dbusmenu-qt5 build failure on 10.7 and 10.8 buildbots because of using libstdc++

[Mojca Miklavec]

On 6 October 2016 at 14:43, Ryan Schmidt wrote:
>> On Oct 6, 2016, at 7:35 AM, Mojca Miklavec wrote:
>>
>> It works without https://trac.macports.org/wiki/LibcxxOnOlderSystems
>> (= setting libc++ to become your default stdlib globally). But the
>> port in question most likely still needs libc++.
>>
>> Read as: if you use the cxx11 PortGroup and use a default installation
>> of MacPorts, the port won't compile. But you can still require libc++
>> for this individual port and it might compile and work.
>>
>> Using the cxx11 PortGroup is desired/absolutely needed when a port has
>> many dependencies that need a compatible stdlib as the app would crash
>> otherwise. It is not needed for "standalone" apps that don't need to
>> communicate to their dependencies via some C++ API (or when
>> dependencies use the same stdlib, like qt5 which switched to libc++
>> anyway).
>
> You're right. You should only force libc++ (without using the cxx11 portgroup) if the port
>
> a) requires C++11 (or for some other reason requires libc++), and
> b) does not depend on any C++ libraries, and

Generally true. But this can be relaxed a bit: "or if dependent
libraries with C++ api are also guaranteed to use libc++".

> c) does not provide any C++ libraries

Are you talking about the PortGroup (like the qt5 PortGroup) or about
individual ports?

In case of the latter: why is this relevant for the port in question?
Doesn't that only affect dependent ports? And dependent ports don't
know that their dependency included the c++11 PortGroup.

> Is that the case for Qt5? It is the case for mongodb, so I've done it there. Qt5 provides tons of libraries that other programs are expected to use, and they seem to link to the C++ library, so I don't think we can just force Qt5 to libc++ and hope things will work; they won't.

One case of a problematic port is gnuplot. If one wants to use Qt5
(which is optional and disabled by default), gnuplot has to be
compiled with libc++, but then wxWidgets should either not be enabled
or it should be compiled against libc++ too. I simply didn't add that
complex logic into the Portfile.

All I did was a lame warning (but luckily not many people bother
installing the qt5 variant, or at least not users of legacy systems):

variant qt5 conflicts qt description "Enable qt terminal with Qt 5" {
    if { ${configure.cxx_stdlib} ne "libc++" } {
        ui_warn "Gnuplot should be compiled against libc++ if you want
to use Qt 5."
    }

Mojca