Re: compilation of mellowplayer fails on Fedora 30 with gcc-9.0.1 - error: redundant move in return statement [-Werror=redundant-move]

[J. Scheurich]

the compilation of mellowplayer-3.5.1 with gcc-9.0.1 fails on Fedora 30,
see the build.log [1]
>  Fedora Bugzilla [2] - -Wredundant-move gives false positives in C++11
> mode
>
>  [1] https://kojipkgs.fedoraproject.org//work/tasks/2212/32602212/build.log 
BUILDSTDERR:
/builddir/build/BUILD/MellowPlayer-402e336880f94853a541fc3e773e593b584fe8e0/src/3rdparty/boost-di-extensions/Factory.hpp:31:24:
  required from here
BUILDSTDERR:
/builddir/build/BUILD/MellowPlayer-402e336880f94853a541fc3e773e593b584fe8e0/src/3rdparty/boost-di-extensions/Factory.hpp:45:32:
error: redundant move in return statement [-Werror=redundant-move]
BUILDSTDERR:
/builddir/build/BUILD/MellowPlayer-402e336880f94853a541fc3e773e593b584fe8e0/src/3rdparty/boost-di-extensions/Factory.hpp:45:32:
note: remove 'std::move' call
BUILDSTDERR: cc1plus: error: unrecognized command line option
'-Wno-c++1z-extensions' [-Werror]
BUILDSTDERR: cc1plus: error: unrecognized command line option
'-Wno-unused-private-field' [-Werror]
BUILDSTDERR: cc1plus: all warnings being treated as errors
BUILDSTDERR: make[2]: *** [src/main/CMakeFiles/MellowPlayer.dir/build.make:150:
src/main/CMakeFiles/MellowPlayer.dir/Program.cpp.o] Error 1
BUILDSTDERR: make[1]: *** [CMakeFiles/Makefile2:515:
src/main/CMakeFiles/MellowPlayer.dir/all] Error 2
BUILDSTDERR: make: *** [Makefile:133: all] Error 2
RPM build errors:
BUILDSTDERR: error: Bad exit status from /var/tmp/rpm-tmp.CD4l4Z (%build)
BUILDSTDERR:     Bad exit status from /var/tmp/rpm-tmp.CD4l4Z (%build)
Child return code was: 1
EXCEPTION: [Error()]
Traceback (most recent call last):

it looks lie the options  -Wno-c++1z-extensions and
-Wno-unused-private-field' are wrong

...

UILDSTDERR:
/builddir/build/BUILD/MellowPlayer-402e336880f94853a541fc3e773e593b584fe8e0/src/3rdparty/boost-di-extensions/Factory.hpp:31:24:
  required from here
BUILDSTDERR:
/builddir/build/BUILD/MellowPlayer-402e336880f94853a541fc3e773e593b584fe8e0/src/3rdparty/boost-di-extensions/Factory.hpp:45:32:
error: redundant move in return statement [-Werror=redundant-move]
BUILDSTDERR:    45 |         return std::move(object);
BUILDSTDERR:       |                                ^

https://stackoverflow.com/questions/9532608/is-returning-with-stdmove-sen...

For local variables, there's no need to |std::move| them in the |return|
statement most of the time^† , since the language actually demands that
this happens automatically:

||