Object spreading produces wrong type with non-literal keys

🔎 Search Terms

object spread, object rest, object spreading

🕗 Version & Regression Information

• This is the behavior in every version I tried, and I reviewed the FAQ for entries about object spreading

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.2.2#code/CYUwxgNghgTiAEYD2A7AzgF0QLngb3gG0BrEAT10xgEsUBzAXVxQFcBbAIxBngF8BYAFDJ0WKLgIlylDDXpN4VWnT7wAvPiEBIcfADkegDTaAdGbBDeQA

💻 Code

declare const c: { [key: string]: number }
const a: { [key: string]: string } = {
	a: '',
	...c
}

🙁 Actual behavior

It allows numbers to be in the object, when they shouldn't be allowed.

🙂 Expected behavior

It shouldn't allow numbers.

Additional information about the issue

Because c has non-literal keys, in this case string, which could be any string, it doesn't care what's in it.

Start with the linked TypeScript Playground reproduction and verify the reported assignment is accepted. Trace how object spread with a non-literal string index key is typed, then confirm the fix rejects the number-valued spread in this example and add or update coverage for the behavior.