🔎 Search Terms

infer, keyof, string, interpolation, union, all keys, too big, too wide

🕗 Version & Regression Information

Syntax not supported before 4.7
Similar behavior on all versions upwards

⏯ Playground Link

https://www.typescriptlang.org/play?ts=5.3.3&ssl=6&ssc=1&pln=21&pc=47#code/PTAEEkDsDMFMCd4EtIHNQENQGtYE9QB3JAFwAsVNQBnE5NUFAYwHtJqlbZISAbAvEli8AJtVAkWLIkhGwqAV0hI2AWABQGkDTw8MAD1CQWJGgoAO5lvBKwRoAEaxo1+QBYAdAHYPbrWAcFdGh4FgBbCTIEeTVNdRI8c3kAEQAGUABeUABvDVBMAC5QAHJU4oAaPMci4oBGCqqmGoAmYo0AXwBuDQ0EpNBk2sycqowMGrLK9XyHGvqp-KaS1o7uuL75ABVYWgAeZIwSDHLQTYA+Yc3QWH1bSDFQAAMAEmyUOHhQAGlr2+4H3B4FjQAaHLAAMhodBQqHar1o9Fhj1AAH5vqAitAMLxqLA1r1Elt0lltns0idihgABo04pnTr5fLaSlteKE05DEk7Ej7WoUsY0ql0hlMsDFBzFAA+xSYUspGFZQA

💻 Code

type D0 = {
  a: '0',
  b: '1',
  c: '2'
};

type D1 = {
  aa: '0',
  b: '1',
  c: '2'
};

type Test<Data, T> = T extends `${infer K extends keyof Data & string}${string}` ? K : false;

type T0 = Test<D0, 'aXXX'>;    // 'a'
type T1 = Test<D1, 'aaXXX'>;   // 'b'|'c'|'aa'

🙁 Actual behavior

T1 is the union of all keys of D1 while only one fits within the pattern.
The extra keys are irrelevant.
The inference is not helpful.

This behavior seems inconsistent since T0 gives the expected key.

🙂 Expected behavior

T1 = 'aa'

Additional information about the issue

No response