Unions and intersections of type predicates produce wrong type

TypeScript Version: 2.5.0-dev.20170803

Code

type Foo = typeof ts.isDoStatement | typeof ts.isWhileStatement;

Expected behavior: Resulting type should be (node: ts.Node) => node is (ts.DoStatement | ts.WhileStatement)

Actual behavior: Resulting type is (node: ts.Node) => node is ts.DoStatement

It seems to just take the first one.

[SamPruden]

type predicate

I knew using “type guards” like that wasn’t quite right. 😂

[aluanhaddad]

It appears to just grab the first type predicate and ignore the rest.

Here is a self-contained repro (2.5.0-dev.20170808)

type IsStringOrNumber = ((x: any) => x is number) | ((x: any) => x is string);

declare const x: any;

if ((((x: any) => true) as IsStringOrNumber)(x)) {
    x.toFixed();
}

Intersecting type predicates seems to have the same result, only the first signature is considered.

type IsStringAndNumber = ((x: any) => x is number) & ((x: any) => x is string);