[LLVMdev] [RFC] Raising minimum required Visual Studio version to 2013 for trunk

[Renato Golin]

On 22 August 2014 00:48, Aaron Ballman <aaron at aaronballman.com> wrote:
> We told the community less than nine months ago (when we made the
> C++11 switch) that we would support the last two versions of MSVC. Now
> we're saying "only the latest version, because it has nice things."

I don't see it this way. We need a compiler on all platforms that can
conform to the same level of the standards. In most platforms, that's
GCC and Clang, on Windows, that's also MSVC.

The problem here is that Linux and Mac developers will test their code
on multiple combinations of { Linux, Mac } x { x86, x86_64, ARM,
AArch64 } and it'll work perfectly, until it reaches Windows and
breaks because the compiler can't handle it.

Solving this problem is not trivial, and relying on buildbots to tell
us what's wrong promotes a culture of trial and error that makes it
impossible to control the source at any level (ex reverting bugged
commits, or applying them back again).


> That would make sense if those nice things were something we couldn't
> live without, or if there was a long delay for a new release of MSVC.
> Neither of those things seem to be the case, so I'm not certain why we
> would change our developer policy on three day's notice.

 We're finding the hard way that it could have been a lot better if
MSVC 2012 were actually a modern compiler to begin with. We haven't
changed the minimum requirement anywhere else, and still, it's MSVC
that is breaking up. That's a clear sign that MSVC 2012 is *not*
compatible (feature-wise) with all our other minimum requirements.

IIRC, we "accepted" MSVC 2012 as the minimum requirement due to
pressure, not because we thought it was a good idea and we said it
would have to move faster than the others because of the sheer lack of
functionality. Now it's past 3.5 release and 3.6 will probably come
out in 2015, the sooner we start the move to a more modern MSVC, the
better it'll be when we actually release 3.6.

I think Chandler's idea to break it now and see how it goes, by
changing only the make files, is a good one. At least we'll make all
the problems visible, and will be able to tackle them one by one,
instead of waiting for some people to chime in, people that haven't
been involved yet?

I also believe that we need to answer Alex's questions before
anything. We can't just guess, as we're talking here of a possible
massive incompatibility problem on millions of software out there (and
the games we play!!), so that's a critical issue! :)

But other than that, stakeholders should have been doing their
homework and trying 2013 ever since 9 months ago. It's most definitely
not 3 days ago.

cheers,
--renato