[ty] Treat lambda functions as instances of types.FunctionType

[lipefree]

Summary

Fixes astral-sh/ty#567.

Since lambda functions are instance of types.FunctionType, we should be able to access to attribute such as __code__, __name__ and more. With this PR, we will have the following type and no more errors :

from typing import reveal_type

x = lambda y: y

reveal_type(x.__code__)  # revealed: CodeType

Test Plan

I have added mdtests, but since I am not familiar with attributes of types.FunctionType, my tests may be either too redundant or not exhaustive enough.

[github-actions]

mypy_primer results

Changes were detected when running on open source projects

static-frame (https://github.com/static-frame/static-frame)
- error[unresolved-attribute] static_frame/core/util.py:571:5: Unresolved attribute `__name__` on type `(rhs, lhs, func=Any) -> Unknown`.
- Found 1944 diagnostics
+ Found 1943 diagnostics

bokeh (https://github.com/bokeh/bokeh)
+ error[invalid-assignment] src/bokeh/core/templates.py:112:1: Object of type `dict[str, () -> Unknown]` is not assignable to `dict[str, () -> Template]`
- Found 951 diagnostics
+ Found 952 diagnostics

sphinx (https://github.com/sphinx-doc/sphinx)
- error[unresolved-attribute] sphinx/ext/autodoc/preserve_defaults.py:28:16: Type `() -> Unknown` has no attribute `__name__`
- Found 657 diagnostics
+ Found 656 diagnostics

dd-trace-py (https://github.com/DataDog/dd-trace-py)
- error[unresolved-attribute] ddtrace/debugging/_signal/utils.py:227:38: Type `((Any, /) -> bool) | ((_) -> Unknown)` has no attribute `__name__`
- error[unresolved-attribute] ddtrace/debugging/_signal/utils.py:257:38: Type `((Any, /) -> bool) | ((_) -> Unknown)` has no attribute `__name__`
- error[unresolved-attribute] ddtrace/debugging/_signal/utils.py:313:41: Type `((Any, /) -> bool) | ((_) -> Unknown)` has no attribute `__name__`
- error[unresolved-attribute] ddtrace/debugging/_signal/utils.py:332:34: Type `((Any, /) -> bool) | ((_) -> Unknown)` has no attribute `__name__`
- error[unresolved-attribute] ddtrace/debugging/_signal/utils.py:358:37: Type `((Any, /) -> bool) | ((_) -> Unknown)` has no attribute `__name__`
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:227:38: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:257:38: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:313:41: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:332:34: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:358:37: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
- error[unresolved-attribute] tests/tracer/test_writer.py:311:34: Type `(*args) -> Unknown` has no attribute `__get__`
- Found 6861 diagnostics
+ Found 6860 diagnostics

sympy (https://github.com/sympy/sympy)
- error[unsupported-operator] sympy/codegen/tests/test_applications.py:23:17: Operator `<` is not supported for types `Variable` and `Variable`
- error[unresolved-attribute] sympy/tensor/array/array_comprehension.py:342:58: Type `() -> Unknown` has no attribute `__name__`
- Found 18575 diagnostics
+ Found 18573 diagnostics

[AlexWaygood]

+ error[invalid-assignment] src/bokeh/core/templates.py:112:1: Object of type `dict[str, () -> Unknown]` is not assignable to `dict[str, () -> Template]`

This error is occuring because dict is invariant: https://github.com/bokeh/bokeh/blob/7d6cedea470cb68f25afd126a29a45370c08f443/src/bokeh/core/templates.py#L112-L127. Bidirectional inference would fix this.

+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:227:38: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:257:38: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:313:41: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:332:34: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound
+ warning[possibly-unbound-attribute] ddtrace/debugging/_signal/utils.py:358:37: Attribute `__name__` on type `((Any, /) -> bool) | ((_) -> Unknown)` is possibly unbound

These are because we do not infer Callable types created from Callable type expressions as being function-like. Whether or not we should do that is a complicated question that's discussed in other issues.

So all the primer hits here look good to me!

[AlexWaygood]

Thank you!