mirror of https://github.com/astral-sh/ruff
674d3902c6
## Summary
The following snippet currently errors because we widen the inferred
type, even though `X` is covariant over `T`. If `T` was contravariant or
invariant, this would be fine, as it would lead to an assignability
error anyways.
```python
class X[T]:
def __init__(self: X[None]): ...
def pop(self) -> T:
raise NotImplementedError
# error: Argument to bound method `__init__` is incorrect: Expected `X[None]`, found `X[int | None]`
x: X[int | None] = X()
```
There are some cases where it is still helpful to prefer covariant
declared types, but this error seems hard to fix otherwise, and makes
our heuristics more consistent overall.
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| .. | ||
| corpus | ||
| mdtest | ||
| primer | ||
| README.md | ||
README.md
Markdown files within the mdtest/ subdirectory are tests of type inference and type checking;
executed by the tests/mdtest.rs integration test.
See crates/ty_test/README.md for documentation of this test format.