Class method with this typing cannot access private or protected members

[krryan]

TypeScript Version: 2.2.0-dev.20170116

Code

class Foo {
    constructor(
        protected bar: string | null,
        protected baz: number
    ) {}

    doThing(this: Foo & { bar: string }) {
        return this.bar.length > 0 ? this.baz : -1;
    }
}

Expected behavior:
Compiles without error.

Actual behavior:

Property 'baz' does not exist on type 'Foo & { bar: string; }`.

Notably, though, even if baz is public, attempting to use doThing here even from within another method fails:

class Foo {
    constructor(
        protected bar: string | null,
        public baz: number
    ) {}

    doThingIfYouCan() {
        if (this.bar != null) {
            return this.doThing(); // error here
        }
    }

    doThing(this: Foo & { bar: string }) {
        return this.bar.length > 0 ? this.baz : -1;
    }
}

Here the error is

The 'this' context of type 'this' is not assignable to method's 'this' of type 'Foo & { bar: string; }'.
[...]
Property 'bar' is protected in 'Foo' but public in type '{ bar: string; }'.

This is a very similar problem, where the this typing on doThing requires that bar is public even though both canDoThing and doThing should have access to it.

My use-case here is that I have a method that is currently only being called in non-null cases, and only makes sense to call in non-null cases, so I'm currently throwing in a null case (that should never happen). But I would like to enforce that at compile time.

[jakebailey]

This issue had the same root cause as #11454 and is now fixed in TS 3.9+ (see linked issue).