unexpected behaviour when use Omit with Insection Types

TypeScript Version: 3.9.2

Search Terms:
omit, insection types

Code

interface User {
  type: 'user';
  name: string;
  age: number;
  occupation: string;
}

interface Admin {
  type: 'admin';
  name: string;
  age: number;
  role: string;
}

type PowerUser = Omit<User & Admin, 'type'> & {
  type: 'powerUser'
};
let p: PowerUser = {
  type: 'powerUser',
  name: 'hello',
  age: 123,
  occupation: '123',
  role: '123'
}
console.log(p)

Expected behavior:
no error

Actual behavior:

test.ts:21:3 - error TS2322: Type 'string' is not assignable to type 'never'.

21   name: 'hello',
     ~~~~

test.ts:22:3 - error TS2322: Type 'number' is not assignable to type 'never'.

22   age: 123,
     ~~~

test.ts:23:3 - error TS2322: Type 'string' is not assignable to type 'never'.

23   occupation: '123',
     ~~~~~~~~~~

test.ts:24:3 - error TS2322: Type 'string' is not assignable to type 'never'.

24   role: '123'
     ~~~~

Playground Link:
https://www.typescriptlang.org/play/?ssl=1&ssc=1&pln=26&pc=15#code/LAKAlgdgLgpgTgMwIYGMYAICqBne6Deo66UAngA4wBc6A5AK65y0DcR6ESAttetlHEgBzNiGJIhvCPS4AjeKOIB7FCnrkkUMEog1+giCNABfUKEixEqDAEEAJl0gF2ZSjVpIHkVu0489AsKK6BJSMvJwwXBKADa8+kEmZiCuGAAKSgDu8Dh4ALzoAPKOUAA8uXDoAGTo9o4QADR0qbQAfNXOYiQUvLTkWTlMtCaicVDo5DQZ2XAV6AWEXanu-TMVtA2+3L0AFjAxMUob7KE0AIwATADMm10qahpaOu6XV8dd0XEv18MgpiAoHTYWIwAB0hyEAApyABKIA
Related Issues:

This is related to a recent change in behavior from #36696, where intersection resulting in a field of type never are reduced to never.

You can change your types to this:

type PowerUser = Omit<User,'type'> & Omit<Admin,'type'>  & {
  type: 'powerUser'
};

Playground Link

Titian Cernicova-Dragomir (@dragomirtitian)

Titian Cernicova-Dragomir (@dragomirtitian) has it right 👆

This issue has been marked 'Working as Intended' and has seen no recent activity. It has been automatically closed for house-keeping purposes.

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unexpected behaviour when use Omit with Insection Types #39359

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unexpected behaviour when use Omit with Insection Types #39359

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dragomirtitian commented on Jul 1, 2020

RyanCavanaugh commented on Jul 7, 2020

typescript-bot commented on Jul 10, 2020

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