swc/crates/swc_ecma_parser/tests/tsc/subtypingWithNumericIndexer.ts

// Derived type indexer must be subtype of base type indexer

interface Base { foo: string; }
interface Derived extends Base { bar: string; }
interface Derived2 extends Derived { baz: string; }

class A {
    [x: number]: Base;
}

class B extends A {
    [x: number]: Derived; // ok
}

class B2 extends A {
    [x: number]: Derived2; // ok
}

module Generics {
    class A<T extends Base> {
        [x: number]: T;
    }

    class B extends A<Base> {
        [x: number]: Derived; // ok
    }

    class B2 extends A<Base> {
        [x: number]: Derived2; // ok
    }

    class B3<T extends Base> extends A<T> {
        [x: number]: Derived; // error, BUG?
    }

    class B4<T extends Base> extends A<T> {
        [x: number]: Derived2; // error, BUG?
    }
}