`@interface` tag on discriminated union results in inappropriate broadening of some property types, omission of others

[Oblarg]

Consider:

type Foo = {
  key: 'foo'
  bar: 'bar1'
}

type Bar = {
  key: 'bar'
  bar: 'bar2'
  baz: any
}

/**
 * @interface
 */
type DiscriminatedUnion = Foo | Bar;

This renders as:

{
  key: 'foo' | 'bar'
  bar: 'bar1 | 'bar2'
}

The type above is overly-broad with respect to the key and bar properties (their values are correlated), and omits the baz property entirely.

[Gerrit0]

The way @interface works is effectively to run your type through { [K in keyof T]: T[K] } and convert that, TS interfaces don't support unions like this, and neither does @interface

[Oblarg]

I am aware that TS interface does not support discriminated union semantics - but I think it's a bad behavior to just strip them/represent them wrongly without warning. It'd be better to error here.