`platform.system` is not treated the same way as `sys.platform`

[dzherb]

Bug Report

It seems that conditions using platform.system() are not treated the same way as those using sys.platform. I'm not sure if this is a bug or a missing feature.

To Reproduce

import platform
import sys


def works() -> None:
    if sys.platform == "win32":
        import some_win_dependency
        some_win_dependency.do_stuff()
        return
    ...
    return

def doesnt_work() -> None:
    if platform.system() == "Windows":
        import some_win_dependency  # got [import-not-found]
        some_win_dependency.do_stuff()
        return
    ...
    return

Your Environment

• Mypy version used: 1.15.0
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):
• Python version used: 3.13

[erictraut]

The typing spec mandates that type checkers understand an expression of the form sys.platform == "win32". It doesn't mention the form platform.system() == "Windows". It also cautions against using more complex forms (such as call expressions) and expecting them to work with static type checkers. See this section of the typing spec for details.