Compile error on Fedora 28, gcc 8.1.1 (aida.hh)

[ngeiswei]

On Fedora 28, gcc 8.1.1, I getting the following compiling error

../aidacc/aida.hh: In instantiation of ‘struct Aida::Has__accept__<std::__cxx11::basic_string<char>, Bse::PspecVisitor, void>’:
../aidacc/visitor.hh:62:23:   required by substitution of ‘template<class A, typename std::enable_if<((((! Aida::Has__accept__<A, Bse::PspecVisitor, void>::value) && (! std::is_base_of<std::__cxx11::basic_string<char>, T>::value)) && (! Aida::DerivesVector<Vector>::value)) && std::is_class<A>::value), bool>::type <anonymous> > void Aida::VisitorDispatcher<Bse::PspecVisitor>::operator()<A, <enumerator> >(A&, Aida::VisitorDispatcher<Bse::PspecVisitor>::Name) [with A = std::__cxx11::basic_string<char>; typename std::enable_if<((((! Aida::Has__accept__<A, Bse::PspecVisitor, void>::value) && (! std::is_base_of<std::__cxx11::basic_string<char>, T>::value)) && (! Aida::DerivesVector<Vector>::value)) && std::is_class<A>::value), bool>::type <anonymous> = <missing>]’
bstapi_interfaces.hh:221:15:   required from ‘void Bst::SrvT_GConfig::__accept__(Visitor&) [with Visitor = Bse::PspecVisitor]’
../sfi/sfivisitors.hh:306:3:   required from ‘SfiRecFields Bse::sfi_pspecs_rec_fields_from_visitable(Visitable&) [with Visitable = Bst::SrvT_GConfig]’
bstgconfig.cc:23:90:   required from here
../aidacc/aida.hh:166:73: error: ‘class std::__cxx11::basic_string<char>’ has no member named ‘__accept__’
 struct Has__accept__<T, V, void_t< decltype (std::declval<T>().template __accept__<V> (*(V*) NULL)) >> : std::true_type {};
                                              ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~

[tim-janik]

Hm, I'm not seeing that with g++-5 or g++-7.3.0. Also not with clang++-4, 5 or 6 (clang requires recent master though).

I'll see if I can get my hands on g++-8 in the next couple days...

[Teteros]

Getting this as well on gcc 8.2.1 (Arch linux)
EDIT: Does seem to compile with clang7 but opened a ticket for seperate build issue #86

[tim-janik]

I managed to reproduce this with g++ (GCC) 8.1.1 20180712 from Fedora-28.

But it looks like a gcc SFINAE bug to me, it treats a substitution failure as error, even though an alternative substitution exists. All clang versions and gcc < 8 compile this correctly.

it's not too easy to isolate though, I might give this another shot another day to involve the compiler guys.

@swesterfeld do you have gcc >= 8 and can weigh in on this?

[tim-janik]

Managed to isolate a test case, g++ bug report can be found here:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87748

[tim-janik]

There's no easy workaround for the g++-8.2 SFINAE bug, the code portion that triggers this is vital for the function calls between the UI and the sound engine. So, unless g++-8.3 fixes this and Fedora-28 decides to upgrade and ship, g++-8.3, Fedora-28 builds can unfortunately not be supported.

However I've now created https://github.com/tim-janik/beast/blob/master/misc/Dockerfile.fedora27 and added it to travis-ci, so we see future build issues on Fedora.

Also, since recently, we're building Beast AppImage binaries on Ubuntu-18.04, which have been tested to work well under Fedora-28, these can be found here:
https://bintray.com/beast-team/testing/Beast-AppImage

The AppImage binaries will be announced more broadly with the next release.