Union in a computed property allows any assignment to property value

TypeScript Version: 4.0.0-dev.20200518

Search Terms: computed property, union

Code

type Key = 'a' | 'b';

const index1: Record<Key, string> = { a: '', b: 0 }; // Errors as expected, ok
const index2: Record<Key, string> = { a: '', b: '' };

const b: Key = 'b';

const index3: Record<Key, string> = { ...index2, [b]: 0 }; // Errors as expected, ok

declare var k: Key;

// No errors, allowing anything to be assigned to string
const index4: Record<Key, string> = { ...index2, [k]: [] };
const index5: Record<Key, string> = { a: '', b: '', [k]: 0 };

Expected behavior:
Expected error for invalid assignments in index4 and index5.

Actual behavior:
No error, allowing anything to be assigned to string

Playground Link: here

Related Issues:
https://github.com/microsoft/TypeScript/issues/36920: perhaps the computed property is deemed an excess property, though I don't think it should be

Commencez par exécuter la reproduction fournie dans Playground et comparez les diagnostics pour index4 et index5 avec les erreurs attendues. Examinez la gestion des propriétés calculées et la vérification des propriétés excédentaires, notamment l’issue associée #36920 ; le travail est terminé lorsque les deux affectations invalides sont rejetées sans régression pour les exemples valides.