Ultra slow path conversion

[dragon-archer]

I've encountered several ultra slow path conversions under MSYS2, see the following example:

$ which python
/clang64/bin/python

$ time python -c "import sys; print(sys.argv)" "/c"
['-c', 'C:/']
python -c "import sys; print(sys.argv)" "/c"  0.01s user 0.00s system 37% cpu 0.040 total

$ time python -c "import sys; print(sys.argv)" "/\c"
['-c', '//c']
python -c "import sys; print(sys.argv)" "/\c"  0.01s user 0.00s system 0% cpu 2.753 total

I've tried the example several times under different shells (bash, zsh, etc.), seems the problem comes from msys2 itself

P.S.: my MSYS2_ARG_CONV_EXCL is unset

[dragon-archer]

Seems that the problem comes from cygpath

$ time cygpath -m '/c'
C:/
cygpath -m '/c'  0.00s user 0.01s system 65% cpu 0.023 total

$ time cygpath -m '/\c'
//c
cygpath -m '/\c'  0.01s user 0.00s system 0% cpu 2.734 total

Some version info

$ cygpath --version
cygpath (cygwin) 3.6.5
Path Conversion Utility
Copyright (C) 1998 - 2025 Cygwin Authors
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ pacman -Qi msys2-runtime
Name            : msys2-runtime
Version         : 3.6.5-1
Description     : Posix emulation engine for Windows
Architecture    : x86_64
URL             : https://www.cygwin.com/
Licenses        : GPL
Groups          : None
Provides        : None
Depends On      : None
Optional Deps   : None
Required By     : base
Optional For    : None
Conflicts With  : catgets  libcatgets  msys2-runtime-3.6
Replaces        : catgets  libcatgets  msys2-runtime-3.6
Installed Size  : 6.48 MiB
Packager        : CI (msys2/msys2-autobuild/55384653/18410076696)
Build Date      : Fri Oct 10 22:51:03 2025
Install Date    : Sat Dec 13 17:28:08 2025
Install Reason  : Explicitly installed
Install Script  : No
Validated By    : Signature