Python broke in v2.5.0

The release v2.5.0 broke running Python in GH Actions with under msys, it worked in 2.4.2.

Our workflow: https://github.com/cocotb/cocotb/blob/1123973ed6979f89b8e1cb8785d5ae7c425d2908/.github/workflows/regression-tests.yml#L334-L371

Python aborts execution right after start with the following message:

Python path configuration:
  PYTHONHOME = 'D:/a/_temp/msys/msys64/mingw64'
  PYTHONPATH = (not set)
  program name = 'D:/a/_temp/msys64/mingw64/bin/python.exe'
  isolated = 0
  environment = 1
  user site = 1
  import site = 1
  sys._base_executable = 'D:/a/_temp/msys64/mingw64/bin/python.exe'
  sys.base_prefix = 'D:/a/_temp/msys/msys64/mingw64'
  sys.base_exec_prefix = 'D:/a/_temp/msys/msys64/mingw64'
  sys.platlibdir = 'lib'
  sys.executable = 'D:/a/_temp/msys64/mingw64/bin/python.exe'
  sys.prefix = 'D:/a/_temp/msys/msys64/mingw64'
  sys.exec_prefix = 'D:/a/_temp/msys/msys64/mingw64'
  sys.path = [
    'D:/a/_temp/msys/msys64/mingw64/lib/python39.zip',
    'D:/a/_temp/msys/msys64/mingw64/lib/python3.9',
    'D:/a/_temp/msys/msys64/mingw64/lib/python3.9/lib-dynload',
    '',
  ]
Fatal Python error: init_fs_encoding: failed to get the Python codec of the filesystem encoding
Python runtime state: core initialized
ModuleNotFoundError: No module named 'encodings'

There’s much more information available at https://github.com/cocotb/cocotb/issues/2739

The most likely reason for this change in behavior seems to be like https://github.com/msys2/setup-msys2/pull/163. Do you have any idea what’s going on?

Note PYTHONHOME is referring to (as far as I read the PR) the “old” installation path, ‘D:/a/_temp/msys/msys64/mingw64’, while the Python binary is in the new installation path.

[lazka]

Ah, I see. Or we could use a different path in autobuild.

[ktbarrett]

@lazka Read this: https://docs.python.org/3/using/cmdline.html#envvar-PYTHONHOME. prefix and PYTHONHOME should be one in the same. We put that line in place based on the following recommendation. PYTHONHOME and the path to the Python standard library can be deduced from the Python executable, but apparently not necessarily from libpython, so you are expected to help it out. The only way we can do that is by invoking Python and asking it what it thinks PYTHONHOME should be.