`Error.stack` type definition in lib.es5.d.ts is incorrect / `exactOptionalPropertyTypes` incompatible

Bug Report

🔎 Search Terms

Error.stack, exactOptionalPropertyTypes, ErrnoException

🕗 Version & Regression Information

• This is a type issue
• This changed in #8705 but it took until the 4.4 release for it to surface, thanks to exactOptionalPropertyTypes and it making Error incompatible with a corrected Error-subclass in @types/node: https://github.com/DefinitelyTyped/DefinitelyTyped/pull/55425
• This is the behavior in every version I tried, and I reviewed the FAQ for entries about es5

⏯ Playground Link

Playground link with relevant code which is valid according to the ECMAScript spec and basically every other JS spec out there as .stack isn’t standardized (as far as eg. MDN knows at least)

Edit: @ljharb has an ECMAScript Stage 1 proposal for an Error Stacks spec.

💻 Code

interface MyCoolStack {
    line: string
}

interface MyError extends Error {
    stack: MyCoolStack
}

🙁 Actual behavior

Got error:

Interface 'MyError' incorrectly extends interface 'Error'.
  Types of property 'stack' are incompatible.
    Type 'MyCoolStack | undefined' is not assignable to type 'string'.
      Type 'undefined' is not assignable to type 'string'.

🙂 Expected behavior

One of two:

1. Either that it passes completely…
2. …or at least that it complains the same as it does with exactOptionalPropertyTypes turned off:

Interface 'MyError' incorrectly extends interface 'Error'.
  Types of property 'stack' are incompatible.
    Type 'MyCoolStack | undefined' is not assignable to type 'string | undefined'.
      Type 'MyCoolStack' is not assignable to type 'string'.

Edit: The ECMAScript Stage 1 proposal for an Error Stacks spec defines that the stack should be of type string|undefined, which makes the current type of stack?:string wrong and should be replaced with stack?:string|undefined if one agrees with that specs view of the current state of Error stacks.

[MichaelMitchell-at]

Bumping this, as it’s a major blocker to enabling exactOptionalPropertyTypes in our code base

[ljharb]

That’s for the accessor, if you .call it on a non-error object, for back compat. Fair point tho, that the standard accessor can return undefined.