiler points at every switch that has not been updated.

Rules

• Every switch over a discriminated union or enum gets the never default.
• Do not use a permissive default that silently swallows unknown variants — that turns a compile-time error into a runtime surprise.
• The same applies to exhaustive if/else if chains over a discriminant: end with a never-typed binding rather than a bare else.

When reviewing

If a new variant is added to a union or enum, check that every switch over it was updated. A switch without the never default is the reason such a variant can be missed, so flag it even when the current code happens to be complete.