control flow with instanceof not works properly

[emilgpa]

TypeScript Version:

nightly (1.9.0-dev.20160429)

Code

class AAA {
    fieldA: string;
}

class BBB {
    fieldB: string;
}

class AA {
    data: AAA;
}

class BB {
    data: BBB;
}

class A {
    d: AA;
}

class B {
    d: BB;
}

function main(x: A | B) {
    for (let i of [1, 1]) {
        if (x instanceof A) {
            x.d.data.fieldA;
        } else if (x instanceof B) {
            x.d.data.fieldB; // Not compiles here. 
        }
    }
}

Expected behavior:

To access to the fieldB field of BBB class inside of block } else if (x instanceof B) {

Actual behavior:

The compiler raises the follow error: TS2339: Property 'fieldB' does not exist on type 'AAA'..
The behavior in the version 1.8.10 is correct.

[malibuzios]

I tried to reduce the example to the simplest one possible, that still errored:

class A {
    prop: { a: string; };
}

class B {
    prop: { b: string; }
}

declare let x: A | B;

while (true) {
    if (x instanceof A) {
        x.prop.a;
    } else if (x instanceof B) {
        x.prop.b; // error: property 'b' doesn't exist on type { a: string }
    }
}

If the while enclosure is removed the error doesn't occur (same with for, I only used while for simplicity).

[emilgpa]

@malibuzios thanks!

[emilgpa]

Apparently, only it occurs within iterators..

[malibuzios]

Interestingly, the type inferred within the second guard block for x is B and the type inferred for x.prop is also correct:

    } else if (x instanceof B) {
        x; // has type B
        x.prop; // has type { b: string }
        x.prop.b; // error: property 'b' doesn't exist on type { a: string }
    }