Type argument with a subset of the parameter constraint's optional keys incorrectly reported as unassignable to constraint

🔎 Search Terms

"does not satisfy the constraint" "keyof" "optional"

🕗 Version & Regression Information

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

⏯ Playground Link

https://www.typescriptlang.org/play/?#code/C4TwDgpgBAsiAq4IB54BooFUoQB7AgDsATAZygG8oBtAaSgEtCoBrCEAewDMp4BdAPwAuKAFdCLQhwDuzAL4A+KAF4sAbgCwAKG0BjADYBDUuTgBhIydRKK2qFABuh-aIgBCEXESRUGKnUZmNk4eeCgAMihSYAAnJgBzQRFxSRl5BU0tOW0gA

💻 Code

type MyType<T, U extends { [K in keyof T]?: unknown }> = U;

class MyClass<T> {
  value!: MyType<T, { [K in keyof T & string]?: unknown }>;
}

🙁 Actual behavior

The following error is reported:

Type '{ [K in keyof T & string]?: unknown; }' does not satisfy the constraint '{ [K in keyof T]?: unknown; }'.
  Type 'keyof T' is not assignable to type 'keyof T & string'.
    Type 'string | number | symbol' is not assignable to type 'keyof T & string'.
      Type 'string' is not assignable to type 'keyof T & string'.
        Type 'string' is not assignable to type 'keyof T'.
          Type 'keyof T' is not assignable to type 'string'.
            Type 'string | number | symbol' is not assignable to type 'string'.
              Type 'number' is not assignable to type 'string'.

🙂 Expected behavior

No error should be reported because due to the keys being optional, { [K in keyof T & string]?: unknown } is a subtype of { [K in keyof T]?: unknown } for all T.

Additional information about the issue

No response

Reproduziere die Diagnose aus dem verlinkten TypeScript Playground-Beispiel und verfolge anschließend die Prüfung generischer Constraints für gemappte Typen mit optionalen Eigenschaften und intersected keyof keys. Die Arbeit ist abgeschlossen, wenn das Beispiel ohne Fehler kompiliert und gleichzeitig die korrekte Constraint-Prüfung für verwandte Fälle erhalten bleibt.