[ty] Avoid falling back to `Unknown` when collecting type context constraints (#28297)
During fixpoint iteration, we use argument types inferred from previous
iterations as type context for subsequent iterations. Arguments being
forwarded to a `ParamSpec` are initially inferred without type context,
as the type of the callable has not yet been inferred, and so we clear
their types after the initial iteration. However, we currently fallback
to `Unknown` as type context for arguments that have not yet been
inferred, even if they have been intentionally cleared, which can
pollute the types inferred in the next iteration. We should instead
avoid providing any type context in this case.
```py
from typing import TypedDict, Callable
class Payload(TypedDict):
x: int
def forward[**P](function: Callable[P, None], /, *args: P.args, **kwargs: P.kwargs) -> None:
function(*args, **kwargs)
def pair[T](first: T, second: T) -> None: ...
def _(payload: Payload):
forward(pair, reveal_type({"x": 1}), payload) # main: dict[str, int], fixed: Payload
```
ruff
6077dc3d - [ty] Avoid falling back to `Unknown` when collecting type context constraints (#28297)
