Seemingly invalid error on object that correctly provides a partial generic interface.

[Anupheaus]

TypeScript Version: 3.1.1-insiders.20180925

Search Terms:
is not assignable to, partial

Code

interface IItem {
  id: string;
  isOpen: boolean;
}

interface IRecord {
  id: string;
}

type Upsertable<T> = Partial<T> & { id: string; };

class A<T extends IItem = IItem> {
  protected setItem(partialItem: Upsertable<T>): void {

  }
}

interface IMyItem extends IItem {
  title: string;
}

class B<T extends IMyItem> extends A<T> {
  constructor() {
    super();
    const id: string = 'uniqueId';
    const isOpen: boolean = false;
    this.setItem({ id, isOpen }); // error here: 
    // Argument of type '{ id: string; isOpen: boolean; }' is not assignable to parameter of type 'Upsertable<T>'.
    // Type '{ id: string; isOpen: boolean; }' is not assignable to type 'Partial<T>'.
  }
}

Expected behavior:
The given properties are valid with the type IMyItem, which in turn extends from IItem, and as all properties bar id are optional, having only isOpen and id should be fine.

Actual behavior:
Errors with Argument of type '{ id: string; isOpen: boolean; }' is not assignable to parameter of type 'Upsertable<T>'. Type '{ id: string; isOpen: boolean; }' is not assignable to type 'Partial<T>'.

Playground Link:
http://www.typescriptlang.org/play/#src=interface%20IItem%20%7B%0D%0A%20%20id%3A%20string%3B%0D%0A%20%20isOpen%3A%20boolean%3B%0D%0A%7D%0D%0A%0D%0Ainterface%20IRecord%20%7B%0D%0A%20%20id%3A%20string%3B%0D%0A%7D%0D%0A%0D%0Atype%20Upsertable%3CT%3E%20%3D%20Partial%3CT%3E%20%26%20%7B%20id%3A%20string%3B%20%7D%3B%0D%0A%0D%0Aclass%20A%3CT%20extends%20IItem%20%3D%20IItem%3E%20%7B%0D%0A%20%20protected%20setItem(partialItem%3A%20Upsertable%3CT%3E)%3A%20void%20%7B%0D%0A%0D%0A%20%20%7D%0D%0A%7D%0D%0A%0D%0Ainterface%20IMyItem%20extends%20IItem%20%7B%0D%0A%20%20title%3A%20string%3B%0D%0A%7D%0D%0A%0D%0Aclass%20B%3CT%20extends%20IMyItem%3E%20extends%20A%3CT%3E%20%7B%0D%0A%20%20constructor()%20%7B%0D%0A%20%20%20%20super()%3B%0D%0A%20%20%20%20const%20id%3A%20string%20%3D%20'uniqueId'%3B%0D%0A%20%20%20%20const%20isOpen%3A%20boolean%20%3D%20false%3B%0D%0A%20%20%20%20this.setItem(%7B%20id%2C%20isOpen%20%7D)%3B%0D%0A%20%20%7D%0D%0A%7D

Related Issues:
Maybe this bug: #12731?

[RyanCavanaugh]

See #13442 or its linked issues

[typescript-bot]

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