Preserve the class type through proxy_for_class (#418)

[rahul188]

Fixes #418.

proxy_for_class was annotated (typ: Type, varname: str) -> object, so callers got back something with no attributes and had to cast or silence mypy to use it.

The change

-def proxy_for_class(typ: Type, varname: str) -> object:
+def proxy_for_class(typ: Type[_T], varname: str) -> _T:

reusing the _T already defined in core.py. This is a pure annotation change — no runtime behavior differs.

The annotation matches what the function already does: the main path returns WithEnforcement(cls)(*args.args, **args.kwargs), an instance of the requested class. The parameterized-generic case works out too, since mypy types Container[int] in expression position as type[Container[int]], so _T binds to Container[int] and the result keeps its parameter.

The one place needing help is the TypedDict branch, which returns a dict comprehension. A TypedDict instance is a dict at runtime, so the value genuinely satisfies the declared return type, but mypy can't connect that through _T. I used a cast with a comment there rather than widening the signature back out — the alternative would give up the improvement for every other class to accommodate one branch.

What pins it

core_test.py carried three # type: ignore[attr-defined] comments — the exact workaround the issue describes:

assert isinstance(obj.value, SymbolicInt)   # type: ignore[attr-defined]
assert isinstance(obj.first, SymbolicInt)   # type: ignore[attr-defined]
assert isinstance(obj.second, LazyIntSymbolicStr)  # type: ignore[attr-defined]

They are removed. Since mypy runs over all Python files via the pre-commit hook, those lines now act as the regression check for this signature — verified by reverting core.py and leaving the tests as-is:

crosshair/core_test.py:867: error: "object" has no attribute "value"  [attr-defined]
crosshair/core_test.py:882: error: "object" has no attribute "first"  [attr-defined]
crosshair/core_test.py:883: error: "object" has no attribute "second"  [attr-defined]

With the change, mypy --ignore-missing-imports --scripts-are-modules crosshair/core.py crosshair/core_test.py reports Success: no issues found.

Testing

• crosshair/core_test.py: 95 passed, 3 skipped.
• black --check and isort --check-only clean on both files.
• flake8 reports the same three pre-existing F824 warnings in core.py before and after; nothing new.

[pschanely]

Lovely. Thank you!