Skip to content

Omnibus fresh object subtype reduction / contextual type issue #19236

Closed
@RyanCavanaugh

Description

@RyanCavanaugh
// Problem 1: Error spans are useless in contextually-typed array/object literal cases
type Kind = 'foo' | 'ball';
// Error is on declared identifier instead of bad element
const ka: Kind[] = [
    'foo', 'ball', 'xxxx', 'foo', 'ball'
];
// Error is on declared identifier instead of bad key
const ko: { [s: string]: Kind } = {
    'x': 'foo',
    'y': 'xxxx',
    'z': 'foo'
};

// Problem 2: Subtype reduction screwage in the presence of contextual type
type OK = { ok?: boolean };
// No error??
const o1: OK = '??' ? { ok: 'wat' } : { };

// Problem 3: Aliased subtype reduction screwage
const obj = '??' ? { ok: 'wat' } : {};
// No error??
const o2: OK = obj;

Hypotheses:

  • Computing a union type in the presence of a contextual type is a waste of time
    • If we do this, we can produce good error spans?
  • Unioning { x: T } with a fresh { } should produce { x?: T }
  • Unioning a fresh object literal with { } should do something special
  • Unioning fresh { x: number, y: number } | { x: number } should produce { x: number, y?: number}

Metadata

Metadata

Assignees

Labels

FixedA PR has been merged for this issueSuggestionAn idea for TypeScript

Type

No type

Projects

No projects

Relationships

None yet

Development

No branches or pull requests

Issue actions