Better display representation for intersection types

[louy]

I'm not sure if this has been discussed before, but join types are mostly unreadable. I think the type should be prettified somehow before being displayed to the user.

TypeScript Version:

1.8

Code

type T1 = {};
type T2 = {test: number};
type J = T1 & T2;

Expected behavior:

var x: J;
typeof x; // {test: number}

Actual behavior:

var x: J;
typeof x; // {} & {test: number}

[JabX]

👍
I use intersections a lot and I would love to have this feature.

[mhegazy]

so just to be clear is the request 1. to remove the empty object type if exists, or 2. to collapse all types. i.e.:

type T = { } & { a: number } & { b: string };

var x: T; // What is x? 
            // 1. { a: number } & { b: string }
            // 2. { a: number, b: string }

[louy]

The second actually.

[mhegazy]

ok one more clarification, i assume this only applies to anonymous types. so 2.a would be the desired behavior.

class C { c: boolean; }

type T = C & { a: number } & { b: string };

var x: T; // What is x? 
            // 2.a C & { a: number; b: string }
            // 2.b { a: number, b: string; c: boolean }

[JabX]

I suppose it's better to limit this to anonymous types, or else it could rapidly go out of control with "big" named types, and you'll lose some type information.

[zpdDG4gta8XKpMCd]

related #6070

[RyanCavanaugh]

Accepting PRs, with a big caveat. This is actually quite a bit trickier than it appears because of how the compiler handles anonymous self-referential types. A PR here should be accompanied by a large test suite of recursively self-referential types to ensure there aren't any lingering runaway recursion bugs.

See also comments in #8228.