[udsy19]

Fixes #18644

When functools.partial() receives a **mapping argument, the plugin turned every positional parameter the mapping could fill into a keyword-only one. A plain dict may not contain those keys, so passing them positionally afterwards is fine at runtime, and mypy already accepts the equivalent direct call:

from functools import partial
from typing import Any

def f(a: int, b: str, c: bytes = b"") -> None: ...

d: dict[str, Any] = {}
f(1, "x", **d)      # OK
p = partial(f, **d)
p(1, "x")           # before: error: Too many positional arguments for "f"  [call-arg]

Now a positional parameter that is matched only by non-TypedDict ** arguments stays positional (and optional) in the partial's signature. Parameters given by explicit keyword (partial(f, b="x")) and parameters filled from a TypedDict ** (whose keys mypy treats as present, as in direct calls) remain keyword-only, unchanged.

The Argument 1 has incompatible type "**dict[str, int]" error from the issue's first example is unchanged: the direct call reports the same thing.

Test: testFunctoolsPartialDictUnpackKeepsPositional in check-functools.test covers positional/partial/keyword calls after partial(fn, **d), a function with / and *args, mixing a positional argument with **d, errors that must still be reported, and the explicit-keyword case. It fails on master and passes with the change; check-functools.test and the full testcheck.py suite pass locally.

I used AI assistance while preparing this change; I reviewed the diff and ran the tests above.

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅