Partial type fails to narrow in spite of check for undefined II

[NoelAbrahams]

TypeScript Version: 3.4.0
Search Terms: Partial switch

Code

const enum BarEnum {
    bar1 = 1,
    bar2 = 2,
}

type TypeBar1 = {

    foo: BarEnum.bar1;
    array: number[];
};

type TypeBar2 = {

    foo: BarEnum.bar2;
    array: number[];
};

type UnionOfBar = TypeBar1 | TypeBar2;

const value: Partial<UnionOfBar> = {} as any;

if (value.array) {

    value.array.toString(); // Okay

    switch (value.foo) {

        case BarEnum.bar1:
            value.array.toString(); // Error: Object is possibly undefined
            break;
    }
}

Expected behavior:
No compiler error

Actual behavior:
The compiler complains of value.array being undefined

Playground Link:
Not able to reproduce on the playground. I think this is a bug in 3.4.

Related Issues:
This is another version of the bug reported here: #29496

[j-oliveras]

It can be reproduced on playground enabling strictNullChecks under Options.

Probably related to #9998.

[jack-williams]

Narrowing by discriminant (which is happening at value.foo in the switch) narrows from the declared type of value, thus ignoring the previous property narrowing obtained from value.array. This is probably a design limitation / working as intended.

[NoelAbrahams]

It may be a design limitation, but it certainly cannot be working as intended - unless the intention is to surprise the user!

[madhavmalhotra-3089]

I am facing the same issue.

[sigorilla]

+1, example

[threehams]

The examples in this issue are fixed in 3.8. I don't know what change fixed them, though.

[NoelAbrahams]

@threehams, you're right: it's been fixed. Thanks.