Re: [boost] [wiki] Warning Guidelines for VC

Subject: Re: [boost] [wiki] Warning Guidelines for VC
From: Paul A. Bristow (pbristow_at_[hidden])
Date: 2010-12-31 10:40:59

> -----Original Message-----
> From: boost-bounces_at_[hidden] [mailto:boost-bounces_at_[hidden]]
> On Behalf Of Stephan T. Lavavej
> Sent: Friday, December 31, 2010 2:12 PM
> To: boost_at_[hidden]
> Subject: Re: [boost] [wiki] Warning Guidelines for VC
> 
> [Michael Caisse]
> > STL's (Stephan Lavavej's) advice on the subject was to *not* use /Za
> > because it has "an extremely nasty bug".
> 
> [Beman Dawes]
> > Does anyone know if this "nasty bug" is fixed in the VC++ 2010 SP1 beta?
> 
> When I encountered that bug (valid code like vector<unique_ptr<T>>
triggers
> compiler errors under /Za; the problem is that /Za performs an
elided-copy-
> constructor accessibility check during move construction when no copy
> constructor is being called even theoretically), I asked for a fix, but
> unfortunately the resolution was "won't fix forever". I can confirm that
it will
> not be fixed in VC10 SP1 RTW, and that there are currently no plans to fix
it in
> VC11.
> 
> As a result, during VC10's development we stopped testing our C++ Standard
> Library implementation under /Za, and I no longer consider it to be a
supported
> switch. (We support almost all switches, including the headache-inducing
ones
> like /Gr and /Gz, but we have to draw the line when valid code is broken.)
> 
> I also asked for /Za to be removed from VC11, but that won't happen
either.
> (However, I was told that /Wp64, which was deprecated in VC9 and VC10,
will
> be removed from VC11. I don't think that's happened yet so I'll have to
ping a
> compiler dev about it. /Wp64 has always been broken - it suffers from
false
> positives and false negatives and interacts extremely badly with templates
- and
> it has been completely superseded by the existence of x64-targeting
compilers.)
> 
> My comments at http://blogs.msdn.com/b/vcblog/archive/2010/12/09/vs2010-
> sp1-beta-what-s-on-it-for-c-developers.aspx#10103019 and below provide a
> guaranteed-to-be-exhaustive list of the STL bugs fixed in VC10 SP1
Beta/RTW
> (there are 3 in the Beta, and no more are planned for RTW; if that changes
I'll
> post about it), and a partial list of VC fixes in the SP1 Beta (I was able
to dig up
> most of the Connect bugs that were fixed).

Well it's really good to get news from the 'horse's mouth'  - even if the
news is bad!

So it would seem that there is no reliable way to determine if any code
(including STL) is C++ Standard Conforming,
apart from trying to compile it on a non-Microsoft Standard Conforming
Compiler in strict mode?

So while many, if not most, Boost Users will deplore this on principle,
I fear we must be pragmatic and accept this, however unhappily.

Fortunately, our extensive testing schedule using all the many compilers
(using their 'strict' mode where possible) will reveal un-portability before
any final Boost release 'hits the streets'.

So unless there are other views, I propose to change the 'Dealing with
warnings guidelines' to warn that the option is 'definitely dodgy'.
(mainly by a link to this helpful post).

Although /Za might help a little during development, loading and testing on
the trunk remains the definitive test of portability.

Thanks

Paul

---
Paul A. Bristow,
Prizet Farmhouse, Kendal LA8 8AB  UK
[phone]  07714330204
pbristow_at_[hidden]