Improve compile-time checking for a case of passing instance's method as a callback

[Deilan]

TypeScript Version: 2.5.2

Repo with demo
Typescript Playground

Code

class Foo {
    private result: number = 42;

    public func(this: Foo): number {
        return this.result;
    }
}

function action(): void {
    console.log("Hello world!");
}

function bar(callbackFn: (this: void) => any, thisArg?: undefined): any;
function bar<T>(callbackFn: (this: T) => any, thisArg: T): any;
function bar<T, TResult>(callbackFn: (this: T) => TResult, thisArg: T): TResult {
    return callbackFn.call(thisArg);
}

const foo = new Foo();
const obj = new Object();

bar(action); // success - ok
bar(() => action()); // success - ok
bar(function() { return action(); }); // success - ok

bar(action, foo); // success - NOT ok, expected ERROR
bar(() => action(), foo); // success - NOT ok, expected ERROR
bar(function() { return action(); }, foo); // success - NOT ok, expected ERROR

bar(action, obj); // success - NOT ok, expected ERROR
bar(() => action(), obj); // success - NOT ok, expected ERROR
bar(function() { return action(); }, obj); // success - NOT ok, expected ERROR



bar(foo.func); // ERROR - ok
bar(() => foo.func()); // success - NOT ok, expected ERROR
bar(function() { return foo.func(); }); // success - NOT ok, expected ERROR

bar(foo.func, foo); // success - ok
bar(() => foo.func(), foo); // success - ok
bar(function() { return foo.func(); }, foo); // success - ok

bar(foo.func, obj); // success - ok
bar(() => foo.func(), obj); // success - ok
bar(function() { return foo.func(); }, obj); // success - ok



bar(obj.toString); // success - NOT ok, expected ERROR
bar(() => obj.toString()); // success - NOT ok, expected ERROR
bar(function() { return obj.toString(); }); // success - NOT ok, expected ERROR

bar(obj.toString, foo); // success - NOT ok, expected ERROR
bar(() => obj.toString(), foo); // success - NOT ok, expected ERROR
bar(function() { return obj.toString(); }, foo); // success - NOT ok, expected ERROR

bar(obj.toString, obj); // success - ok
bar(() => obj.toString(), obj); // success - ok
bar(function() { return obj.toString(); }, obj); // success - ok

Expected behavior:

bar(action, foo); // ERROR
bar(() => action(), foo); // ERROR
bar(function() { return action(); }, foo); // ERROR

bar(action, obj); // ERROR
bar(() => action(), obj); // ERROR
bar(function() { return action(); }, obj); // ERROR



bar(() => foo.func()); // ERROR
bar(function() { return foo.func(); }); // ERROR



bar(obj.toString); // ERROR
bar(() => obj.toString()); // ERROR
bar(function() { return obj.toString(); }); // ERROR

bar(obj.toString, foo); // ERROR
bar(() => obj.toString(), foo); // ERROR
bar(function() { return obj.toString(); }, foo); // ERROR

Actual behavior:

bar(action, foo); // success
bar(() => action(), foo); // success
bar(function() { return action(); }, foo); // success

bar(action, obj); // success
bar(() => action(), obj); // success
bar(function() { return action(); }, obj); // success



bar(() => foo.func()); // success
bar(function() { return foo.func(); }); // success



bar(obj.toString); // success
bar(() => obj.toString()); // success
bar(function() { return obj.toString(); }); // success

bar(obj.toString, foo); // success
bar(() => obj.toString(), foo); // success
bar(function() { return obj.toString(); }, foo); // success

[DanielRosenwasser]

Hey @Deilan thanks for putting this together, but this looks like a duplicate of #7968.

[mhegazy]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.