Parameters<T> and ReturnType<T> limitation

TypeScript Version: 3.9.2

Search Terms:
Generic Method Extend Parameters ReturnType

Code

export class Test {

    myMethod(): string {
        return "42";
    }

    myMethod2(a: string): string {
        return "42" + a;
    }

    //  Works  ---
    override<M extends keyof this>(method: M, newFunc: this[M]) {
    }

    //  Works  ---
    override2<M extends keyof this>(method: M, newFunc: (...args: Parameters<this["myMethod2"]>) => ReturnType<this["myMethod2"]>) {
    }

    //  Fails  ---
    override3<M extends keyof this>(method: M, newFunc: (...args: Parameters<this[M]>) => ReturnType<this[M]>) {
    }
}

const test = new Test();

test.override("myMethod2", a => "xxx");
test.override2("myMethod2", a => "xxx");
test.override3("myMethod2", a => "xxx");

Expected behavior:
I would expect override3 to compile and be equivalent to override + override2 (when M == "myMethod2")

Actual behavior:
override3 causes syntax error:

Type 'this[M]' does not satisfy the constraint '(...args: any) => any'.
  Type 'this[keyof this]' is not assignable to type '(...args: any) => any'.
    Type 'this[string] | this[number] | this[symbol]' is not assignable to type '(...args: any) => any'.
      Type 'this[string]' is not assignable to type '(...args: any) => any'.

Playground Link:
https://www.typescriptlang.org/play/?ssl=28&ssc=14&pln=28&pc=15#code/MYGwhgzhAEAqCmEAu0DeAod1vQLYE8BZeJACwHsATACgEoAuaZAJwEsA7AczSxz+ZIBXZu2gAiACwAmMQG5e2AL6Y+BYmSpTqYRiw6cGTJGy48+-ISPHSx0ANTQw8vsoXQA9O+wB1cswDWMNAAtKFu5ABu8MxslPAAPITQ8AAeSPDslDD+8PjkAGbQZKwQAHzUuCQUlIyEADTQ7PAA7gBiguzAjMUQANqEALq0ZjiufJ4+foHYocHhUTGscVKJyWkZWdA5eYU95ZUaNdD1jS3tnYzUAHQ3YMycEIwACndgB9EQ8T29YmpVmmIBqVhgBeUrQABKlnYsHwAAcEt9fkR-pQZEDhhgXCocBNoK0wKwQEFZvNorF4ABmVapdKZbK5ApFUglfao2oNJptDpdaDXW73R7QF7MN4kD5fFl9QbA6BgyHQ2EIyUlfoYkZKdCuYDkdjIIqIFAg07NOCGujydDpZBXSLkpbwajI9TVGQNMBy8FiFI+sS0eTWpC2hYUrTO1Fuxye8Q+lJ+gOG4P2uKUp1-Q6Rj3y72+-3oIA

Related Issues:

Commencez par la reproduction liée dans TypeScript Playground et examinez la manière dont le compilateur traite Parameters et ReturnType lorsque T est le générique indexé this[M]. L’issue est terminée lorsque l’exemple override3 se compile avec l’inférence attendue pour myMethod2 et que le comportement est couvert par un test approprié du compilateur.