v5.7.1

Type inference bug fixes

This new release fixes the following bug in exhaustiveness checking when matching on optional properties:

type Input = { type?: 'one' } | { type: 'two' };

const f1 = (input: Input) =>
  match(input)
    .with({ type: 'one' }, () => {})
    .with({ type: 'two' }, () => {})
    .exhaustive(); // shouldn't type-check, but does 👎


const f2 = (input: Input) =>
  match(input)
    .with({ type: 'one' }, () => {})
    .with({ type: 'two' }, () => {})
    .with({ type: undefined }, () => {}) // <- the type key needs to be present.
    .exhaustive();  // shouldn't type-check, but does 👎

These two cases don't type check anymore. They fail with a NonExhaustiveError<{ type?: undefined; }>. To fix it, you should do:

type Input = { type?: 'one' } | { type: 'two' };

const f = (input: Input) =>
  match(input)
    .with({ type: 'one' }, () => {})
    .with({ type: 'two' }, () => {})
    .with({ type: P.optional(undefined) }, () => {}) // <- the type property may not be there
    .exhaustive(); // ✅

This is a purely type-level change, the runtime behavior is still the same.

What's Changed

• fix(.exhaustive): optional discriminant by @gvergnaud in #319

Full Changelog: v5.7.0...v5.7.1