Re: [boost] [range] concept checks break chained range adaptors

Subject: Re: [boost] [range] concept checks break chained range adaptors
From: Jürgen Hunold (jhunold_at_[hidden])
Date: 2014-06-15 10:46:41

Hi Neil,

Am Samstag, 14. Juni 2014, 15:27:05 schrieb Neil Groves:
> Hi!
> 
> On Sat, Jun 14, 2014 at 2:26 PM, Jürgen Hunold <jhunold_at_gmx.eu> wrote:
> > Hi Neil,
> > 
> > the fix for #9851 broke some of our code. We use chained range adaptors
> > like
> 
> This fix simply enables BOOST_RANGE_CONCEPT_ASSERT. I had previously
> disabled this checking on more compilers than I should have. This was
> motivated to get code up and running on compilers that I didn't have access
> to. I have since had users have a number of difficulties due that have been
> difficult to diagnose due to having concept checking disabled. This is
> particularly the case on later versions of Clang where the C++ support is
> now excellent.
> 
> I therefore do not wish to revert the commit for reasons:
> 1. Any specific problem with particular compilers can be worked around by
> simply disabling BOOST_RANGE_CONCEPT_ASSERT in boost/range/config.hpp
> 2. I will find ways of making concept assertions work by changing them in
> the cases where there are problems
> 3. I will specifically disable concept assertions for problems for which I
> fail to find solutions

Well, I don't want you to revert those commits. I'm glad to have found  the 
commit(s) which caused regressions here.

> > Full testcase and error message attached.
> > This compiles and works with 1.55.0. git bisect shows that this fails to
> > compile from
> > 5f2560f - Ticket 9851 - adaptors should perform concept check assertions.
> > for gcc and for clang starting with
> > e43796c - allow clang to use Range Concepts despite reporting GCC 4.2.
> > msvc-12.0 fails, too. gcc-4.8.2 and clang-3.5 (trunk) for the record.
> 
> I really appreciate the thorough report. I shall look at this problem over
> the next couple of days and update the Trac ticket to report if I believe I
> can get this fixed for the 1.56 release. My initial reading of this issue
> is that the problem is with the actual Concepts disallowing valid use
> cases. Therefore the code before 5f2560f would perhaps have worked on the
> compilers you were using but would have failed elsewhere. Let's see if we
> can get it working everywhere.

Well, the test case (and the original code) works with gcc-4.8.x, clang 3.4 
and 3.5 and at least msvc-12.0 with Boost 1.55.0 

> My assumption is that by a minor edit to boost/range/config.hpp you can get
> back up and running. Please confirm/deny this assumption.

Sorry, you lost me there. I can see no concept check related #defines there. 
Can you clarify this?

> > Any chance to get this fixed for 1.56.0 ?
> 
> I shall try to within the constraints of the release schedule. It is
> starting to get a little tight. Hopefully this will only require changes
> that are backward compatible. I certainly shall provide you with a solution
> although it might require a small patch if I miss the release window.

I would have spotted this earlier if clang would not disguise as gcc-4.2 (see 
e43796c) and I'm mostly using clang these days :-(. So no need to hurry, I can 
apply patches to our internal repository for Boost any time ;-)
 
> Sorry for the inconvenience caused by these changes. I hope I can convince
> you that it is part of a march toward a general improvement so that users
> can more frequently enjoy the benefits of concept checking.

No need for excuses, I fully understand your motivation :-) Improvements are 
always good in the long term. Short term hiccups are to be expected. This is 
not the first nor will be the last regression our large codebases have caught 
:-) The main reason I'm regularly using boost's develop branch is to catch 
those errors before they get released.

Yours,

Jürgen
-- 
* Dipl.-Math. Jürgen Hunold  ! 
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