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

[R. David Murray]

On Sun, 26 Oct 2014 00:19:44 +0200, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Sun, 26 Oct 2014 09:06:36 +1100
> Chris Angelico <rosuav at gmail.com> wrote:
> > On Sun, Oct 26, 2014 at 8:59 AM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> > > How do you know this isn't a problem, since you haven't *tested* with
> > > MSVC?
> > > Why on Earth would you want to test your PEP work with an unsupported
> > > Windows compiler and runtime, rather than with the officially supported
> > > compiler and runtime?
> > 
> > This discussion revolved around supporting MinGW in addition to MSVC.
> > If it had been supported when I was doing that, I could have spun
> > myself up a Windows build and tested it.
> 
> My point is that your "Windows build" would not have the same behaviour
> as a MSVC-produced Windows build, and so testing it with it would not
> certify that your code would actually be compatible with genuine
> MSVC builds of CPython, which we will not stop supporting.

While true, I don't think that matters for Chris' point.  Given only the
ability to build with the MSVC toolchain, his code (which might even be
pure python for the purposes of this discussion) would not get tested on
Windows until committed and run by the buildbots.  If he could build
CPython using MinGW, he would, and would test his code on Windows.  Even
if there are C components and MSVC/MinGW compatibility issues are
revealed when the buildbots eventually run the code, still the number of
bugs present would probably be lower if he had tested it on Windows
than if he hadn't.

I know I for one do not generally test patches on Windows because I
haven't taken the time to learn how to build CPython on it.  Sure, I
could test pure python changes by applying patches to an installed
Python, but that's an ongoing pain and I'd rather learn to build CPython
on Windows and get to use the normal hg tools.

If I could use a more linux-like toolchain to build CPython on windows,
I would doubtless do much more testing on windows for stuff where I
think windows might behave differently (and I might look at more Windows
bugs...though frankly there are plenty of bugs for me to look at without
looking at Windows bugs).

This is not necessarily a compelling argument for MinGW support.
However, it *is* a valid argument, IMO.

Note: it can be made even less compelling by making it a lot easier to
build CPython on Windows without having an MSVC license (which I think
means not using the GUI, for which I say *yay* :).  I think Zach Ware
has been working on improving the Windows build process, and I keep
meaning to give it a try...

--David