{ tag: 'foo' | 'bar' } should be assignable to { tag: 'foo' } | { tag: 'bar' }

[pelotom]

Logically it seems like this should work:

declare const x: { tag: 'foo' | 'bar' };

const foobar: { tag: 'foo' } | { tag: 'bar' } = x
//    ^^^^^^ Type '{ tag: "foo" | "bar"; }' is not assignable to type '{ tag: "foo"; } | { tag: "bar"; }'.
//             Type '{ tag: "foo" | "bar"; }' is not assignable to type '{ tag: "bar"; }'.
//               Types of property 'tag' are incompatible.
//                 Type '"foo" | "bar"' is not assignable to type '"bar"'.
//                   Type '"foo"' is not assignable to type '"bar"'.

Of course this is only the case if there aren't additional fields with differing types for tag to discriminate, so this is admittedly perhaps a niche use case.

[mhegazy]

Duplicate of #14865