False positive TCH003 for singledispatchmethod

[last-partizan]

This is almost the same as #11520 , but for @singledispatchmethod

from __future__ import annotations

from collections.abc import MutableMapping
from functools import singledispatchmethod
from typing import Any


class Foo:
    @singledispatchmethod
    def foo(self, x: Any) -> int:
        raise NotImplementedError

    @foo.register
    def _(self, x: MutableMapping) -> int:
        return 0

> ruff check --select TCH app/test.py

app/test.py:3:29: TCH003 Move standard library import `collections.abc.MutableMapping` into a type-checking block
  |
1 | from __future__ import annotations
2 |
3 | from collections.abc import MutableMapping
  |                             ^^^^^^^^^^^^^^ TCH003
4 | from functools import singledispatchmethod
5 | from typing import Any
  |
  = help: Move into type-checking block

Found 1 error.
No fixes available (1 hidden fix can be enabled with the `--unsafe-fixes` option).

> python --version
Python 3.12.7
> ruff --version
ruff 0.7.1

[MichaReiser]

I don't think I understand this issue. Could you explain me why MutableMapping can't be moved into a type checking block?

[last-partizan]

Because @simgledispatchmethod is using runtime types, just like normal @singledispatch from #11520

Example:

> python /tmp/test.py
Traceback (most recent call last):
  File "/tmp/test.py", line 10, in <module>
    class Foo:
  File "/tmp/test.py", line 15, in Foo
    @foo.register
     ^^^^^^^^^^^^
  File "/usr/lib/python3.12/functools.py", line 939, in register
    return self.dispatcher.register(cls, func=method)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/functools.py", line 877, in register
    argname, cls = next(iter(get_type_hints(func).items()))
                             ^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/typing.py", line 2310, in get_type_hints
    hints[name] = _eval_type(value, globalns, localns, type_params)
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/typing.py", line 415, in _eval_type
    return t._evaluate(globalns, localns, type_params, recursive_guard=recursive_guard)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/typing.py", line 947, in _evaluate
    eval(self.__forward_code__, globalns, localns),
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "<string>", line 1, in <module>
NameError: name 'MutableMapping' is not defined