The type of async_transactional is incorrect

[jekozyra]

The return of the decorated function evaluates correctly at runtime but the typechecker thinks that it is Coroutine[Unknown, Unknown, Unknown], which is incorrect.

Environment details

• OS type and version: OSX 15.4.1
• Python version: 3.13
• pip version: 24.2
• google-cloud-firestore version: 2.20.2

pyright 1.1.396 is used as the typechecker.

Steps to reproduce

1. Use the async_transactional decorator as detailed in the docs
2. The return of the decorated function evaluates correctly at runtime but the typechecker thinks that it is Coroutine[Unknown, Unknown, Unknown]

Code example

import asyncio

import firebase_admin
from firebase_admin import firestore_async
from google.cloud.firestore_v1 import AsyncClient as AsyncFirestoreClient
from google.cloud.firestore_v1.async_transaction import (
    AsyncTransaction,
    async_transactional,
)


async def func(db: AsyncFirestoreClient) -> None:
    transaction = db.transaction()
    city_ref = db.collection("cities").document("SF")

    @async_transactional
    async def update_in_transaction(transaction: AsyncTransaction) -> str:
        snapshot = await city_ref.get(transaction=transaction)
        transaction.update(city_ref, {"population": snapshot.get("population") + 1})
        return "done"

    res = await update_in_transaction(transaction)
    print(type(res))  # evaluates to <class 'str'> at run time but Coroutine[Unknown, Unknown, Unknown] in the typechecker

async def func2(db: AsyncFirestoreClient) -> str:
    transaction = db.transaction()
    city_ref = db.collection("cities").document("SF")

    @async_transactional
    async def update_in_transaction(transaction: AsyncTransaction) -> str:
        snapshot = await city_ref.get(transaction=transaction)
        transaction.update(city_ref, {"population": snapshot.get("population") + 1})
        return "done"

    return await update_in_transaction(transaction)  # typechecker errors


if __name__ == "__main__":
    app = firebase_admin.initialize_app(
        options={"projectId": "poggio-local-experiments"}
    )
    db = firestore_async.client(app)
    asyncio.run(func(db=db))
    asyncio.run(func2(db=db))