Overloads should be merged to consider whether a union-typed argument is valid

[pelotom]

TypeScript Version: 2.7.0-dev.201xxxxx

Code

interface Foo {
  x: number
}

interface Bar {
  y: boolean
}

interface Baz {
  (foo: Foo): void
  (bar: Bar): void
}

declare const baz: Baz
declare const foobar: Foo | Bar

baz(foobar)

Expected behavior:

Should compile.

Actual behavior:

The last line has a type error,

Argument of type 'Foo | Bar' is not assignable to parameter of type 'Bar'.
  Type 'Foo' is not assignable to type 'Bar'.
    Property 'y' is missing in type 'Foo'.

[mhegazy]

Duplicate of #14107

[pelotom]

Thanks for the pointer, closing.