Type inference seems to ignore reachability analysis

[tapetersen]

Describe the bug
Not important as such in any specific case but wanted to report.

While pyright detects that a section of code is unreachable it still uses these statements for type inference of a variable.

Code or Screenshots
In the following code pyright excludes the possibility of a=5 since it detects the overwrite later but it has also marked that code as unreachable

# pyright: strict

from typing import Any, Literal
from typing_extensions import assert_type, Never


def no_return() -> Never:
    raise Exception()

class CtxMgr:
    def __enter__(self):
        return self

    def __exit__(self, *exc_info: Any) -> bool:
        return True

a = None
with CtxMgr():
    a = 5
    no_return()
    a = 10

assert a is not None
assert_type(a, Literal[5])

playground link

VS Code extension or command-line
Pylance language server 2023.12.1 (pyright a78e2b1)

[erictraut]

Good catch. Yes, there was a subtle (and longstanding) bug in the code flow analysis logic. This will be addressed in the next release.

[erictraut]

This is addressed in pyright 1.1.344, which I just published. It will also be included in a future release of pylance.