[Python-Dev] Status of C compilers for Python on Windows

[Tony Kelman]

I'm several weeks late to this discussion, but I'm glad to see that it
happened. I'm not a Python developer, and barely a user, but I have several
years of daily experience compiling complicated scientific software cross-
platform, particularly with MinGW-w64 for Windows. The Python community,
both core language and scientific package developers and users, needs to
act here. The problem is bad and getting worse. Luckily much of the work
to start solving it has already been done in bits and pieces, it needs
coordination and participation to come to a conclusion.

> Cross compilation is a valid issue, but I hope that build services like
> Appveyor also help out here. There is regular talk about the PSF/PyPI
> providing something similar

AppVeyor is better than nothing (I've been using it since beta), but it's
a far cry from build services and package management as the Linux world
knows them. Obtaining and setting up build dependencies quickly and
repeatably, and finishing the build of a complicated piece of software
such as CPython, or NumPy, SciPy, Julia (where most of my recent expertise
lies), etc. on a small single-core VM with limited memory and a restrictive
time limit is often not possible. These problems are solved within Linux
infrastructure like Koji, Open Build Service, buildd, etc.

MinGW-w64 is a mature, well-tested toolchain that is very capable of cross-
compiling a wide variety of libraries from Linux to Windows, in addition to
building conventionally on Windows for Windows. The MSYS2 collection of
MinGW-w64-compiled packages (https://github.com/Alexpux/MINGW-packages) has
been mentioned. Linux distributions including
- Fedora https://admin.fedoraproject.org/pkgdb/packages/mingw%2A/
- openSUSE https://build.opensuse.org/project/show/windows:mingw:win32
- Arch https://aur.archlinux.org/packages/?K=mingw
and others have projects for providing many hundreds of open-source
packages compiled for Windows. Debian has the cross-compilers available but
not many packages yet (https://packages.debian.org/search?keywords=mingw).

As a developer of a (compiled) open-source library or application, wouldn't
you love to be able to build binaries on Linux for Windows? With some work
and build system patches, you can. For many projects it's a simple matter of
./configure --host=x86_64-w64-mingw32. Not with CPython though. CPython is
only included in 2 of the above MinGW-w64 distribution projects, MSYS2 and
Arch. This is possible with a very, very long set of patches, many of which
have been submitted by Roumen Petrov to the Python bug tracker - see
http://bugs.python.org/issue17605 and other issues linked therein. Roumen
has done a huge amount of work, and he and others who consider the MinGW-w64
compiler important will continue to do so. (Thanks a million Roumen!)

> I could step in as maintainer for Cygwin and builds based on GCC using
> mingw* APIs.
>
> Regards,
> Roumen Petrov

A maintainer has volunteered. Others will help. Can any core developers
please begin reviewing some of his patches? Even if just to say they need
to be rebased. The lack of responses on the bug tracker is disheartening
from an outside perspective. The pile of patches accumulating in external
MinGW packaging projects is tantamount to a fork of CPython. It won't go
away since there are dedicated packagers working to keep their MinGW-w64
builds functional, even in the ad-hoc current state. The patches continue
piling up, making it more difficult for everyone - except for the core
Python developers if they continue to ignore the problem. Bring the people
working on these patches into the fold as contributors. Review the patches.
It would make Python as a language and a community even more diverse and
welcoming.

> Deprecate/remove support for compiling CPython itself with compilers
> other than MSVC on Windows

I'm not alone in thinking that this would be a bad idea. MSVC can continue
to be the default compiler used for Python on Windows, none of Roumen's
patches change that. They would merely open up the choice for packagers and
users to build CPython (and extension modules, thanks to separate patches)
with alternate compilers, in cross-compilation or otherwise.

Sincerely,
Tony