Unexpected type narrowing for variable (outer scope) assignment in function

[cschuller]

TypeScript Version: 3.8.0-dev20200122

Search Terms:
property does not exist on type never

Code

class Person {
    name: string;
    constructor(name: string) {
        this.name = name;
    }
}
 
let foo: Person | null = null;

function initialize() {
    foo = new Person('foo');
}

initialize();

if (foo) {
    console.log(foo.name); // Property 'name' does not exist on type 'never'.
}

Expected behavior:
No compile error.

Actual behavior:
Code throws a Property 'name' does not exist on type 'never'.

Playground Link:
playground example

Related Issues:
#35644
Labelled as fix available for 3.8.1, but does not work for 3.8.0-dev20200122

[jcalz]

duplicate of #9998; the compiler has no idea that initialize() has an implication for the type of foo.

[cschuller]

@jcalz Thanks - Quite a long discussion, good arguments on both sides. I am more in favor of turning the optimistic prediction off (or make it configurable or warning level), but at least we could re-phrase the error message.