Re: [boost] Boost and clang under Windows

Subject: Re: [boost] Boost and clang under Windows
From: Beman Dawes (bdawes_at_[hidden])
Date: 2013-09-29 14:52:34

On Sun, Sep 29, 2013 at 1:40 PM, Edward Diener <eldiener_at_[hidden]>wrote:

> On 9/29/2013 1:21 PM, Andrey Semashev wrote:
>
>> On Sunday 29 September 2013 12:59:27 Edward Diener wrote:
>>
>>> First off I am not of course proposing any changes to the upcoming
>>> release build of Boost 1.55 for clang under Windows.
>>>
>>> It turns out that clang under Windows, possibly to support the ability
>>> to use Windows header file, becomes another compiler which defines
>>> _MSC_VER. I believe the Intel compiler also does this but there may be
>>> some others.
>>>
>>> However clang is a much more strictly conforming to the C++ standard
>>> compiler than VC++ and does not have VC++'s quirks. This presents a
>>> problem in Boost.
>>>
>>> The Boost header files have numerous places where testing the macro
>>> _MSC_VER produces slightly different behavior based on the fact that the
>>> code is being used by VC++ or a compiler with the same behavior as VC++.
>>> But clang does not have the same behavior as VC++ despite defining
>>> _MSC_VER.
>>>
>>> Can I go ahead and change some of these situations as necessary to get
>>> clang under Windows to work properly with Boost code ?
>>>
>>
Please do not do that. I had face-to-face meetings this week with Chandler
Carruth
and others working on Clang for Windows. They are depending on Boost's
tests to find bugs in Clang's emulation of Visual C++, and if you work
around their bugs it will deprive them of a valuable testing tool.

>
>>> The usual change will be to test not only _MSC_VER but also that
>>> __clang__ is not defined for keeping the current implementation which
>>> assumes a VC++ compatible compiler with VC++ behavior. I am willing to
>>> make those changes in 'trunk' and keep an eye out for any significant
>>> failures in unit tests for our current regression tests.
>>>
>>
Please do not do that.

>
>>> I have already made a slight change to Boost PP config.hpp on 'trunk' so
>>> that clang for Windows will pass the preprocessor tests.
>>
>>
Please revert that change. That preprocessor problem was one of the
specific examples they cited where they are hoping to achieve VC++
compatibility. They really want boost tests to fail until compatibility is
achieved, and then to detect any regressions if compatibility is lost.

I don't think it occurred to them or to me during the discussions that
anyone would try to workaround failures before the clang folks had a chance
to introduce Microsoft compatibility fixes. I'll get back to Chandler with
a request for a public statement of their plan.

He asked me to post a request for help on the Boost list, but it may take
several days. It takes quite a while to work through do lists after a C++
committee meeting.

--Beman