Discriminant narrow not work when not union type.

[ShuiRuTian]

TypeScript Version: 3.7.x-dev.201xxxxx

Search Terms:

Code

// A *self-contained* demonstration of the problem follows...
// Test this by running `tsc` on the command-line, rather than through another build tool such as Gulp, Webpack, etc.
interface X {
    type: 'A'
}

function ffff3(x: X) {
    if (x.type === 'A') {
        return;
    }
    x  // should be never, but still X.
}

Expected behavior:
the type of variable x in the last line of the function should be narrowed to never.

Actual behavior:
It is not narrowed.

Playground Link:
https://www.typescriptlang.org/play/index.html#code/JYOwLgpgTgZghgYwgAgBrIN4Chm+WATwAcIAuZAcgEEKsBfLUSWRFATUxz0JPIrdoMsMAK4gEYYAHsQyGPJgBmABQAPcqgA+bAJSc8yYDGRqAdDxQBea5Rp7sBg1AhgRUEAG4uuBgaMnVc2IrG34Ke29HZ1d3LwNfPFV6IA

Related Issues:

[RyanCavanaugh]

Duplicate e.g. #38963