Bug Report

I am seeing an error when trying to initialise a variable with

const result: Partial<T> & { bar: boolean } = { bar: false };

where T is a type parameter in a generic function. The error is as follows:

4:9 - error TS2322: Type '{ bar: false; }' is not assignable to type 'Partial<T> & { bar: boolean; }'.
  Type '{ bar: false; }' is not assignable to type 'Partial<T>'.

4   const result: Partial<T> & { bar: boolean } = { bar: false };
          ~~~~~~

If T is a type that is not a generic parameter then there are no issues, and also adding an additional step as follows leads to no errors:

  const part: Partial<T> = {};
  const result: Partial<T> & { bar: boolean } = { ...part, bar: false };

I have included a full code snippet below.

🔎 Search Terms

• "is not assignable partial"
• "intersection type generic function error"

🕗 Version & Regression Information

• This is the behaviour in every version I tried, and I reviewed the FAQ for entries about 'Common "Bugs" That Aren't Bugs'.

⏯ Playground Link

Playground link with relevant code

💻 Code

type PartialWithBar<T> = Partial<T> & { bar: boolean };

export const erroringFunc = <T extends Record<string, unknown>>(): PartialWithBar<T> => {
  const result: PartialWithBar<T> = { bar: false };
  return result;
};

export const workingFunc = <T extends Record<string, unknown>>(): PartialWithBar<T> => {
  const part: Partial<T> = {};
  const result: PartialWithBar<T> = { ...part, bar: false };
  return result;
};

type MyType = { a: number };

export const workingFunc2 = (): PartialWithBar<MyType> => {
  const result: PartialWithBar<MyType> = { bar: false };
  return result;
};

🙁 Actual behavior

erroringFunc causes an error, while workingFunc does not.

🙂 Expected behavior

Either errorringFunc should not cause any errors, or workingFunc should cause an error - the two should be consistent.