Recursive protocols seem to crash pylance (maximum call stack exceeded)

[jaycosaur]

Environment data

Language Server version: v2020.8.0
OS and version: macOS Catalina 10.15.5 (19F101)
Python version: 3.8.2
VSCode version: 1.47.3

Expected behaviour

Should be able to handle recursive protocols and not crash the tool.

Actual behaviour

Crashes out tool with RangeError: Maximum call stack size exceeded and Error performing analysis: RangeError: Maximum call stack size exceeded messages

Code Snippet / Additional information

The below code snippet is a modified version of mypys recursive protocol example which crashes out pylance.

from typing import Optional, Protocol


class TreeLike(Protocol):
    value: int

    @property
    def left(self) -> Optional["TreeLike"]:
        ...

    @property
    def right(self) -> Optional["TreeLike"]:
        ...


class SimpleTree:
    value: int

    @property
    def left(self) -> Optional["SimpleTree"]:
        return self._left

    @property
    def right(self) -> Optional["SimpleTree"]:
        return self._right

    def __init__(self, value: int) -> None:
        self.value = value
        self._left: Optional["SimpleTree"] = None
        self._right: Optional["SimpleTree"] = None


root: TreeLike = SimpleTree(0)

Though rewriting like the following presents no errors and passes successfully.

from typing import Optional, Protocol
from dataclasses import dataclass


class TreeLike(Protocol):
    value: int
    left: Optional["TreeLike"]
    right: Optional["TreeLike"]


@dataclass
class SimpleTree:
    value: int
    left: Optional["SimpleTree"] = None
    right: Optional["SimpleTree"] = None


root: TreeLike = SimpleTree(0)

[erictraut]

Thanks for the bug report and the clear repro steps!

This will be fixed in the next version of Pylance. I've added your sample to our unit tests to prevent future regressions.

[jakebailey]

This issue has been fixed in version 2020.8.1, which we've just released. You can find the changelog here: https://github.com/microsoft/pylance-release/blob/master/CHANGELOG.md#202081-13-august-2020