mirror of https://github.com/astral-sh/ruff
33b942c7ad
This manifested as an error when inferring the type of a PEP-695 generic
class via its constructor parameters:
```py
class D[T, U]:
@overload
def __init__(self: "D[str, U]", u: U) -> None: ...
@overload
def __init__(self, t: T, u: U) -> None: ...
def __init__(self, *args) -> None: ...
# revealed: D[Unknown, str]
# SHOULD BE: D[str, str]
reveal_type(D("string"))
```
This manifested because `D` is inferred to be bivariant in both `T` and
`U`. We weren't seeing this in the equivalent example for legacy
typevars, since those default to invariant. (This issue also showed up
for _covariant_ typevars, so this issue was not limited to bivariance.)
The underlying cause was because of a heuristic that we have in our
current constraint solver, which attempts to handle situations like
this:
```py
def f[T](t: T | None): ...
f(None)
```
Here, the `None` argument matches the non-typevar union element, so this
argument should not add any constraints on what `T` can specialize to.
Our previous heuristic would check for this by seeing if the argument
type is a subtype of the parameter annotation as a whole — even if it
isn't a union! That would cause us to erroneously ignore the `self`
parameter in our constructor call, since bivariant classes are
equivalent to each other, regardless of their specializations.
The quick fix is to move this heuristic "down a level", so that we only
apply it when the parameter annotation is a union. This heuristic should
go away completely 🤞 with the new constraint solver.
|
||
|---|---|---|
| .. | ||
| module_resolver | ||
| semantic_index | ||
| types | ||
| ast_node_ref.rs | ||
| db.rs | ||
| diagnostic.rs | ||
| dunder_all.rs | ||
| lib.rs | ||
| lint.rs | ||
| list.rs | ||
| module_name.rs | ||
| node_key.rs | ||
| place.rs | ||
| program.rs | ||
| pull_types.rs | ||
| python_platform.rs | ||
| rank.rs | ||
| semantic_index.rs | ||
| semantic_model.rs | ||
| site_packages.rs | ||
| subscript.rs | ||
| suppression.rs | ||
| types.rs | ||
| unpack.rs | ||