Re: [cxx-gtk-utils-general] Build failure on armv5tl

[Chris V. <ch...@cv...>]

On Thu, 12 May 2016 13:14:22 +0100
Chris Vine <ch...@cv...> wrote:
> On Thu, 12 May 2016 12:09:26 +0100
> Barry Jackson <zen...@ze...> wrote:
> > Ah - seems I attached the wrong file - this is correct.
> > 
> > Barry
> >   
> 
> It looks like a compiler bug.  The error is first reported in line
> 522 of tests/test_task_manager.cpp, and says that std::future<int>
> is an incomplete type, when clearly it is complete.  It looks as if
> the compiler cannot find the 'future' class in the std namespace.  It
> should be able to do so, because the <future> header is included.
> 
> You could try including a 'using namespace std;' statement after the
> 'using namespace Cgu;' in the file test_task_manager.cpp.  If that
> fixes it then it is definitely a compiler bug.
> 
> The build seems to be using gcc-5.3.1, which should be new enough but
> is not actually a gnu release, I think (gnu has only released
> gcc-5.3.0 in the 5.3 series).

On looking at it further, it seems that std::future was not supported
by gcc-4.8 on armv5 because of the lack of an appropriate atomic
instruction: the debian error report at
https://gcc.gnu.org/ml/gcc/2014-07/msg00001.html is very similar to
yours.

So it looks as if that may remain the case with gcc-5.3 (bummer).  If so
it looks like a big miss and you are going to find an increasing number
of C++ packages failing to build for this reason, if that is the
reason: std::future is hardly ground-breaking.  amd64 seems to be OK.

You may have better luck with clang and their libc++, I don't know.
You could also look and see if it is fixed in gcc-6.1 (probably not).

Alternatively, if you want a distributable package, you could just omit
the tests by not having your build system call 'make check' or 'make
tests'.  Happily the code in question in c++-gtk-utils is templated and
so not actually instantiated unless it is used (as it is by the test
suite).  Of course if users actually try calling a function returning a
std::future object they would then get a compile-time error similar to
yours, but that is a separate issue, and one which they are probably
aware of if using armv5.

Chris