Detect POSIX-style paths on Windows

I have a git binary installed on Windows (the MSYS2 variant, specifically) that does not understand Windows-style paths. When trying to install software using setuptools_scm, this leads to cryptic errors such as the following:

William@DESKTOP-H0PMN4M MINGW64 ~/Projects/FPGA/nmigen
$ python setup.py develop
Traceback (most recent call last):
  File "setup.py", line 10, in <module>
    setup(
  File "C:/msys64/mingw64/lib/python3.8/site-packages/setuptools/__init__.py", line 145, in setup
    return distutils.core.setup(**attrs)
  File "C:/msys64/mingw64/lib/python3.8/distutils/core.py", line 108, in setup
    _setup_distribution = dist = klass(attrs)
  File "C:/msys64/mingw64/lib/python3.8/site-packages/setuptools/dist.py", line 447, in __init__
    _Distribution.__init__(self, {
  File "C:/msys64/mingw64/lib/python3.8/distutils/dist.py", line 292, in __init__
    self.finalize_options()
  File "C:/msys64/mingw64/lib/python3.8/site-packages/setuptools/dist.py", line 740, in finalize_options
    ep.load()(self)
  File "C:/msys64/mingw64/lib/python3.8/site-packages/setuptools/dist.py", line 747, in _finalize_setup_keywords
    ep.load()(self, ep.name, value)
  File "c:/msys64/home/william/projects/fpga/nmigen/.eggs/setuptools_scm-3.5.0-py3.8.egg/setuptools_scm/integration.py", line 17, in version_keyword
    dist.metadata.version = _get_version(config)
  File "c:/msys64/home/william/projects/fpga/nmigen/.eggs/setuptools_scm-3.5.0-py3.8.egg/setuptools_scm/__init__.py", line 147, in _get_version
    parsed_version = _do_parse(config)
  File "c:/msys64/home/william/projects/fpga/nmigen/.eggs/setuptools_scm-3.5.0-py3.8.egg/setuptools_scm/__init__.py", line 103, in _do_parse
    version = _version_from_entrypoints(config) or _version_from_entrypoints(
  File "c:/msys64/home/william/projects/fpga/nmigen/.eggs/setuptools_scm-3.5.0-py3.8.egg/setuptools_scm/__init__.py", line 63, in _version_from_entrypoints
    version = _call_entrypoint_fn(root, config, ep.load())
  File "c:/msys64/home/william/projects/fpga/nmigen/.eggs/setuptools_scm-3.5.0-py3.8.egg/setuptools_scm/__init__.py", line 44, in _call_entrypoint_fn
    return fn(root, config=config)
  File "c:/msys64/home/william/projects/fpga/nmigen/.eggs/setuptools_scm-3.5.0-py3.8.egg/setuptools_scm/git.py", line 98, in parse
    wd = GitWorkdir.from_potential_worktree(config.absolute_root)
  File "c:/msys64/home/william/projects/fpga/nmigen/.eggs/setuptools_scm-3.5.0-py3.8.egg/setuptools_scm/git.py", line 33, in from_potential_worktree
    if not samefile(real_wd, wd):
  File "C:\msys64\mingw64/lib/python3.8/genericpath.py", line 100, in samefile
    s1 = os.stat(f1)
FileNotFoundError: [WinError 3] The system cannot find the path specified: '/home/William/Projects/FPGA/nmigen'

The error comes from the path git returns from the rev-parse command:

William@DESKTOP-H0PMN4M MINGW64 ~/Projects/FPGA/nmigen
$ git rev-parse --show-toplevel
/home/William/Projects/FPGA/nmigen

One potential solution is to pipe the output of git rev-parse through cygpath is we detect that the git being run is MSYS2 (or otherwise doesn’t understand Windows-style paths), as unfortunately conversion between POSIX and Windows path is an involved problem:

William@DESKTOP-H0PMN4M MINGW64 ~/Projects/FPGA/nmigen
$ git rev-parse --show-toplevel | cygpath -w -f -
C:\msys64\home\William\Projects\FPGA\nmigen

The following workaround allows me to successfully run the egg-info, develop, and install successfully (with warning: no previously-included files found matching '.travis.yaml'). Obviously this patch isn’t acceptable as-is, and this may not be the correct repo to bring this issue up, depending on the scope of supported git variants. However, I figure it’s worth a shot.

William@DESKTOP-H0PMN4M MINGW64 ~/Projects/py-packages/setuptools_scm
$ git diff
diff --git a/src/setuptools_scm/file_finder_git.py b/src/setuptools_scm/file_finder_git.py
index 8b81d2c..f68c91a 100644
--- a/src/setuptools_scm/file_finder_git.py
+++ b/src/setuptools_scm/file_finder_git.py
@@ -17,6 +17,13 @@ def _git_toplevel(path):
                 universal_newlines=True,
                 stderr=devnull,
             )
+
+            out = subprocess.check_output(
+                ["cygpath", "-w", out],
+                cwd=(path or "."),
+                universal_newlines=True,
+                stderr=devnull,
+            )
         trace("find files toplevel", out)
         return os.path.normcase(os.path.realpath(out.strip()))
     except subprocess.CalledProcessError:
diff --git a/src/setuptools_scm/git.py b/src/setuptools_scm/git.py
index afefa34..43cc6c5 100644
--- a/src/setuptools_scm/git.py
+++ b/src/setuptools_scm/git.py
@@ -27,6 +27,9 @@ class GitWorkdir(object):
     @classmethod
     def from_potential_worktree(cls, wd):
         real_wd, _, ret = do_ex("git rev-parse --show-toplevel", wd)
+        if ret:
+            return
+        real_wd, _, ret = do_ex("cygpath -w {}".format(real_wd), wd)
         if ret:
             return
         trace("real root", real_wd)

William@DESKTOP-H0PMN4M MINGW64 ~/Projects/py-packages/setuptools_scm
$

[RonnyPfannschmidt]

Can you open a pr for more detailed discussion

I believe it looks okish enough

[lazka]

We’ve patched this now in MSYS2 by calling git in a way so it outputs relative paths: https://github.com/msys2/MINGW-packages/blob/master/mingw-w64-python-setuptools-scm/0001-git-Use-show-prefix-instead-of-show-toplevel-for-fin.patch

If this is something that’s considered acceptable I can try to upstream it.