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

Reproduisez le diagnostic de l’exemple TypeScript Playground lié, puis suivez la vérification des contraintes génériques pour les types mappés avec des propriétés facultatives et des intersected keyof keys. Le travail est terminé lorsque l’exemple se compile sans erreur tout en préservant la vérification correcte des contraintes pour les cas associés.