Intersection of mapped type of with omit not compatible

[robinchrist]

Bug Report

🔎 Search Terms

omit, mapped type, intersection

🕗 Version & Regression Information

• This is the behavior in every version I tried, 3.5.1 up to 4.9.4

⏯ Playground Link

Playground link with relevant code

💻 Code

type Column = {value: number}


type RemoveTitles<Type> = {
  [Property in keyof Type]: Omit<Type[Property], 'title'>;
};

class TableDataGenerator2<
  TIn extends { [colName: string]: Column & { title: string } },
  TAdd extends { [colName: string]: Column & { title: string } } = {}
> {

  constructor(
    private callback: (
      index: number,
      row: RemoveTitles<TIn>
    ) => Promise<RemoveTitles<TAdd>>
  ) {}

  chain<TAdd2 extends { [colName: string]: Column & { title: string } }>(
    cb: (
      index: number,
      row: RemoveTitles<TIn> & RemoveTitles<TAdd>
    ) => Promise<RemoveTitles<TAdd2>>
  ): TableDataGenerator2<TIn, TAdd & TAdd2> {
    return new TableDataGenerator2<TIn, TAdd & TAdd2>(async (index, input) => {
      const elem = await this.callback(index, input);
      const elem2 = await cb(index, { ...elem, ...input });
      return { ...elem2, ...elem };
    });
  }
}

Argument of type '(index: number, input: RemoveTitles<TIn>) => Promise<RemoveTitles<TAdd2> & RemoveTitles<TAdd>>' is not assignable to parameter of type '(index: number, row: RemoveTitles<TIn>) => Promise<RemoveTitles<TAdd & TAdd2>>'.
  Type 'Promise<RemoveTitles<TAdd2> & RemoveTitles<TAdd>>' is not assignable to type 'Promise<RemoveTitles<TAdd & TAdd2>>'.
    Type 'RemoveTitles<TAdd2> & RemoveTitles<TAdd>' is not assignable to type 'RemoveTitles<TAdd & TAdd2>'.

🙁 Actual behavior

TypeScript does not detect that RemoveTitles<T1> & RemoveTitles<T2> is compatible with RemoveTitles<T1 & T2>

🙂 Expected behavior

RemoveTitles<T1> & RemoveTitles<T2> is compatible with RemoveTitles<T1 & T2> and should be treated as equivalent, as can be seen in this example

[RyanCavanaugh]

TypeScript does not detect that RemoveTitles<T1> & RemoveTitles<T2> is compatible with RemoveTitles<T1 & T2>

It's not really clear how it could, either - the definition of this type is sufficiently complex that there isn't an obvious way to identify this fact apart from some very difficult counterfactual reasoning about possible inhabitants of T1 and T2.