The current logic for detecting cygwin is:

• if sys.platform == "win32", then it's not cygwin
• if the passed-in git executable is None, then it's not cygwin git
• finally, is there a uname executable in the same folder as the git executable, and if so, does the output of that command include "CYGWIN"? if so, then it's cygwin

In the python 3.7 docs for sys.platform, Cygwin systems have sys.platform == "cygwin". Since Python 3.7 is the oldest version still supported by GitPython, it stands to reason that we can rely on that being true for all supported Python versions.

The logic I propose is:

• if the git executable you passed in is None, it's not cygwin git
• if sys.platform == 'cygwin', then it's cygwin git

This is simple enough for a single expression, so I replaced the body of the is_cygwin function with that expression and removed is_cygwin_git and friends completely.

I don't know if there's such a thing as sys.platform == 'cygwin' and the git not being cygwin git, but if there is, I don't think the existing code deals with that anyway, so this seems to return the same result and would fail in the same way.