Intersection of non-null and null is not deduced to be never #33274

The intersection of non-null/undefined types with null and undefined is not deduced to be never. Instead, things like string & null persist unchanged. (This is with strict null checking.) This also applies to singleton types, so the type "a" & "b" is not deduced to be never.

TypeScript Version: 3.5.1

Search Terms: primitive null intersection never

Code

type T = string & null;
type U = T extends never ? number : never;
const a: U = 1;

Expected behavior: T is deduced to be never, so U is number, so it compiles.

Actual behavior: The code does not compile because T is not deduced to be never and so U is never.

Playground Link: https://www.typescriptlang.org/play/#code/C4TwDgpgBAKlC8UDOwBOBLAdgcygMikwFcAbEgbgChRIoBVBWKCAD2AkwBMlCIA3CKigB+QkQC2AI0FQAXLwGoqAYwD2mFFACG8hogCM5IA