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Sarj Code Standards

require-assert-never

Require a never witness in empty switch defaults so discriminated unions remain exhaustive at compile time.

missingAssertNever Rule source Tests Catalog JSON

Why

An empty default silently accepts new union members instead of making the compiler identify the missing case.

Fix

Use void (value satisfies never) or a helper accepting never, preserving the intended runtime fallback.

Examples

Before — flagged Do not leave an exhaustive default empty
src/render.ts
declare const kind: "a" | "b";
switch (kind) {
  case "a":
    break;
  case "b":
    break;
  default:
}
After — preferred Make the default exhaustive
src/render.ts
function assertNever(value: never): never {
  throw new Error(`Unexpected kind: ${String(value)}`);
}
declare const kind: "a" | "b";
switch (kind) {
  case "a":
    break;
  case "b":
    break;
  default:
    assertNever(kind);
}