pyright sees return type of CSTTransformer.get_metadata() as CodeRange | type[_UNDEFINED_DEFAULT]

[jakkdl]

I started encountering this when updating https://github.com/python-trio/flake8-trio - but it's been 9 months since last time I ran the type tests so it'd be a pain to figure out when exactly it started happening. If needed I can try to binary search for it though, and/or figure out if it's an update in pyright or libcst that messed it up.

repro

foo.py:

import libcst
from libcst.metadata import PositionProvider

class Foo(libcst.CSTTransformer):
    METADATA_DEPENDENCIES = (PositionProvider,)
    def visit_Comment(self, node: libcst.Comment) -> bool:
        metadata = self.get_metadata(PositionProvider, node)
        reveal_type(metadata)
        return False

Works in mypy

$ mypy foo.py
foo.py:8: note: Revealed type is "libcst._position.CodeRange"
Success: no issues found in 1 source file

but pyright gives an additional weird union

$ pyright foo.py 
/tmp/pyright+libcst/foo.py
  /tmp/pyright+libcst/foo.py:8:21 - information: Type of "metadata" is "CodeRange | type[_UNDEFINED_DEFAULT]"
0 errors, 0 warnings, 1 information

versions

• pyright 1.1.350
• mypy 1.8.0
• libcst 1.1.0
• python 3.11.6
• linux

real-life code

https://github.com/python-trio/flake8-trio/blob/dde4479842315a6a64f2f56d3875931ead9f0af3/flake8_trio/visitors/visitor_utility.py#L183