Generic Constraints working incorrectly

[hronro]

TypeScript Version: 3.2.2

Code

type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>;

interface IName {
  name: string;
}

const callWithName =
  <T extends IName, R>(fn: (origianlArgs: T) => R, name: string) =>
    (arg: Omit<T, 'name'>) =>
      fn({
        ...arg,
        name,
      });

const greeting = (arg: { name: string }) => {
  console.log(`Hello ${arg.name}`);
}

const greetingToTom = callWithName(greeting, 'Tom');

greetingToTom({});

Expected behavior:
shouldn't have any type error

Actual behavior:
has a error:

Argument of type '{ name: string; }' is not assignable to parameter of type 'T'.

Playground Link:

https://www.typescriptlang.org/play/index.html#src=type%20Omit%3CT%2C%20K%20extends%20keyof%20T%3E%20%3D%20Pick%3CT%2C%20Exclude%3Ckeyof%20T%2C%20K%3E%3E%3B%0A%0Ainterface%20IName%20%7B%0A%20%20name%3A%20string%3B%0A%7D%0A%0Aconst%20callWithName%20%3D%0A%20%20%3CT%20extends%20IName%2C%20R%3E(fn%3A%20(origianlArgs%3A%20T)%20%3D%3E%20R%2C%20name%3A%20string)%20%3D%3E%0A%20%20%20%20(arg%3A%20Omit%3CT%2C%20'name'%3E)%20%3D%3E%0A%20%20%20%20%20%20fn(%7B%0A%20%20%20%20%20%20%20%20...arg%2C%0A%20%20%20%20%20%20%20%20name%2C%0A%20%20%20%20%20%20%7D)%3B%0A%0Aconst%20greeting%20%3D%20(arg%3A%20%7B%20name%3A%20string%20%7D)%20%3D%3E%20%7B%0A%20%20console.log(%60Hello%20%24%7Barg.name%7D%60)%3B%0A%7D%0A%0Aconst%20greetingToTom%20%3D%20callWithName(greeting%2C%20'Tom')%3B%0A%0AgreetingToTom(%7B%7D)%3B

Related Issues:

[jack-williams]

EDIT: Outdated comment. I wont delete the comment so you can read the history if you want.

[jack-williams]

No problem. If I were you I would edit your initial post with the new example (and I'll probably remove / edit my comment too).

This looks familiar to other posts I've seen but I can't say if this is a duplicate. Your name parameter should be something like T["name"] though, as it might be the case that T is instantiated with something more precise than string, like "foobar".

This seems to boil down to whether { name: T["name"]; } & Pick<T, Exclude<keyof T, "name">> should be assignable to T.

Sorry I can't be more help!

[hronro]

@jack-williams Thanks. And I found a issue here which is similar: #28748

So maybe my issue is duplicated?

[jack-williams]

Possibly; this issue also looks similar #28821. I don't know enough to say if this is a duplicate so I would wait for someone more knowledgeable to drop by.

[DanielRosenwasser]

Potentially a dupe; I'll let @ahejlsberg decide.

[sveyret]

Also similar to #28884.

[ahejlsberg]

Duplicate of #28884.

[typescript-bot]

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