Cannot override method in subclass when superclass instance type is a mapped type

TypeScript Version: 3.1.1

Search Terms:
defines instance member property

Code

class A {
    foo(): void {};
    bar: number;
}

class B extends (A as { new(): Pick<A, Exclude<keyof A, "foo">> & Pick<A, "foo"> }) {
    // (1)
    foo(): void {
        super.foo();
    }
    baz: number;
}

Expected behavior:
Compiles successfully

Actual behavior:

Error at (1): [ts] Class 'Pick<A, "bar"> & Pick<A, "foo">' defines instance member property 'foo', but extended class 'B' defines it as instance member function.

Playground Link: http://www.typescriptlang.org/play/index.html#src=class%20A%20%7B%0D%0A%20%20%20%20foo()%3A%20void%20%7B%7D%3B%0D%0A%20%20%20%20bar%3A%20number%3B%0D%0A%7D%0D%0A%0D%0Aclass%20B%20extends%20(A%20as%20%7B%20new()%3A%20Pick%3CA%2C%20Exclude%3Ckeyof%20A%2C%20%22foo%22%3E%3E%20%26%20Pick%3CA%2C%20%22foo%22%3E%20%7D)%20%7B%0D%0A%20%20%20%20foo()%3A%20void%20%7B%0D%0A%20%20%20%20%20%20%20%20super.foo()%3B%0D%0A%20%20%20%20%7D%0D%0A%20%20%20%20baz%3A%20number%3B%0D%0A%7D

A more realistic example of this is when using https://github.com/bterlson/strict-event-emitter-types along with subclassing a superclass with overridable methods:

import StrictEventEmitter from "strict-event-emitter-types";
import * as inspector from "inspector";

interface SessionEvents {
  "Runtime.executionContextCreated": (message: inspector.InspectorNotification<Runtime.ExecutionContextCreatedEventDataType>) => void
}
type StrictSession = StrictEventEmitter<inspector.Session, SessionEvents>;
class CustomSession extends (inspector.Session as { new (): StrictSession }) {
  connect() { // error here
    super.connect();
  }
}

Inizia con l’esempio di codice TypeScript e il link a Playground per riprodurre la diagnostica che coinvolge Pick, Exclude e l’override della sottoclasse. Traccia il modo in cui il compilatore confronta il membro della superclasse mappata con B.foo, quindi aggiungi la copertura per l’esempio e conferma che l’override valido venga compilato senza errori.