[i098]

Summary

Converting a class with an overloaded __new__ to a callable kept every overload, even when the cls annotation of an overload cannot accept the class being converted. For the class in the issue, C[str] was treated as the constructor of C[int] as well.

bind_dunder_new (used by constructor_to_callable) now drops the overloads whose first parameter does not accept the class object. Type parameters are treated as Any on both sides, so these cases keep all their overloads: no cls annotation, cls: type[S] with the overload's own type variable, and a bare generic class such as C. If no overload would remain, the original overload is kept.

Repro, with preset = "default" in pyproject.toml:

from collections.abc import Callable
from functools import partial
from typing import Any, overload

class C[T]:
    @overload
    def __new__(cls: type[C[int]], x: object) -> C[int]: ...
    @overload
    def __new__(cls: type[C[str]], x: str) -> C[str]: ...
    def __new__(cls: type[Any], x: object) -> C[int] | C[str]:
        raise NotImplementedError

wrong: Callable[[str], C[int]] = C[str]
reveal_type(partial(C[str], "x")())

Before: no error on wrong, and revealed type: C[int].

After:

ERROR `type[C[str]]` is not assignable to `(str) -> C[int]` [bad-assignment]
  --> c.py:15:34
 INFO revealed type: C[str] [reveal-type]
  --> c.py:16:12

Fixes #5053

• I am a human, and I fully understand the code I am submitting.

Test Plan

• The first commit adds test_overloaded_new_cls_annotation_as_callable, which fails without the fix (the wrong assignment is accepted and partial(...)() is C[int]). The second commit fixes it.
• test_overloaded_new_cls_annotation_as_callable_variants covers the cases that must keep working: no cls annotation, a bare generic class, type[C[Any]], a type-variable cls, an __init__-only class, and a subclass that inherits the overloaded __new__.
• cargo test -p pyrefly --lib: 9069 passed, 0 failed.
• python3 test.py: passes in full (exit 0), including scrut (204 of 204), tensor shapes, conformance with no generated-file changes, jsonschema and the extension helper tests.

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[meta-codesync]

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