1.1.373 issue - Expected class but received "Literal[0]" & Too few type arguments provided for "FixtureFunction"

[lexicalunit]

Describe the bug
In version 1.1.373 I'm getting a bunch of cryptic errors with code that passed fine in version 1.1.372.

Code or Screenshots

I was able to create a minimal example:

from sqlalchemy.engine import create_engine
from sqlalchemy.orm import sessionmaker

database_url = "whatever:///does/not/matter"
engine = create_engine(database_url)
connection = engine.connect()
session_maker = sessionmaker(bind=connection)
session = session_maker()
rows = session.execute("SELECT xid FROM guilds").fetchall()
xids = [int(row[0]) for row in rows]

You can see the full error logs in my github actions workflow: https://github.com/lexicalunit/spellbot/actions/runs/10168666850/job/28123798890

VS Code extension or command-line

• Command Line

➜ poetry run pyright tests src example.py
/path/to/spellbot/example.py
  /path/to/spellbot/example.py:10:17 - error: Expected class but received "Literal[0]" (reportGeneralTypeIssues)
  /path/to/spellbot/example.py:10:17 - error: Too few type arguments provided for "FixtureFunction[SimpleFixtureFunction@FixtureFunction, FactoryFixtureFunction@FixtureFunction]"; expected 2 but received 1 (reportInvalidTypeForm)

However, if I run pyright on a single file, I get no error:

➜ poetry run pyright example.py
0 errors, 0 warnings, 0 informations

It only happens when I execute pyright on all my files.

Additional Information

➜ poetry run pip freeze | grep -iE "sqlalchemy|pyright"
pyright==1.1.373
SQLAlchemy==2.0.31
sqlalchemy-stubs==0.4
SQLAlchemy-Utils==0.41.2

➜ poetry run python --version
Python 3.12.4

[erictraut]

I'm not able to repro what you're seeing. If I install the "sqlalchemy-stubs` package, I see no errors from pyright. I'm guessing that you have something else installed in your venv that's affecting the results. Are you able to repro the problem with a clean venv?

My understanding is that sqlalchemy 2.x is fully typed — that is, it has inline type information — and that it doesn't require the use of an external stub library. By adding the stub library, you're overriding the type information provided by the library maintainers with outdated and incomplete type information. I think the stub library is intended for use with sqlalchemy 1.x, which didn't have type information. You might want to try removing it from your environment. If I don't install sqlalchemy-stubs, I receive a type error for the session.execute call because this call apparently doesn't accept a str argument.

[lexicalunit]

I get the same errors listed above if I uninstall sqlalchemy-stubs. However removing these stubs causes additional errors like, for example:

test_games.py:338:24 - error: Argument of type "Column[int]" cannot be assigned to parameter "author_xid" of type "int"
    "Column[int]" is incompatible with "int" (reportArgumentType)

[lexicalunit]

Weirdly, I don't get the same type errors in the editor with pylance that I do from pyright. Not sure what that's about either.

[erictraut]

Pylance is typically using a version of pyright that's one to four weeks behind. You could try switching to the prerelease version of pylance.

[erictraut]

Moving to a discussion topic because I don't think this is a bug in pyright.

[lexicalunit]

Reverting to 1.1.372 seems to fix the issue for now at least.

[kjagiello]

Googling for Too few type arguments provided for "FixtureFunction[SimpleFixtureFunction@FixtureFunction, FactoryFixtureFunction@FixtureFunction]"... lead me to this discussion.

I have bumped pyright in a project and got a multitude of these as well. The issue seems to stem from the pytest-asyncio package. For some reason, as soon as pytest_asyncio.fixture appears in the code, all the untyped arguments become FixtureFunction[SimpleFixtureFunction@FixtureFunction, FactoryFixtureFunction@FixtureFunction].

I think this can serve as a minimal repro case:

import pytest_asyncio

pytest_asyncio.fixture

def f(x):
    x["y"]

Output:

repro.py:6:7 - error: Too few type arguments provided for "FixtureFunction[SimpleFixtureFunction@FixtureFunction, FactoryFixtureFunction@FixtureFunction]"; expected 2 but received 1 (reportInvalidTypeForm)
repro.py:6:8 - error: "y" is not defined (reportUndefinedVariable)

Packages:

pyright==1.1.374
pytest==8.3.2
pytest-asyncio==0.23.8

It seems like this issue appeared in 1.1.373.

[kjagiello]

An attempt to create a repro case without any external dependencies:

from collections.abc import Callable
from typing import TypeAlias, TypeVar

A = TypeVar("A")
B = TypeVar("B")
C: TypeAlias = A | B
D: TypeAlias = Callable[[], C]

def f(x):
    x["y"]

(playground)

The union alias seems to be important. For example this does not exhibit the same issue:

from collections.abc import Callable
from typing import TypeAlias, TypeVar

A = TypeVar("A")
B = TypeVar("B")
C: TypeAlias = Callable[[], A | B]

def f(x):
    x["y"]

[erictraut]

Thanks for the great repro steps! This turns out to be a very bad bug in pyright. It has existed for a long time — at least a couple of years. It results in internal data structure corruption which results in very strange behaviors. I'm really surprised this hasn't been seen (or reported) previously. The "mypy_primer" regression test that we run on every pyright PR indicates that this bug was affecting other code bases.

Thanks again for reporting the issue and taking the time to isolate it. Much appreciated!

This will be addressed in the next release.