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

[Martin Gansser]

Hi,

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

[2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87300

How can this be solved ?

Regards Martin

[Jakub Jelinek]

On Thu, Feb 07, 2019 at 10:08:26AM -0000, Martin Gansser wrote:
>  Hi,
>  
>  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
>  
>  [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87300
>  
>  How can this be solved ? 
It is a warning (-Wextra enabled only even), if you are using -Werror, you
need to be prepared to deal with warnings.  See info gcc on the rationale
for the warning.

	Jakub

[Jakub Jelinek]

On Thu, Feb 07, 2019 at 11:17:58AM +0100, Jakub Jelinek wrote:
>  On Thu, Feb 07, 2019 at 10:08:26AM -0000, Martin Gansser wrote:
>  > Hi,
>  > 
>  > 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
>  > 
>  > [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87300
>  > 
>  > How can this be solved ?
>  
>  It is a warning (-Wextra enabled only even), if you are using -Werror, you
>  need to be prepared to deal with warnings.  See info gcc on the rationale
>  for the warning. 
And also see http://gcc.gnu.org/PR86981 and http://gcc.gnu.org/PR87029

	Jakub

[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:

||

[Martin Gansser]

Thanks for your reply.

I will pass this information on to the developer of mellowplayer because I can not make
these changes myself.

[Leigh Scott]

>  Thanks for your reply.
>  
>  I will pass this information on to the developer of mellowplayer because I can not make
>  these changes myself. 
Maybe suppress the error warnings for now

https://paste.fedoraproject.org/paste/0UcXKIQa-Nsqha~eV1scKA/raw

[Martin Gansser]

Works for me, many thanks.

[Jonathan Wakely]

On 07/02/19 11:26 +0100, J. Scheurich wrote:
> 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 
This is not a false positive. Just because GCC *sometimes* gives false
positives for this warning, doesn't mean your case is a false
positive.

Your package SHOULD NOT use -Werror, so if you don't know enough C++
to change the package source code then you should fix the spec file to
remove -Werror from the build flags.


> >[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 
Those are Clang warnings. Using -Wno-blahblah is ignored by GCC if it
doesn't have a -Wblahblah option, *unless* other errors occur, then it
will complain.

So if the code compiles, unknown -Wno-blahblah options are ignored. So
if the -Wredundant-move warning was fixed, GCC would ignore the
-Wno-c++1z-extensions and -Wno-unused-private-field options.

>...
>
>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-sensible-in-the-case-of-multiple-return-statements
>
>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:
>
>||
>
>
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[Martin Gansser]

The developer has already fixed the warnings in the new version 3.5.2.