firestore QueryDocumentSnapshot type mismatch between compat & new lib

[goleary]

[REQUIRED] Describe your environment

• Operating System version: window 11
• Browser version: n/a
• Firebase SDK version: 9.6.9
• Firebase Product: firestore

[REQUIRED] Describe the problem

There is a type mismatch between the QueryDocumentSnapshot exported by firebase/firestore & firebase/compat/app.

We've are hoping to incrementally adopt the modular style/syntax of version 9 of this library.

We have converters that are defined using the types exported from firebase/firestore, but we use these converters with code exported from firebase/compat/app/firebase/compat/firestore.

i.e.

import firebase from 'firebase/compat/app';
import 'firebase/compat/firestore';

import ThingyConverter from './converter'; // defined using type from new module

...
const docRef = firebase.firestore().doc('col/1).withConverter(ThingConverter)

Attempting to do so result in a type error.

Type 'firebase.default.firestore.QueryDocumentSnapshot<firebase.default.firestore.DocumentData>' is not assignable to type 'import(".../firebase-converter-type-repro/node_modules/@firebase/firestore/dist/index").QueryDocumentSnapshot<import(".../firebase-converter-type-repro/node_modules/@firebase/firestore/dist/index").DocumentData>'.
  Types of property 'exists' are incompatible.
    Type 'boolean' is not assignable to type '() => this is QueryDocumentSnapshot<DocumentData>'.ts(2322)

I don't understand why these types don't match, they are exported from the same package.

Relevant Code:

This is a minimal repro that exhibits the type error
https://github.com/goleary/firebase-converter-type-repro

[google-oss-bot]

I couldn't figure out how to label this issue, so I've labeled it for a human to triage. Hang tight.

[schmidt-sebastian]

The types exposed by firestore-compat and firestore are not interchangeable. QueryDocumentSnapshot.exists() is a a function in v9, as we would to use the return type as a type-guard. While you should be able to use the QueryDocumentSnapshot from firestore-compat and firestore in all of our Firestore APIs, you cannot assign them to the same variable as TS will correctly detect the signature mismatch.

Let us know if you need more information.

[jbalidiong]

I'll be closing this for now. If the issue persists, feel free to comment and reopen this issue.