Omitting a property on a discriminated union type #54525
Description
Bug Report
When using Omit on a discriminated union type, the properties unique to each "branch" of the union type are lost.
🔎 Search Terms
Omit, union, discriminated union
🕗 Version & Regression Information
Tested on TypeScript 4.8.4 and on the nightly version (June 5th, 2023)
⏯ Playground Link
Alternative demo (a different way to do discriminated unions, which is also affected)
💻 Code
type T = {
name: string,
type: 1,
prop1: string,
} | {
name: string,
type: 2,
prop2: string,
}
type T2 = Omit<T, 'name'>
🙁 Actual behavior
T2 is interpreted as such by TypeScript:
type T2 = {
type: 1 | 2;
}
And the following object is seen as invalid:
const obj: T2 = {
type: 2,
prop2: 'abcd', // "prop2 does not exist on type T2"
}
🙂 Expected behavior
T2 should be interpreted like this instead:
type T2 = {
type: 1;
prop1: string;
} | {
type: 2;
prop2: string;
}
And the object described above should be seen as valid.