No type mismatch for records with enum keys inside object literal with dynamic key

[droooney]

🔎 Search Terms

enum dynamic key record

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play/?ts=6.0.3#code/C4TwDgpgBAglC8UAKBDATsAligNgHgCUIBjAezQBM8BpCEAGigDsBXAWwCMI0A+HgbgBQg0JCi0QCKAHIU0qAB8ZHaUMFkmAZ2BQA5hGASpACgCUALnF0EPGXLUbtUFJbiIA3oKhQA2vsN0ZgC6ltLaaJhMutL0ggC+-EA

💻 Code

type A = Partial<Record<Key, number>>;

type Key = 'a' | 'b';

const getKey = (): Key => 'a';

const a: A = {
  [getKey()]: 'string',
};

🙁 Actual behavior

TS didn't report an error even though it should

🙂 Expected behavior

Error report about type mismatch inside the record field

Additional information about the issue

As far as I've investigated it doesn't happen when the key is not an enum (i.e. string). Also when the dynamic key is narrowed down to a single option the error does get reported. However, when there are at least 2 options no error is reported.

[MartinJohns]

Duplicate of #38663.

Note: there is no enum in your example. 'a' | 'b' is called a union type.