Qt6 porting, undefined symbol: _ZN10EngineBase16staticMetaObjectEHi

sebaro

I use a build directory, and I clean it after each code change:

cd build
cmake ..
make

I replaced/removed deprecated and obsolete class members and changed the main and plugin cmake files:

CMakeLists.txt

# ------------------------------------------------------------------------------
#  YAROCK CMAKE FILE
# ------------------------------------------------------------------------------
cmake_minimum_required(VERSION 3.16)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)
set(CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/cmake )

PROJECT( yarock )
set(YAROCK_MAJOR_VERSION 1)
set(YAROCK_MINOR_VERSION 5)
set(YAROCK_PATCH_VERSION 0)
set(YAROCK_VERSION "${YAROCK_MAJOR_VERSION}.${YAROCK_MINOR_VERSION}.${YAROCK_PATCH_VERSION}")

# ------------------------------------------------------------------------------
#  build def
# ------------------------------------------------------------------------------
#ADD_DEFINITIONS( -DTEST_FLAG )
ADD_DEFINITIONS(-Wall -Wextra )

# ------------------------------------------------------------------------------
#  OPTION
# ------------------------------------------------------------------------------
# Since yarock 1.1.5 change default audio engine to VLC
OPTION(ENABLE_PHONON "Enable/disable Phonon audio engine" OFF)
OPTION(ENABLE_VLC "Enable/disable VLC audio engine" OFF)
OPTION(ENABLE_MPV "Enable/disable MPV audio engine" ON)
# OPTION(ENABLE_QTMULTIMEDIA "Enable/disable QtMultimedia audio engine" OFF)
OPTION(ENABLE_SHORTCUT "Enable/disable global shortcut manager" OFF)

# ------------------------------------------------------------------------------
#  EXTERNAL PACKAGE
# ------------------------------------------------------------------------------

#---- Qt ----
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${Qt6Widgets_EXECUTABLE_COMPILE_FLAGS}")
find_package(Qt6Gui REQUIRED)
find_package(Qt6Widgets REQUIRED)
find_package(Qt6Xml REQUIRED)
find_package(Qt6Network REQUIRED)
find_package(Qt6Concurrent REQUIRED)
find_package(Qt6DBus REQUIRED)
find_package(Qt6Sql REQUIRED)
find_package(Qt6LinguistTools REQUIRED)
set (QTLIBS ${Qt6Core_LIBRARIES}
            ${Qt6Gui_LIBRARIES}
            ${Qt6Widgets_LIBRARIES}
            ${Qt6Network_LIBRARIES}
            ${Qt6Xml_LIBRARIES}
            ${Qt6Concurrent_LIBRARIES}
            ${Qt6DBus_LIBRARIES}
            ${Qt6Sql_LIBRARIES})
set (QTINCLUDES ${Qt6Core_INCLUDE_DIRS}
                ${Qt6Gui_INCLUDE_DIRS}
                ${Qt6Widgets_INCLUDE_DIRS}
                ${Qt6Network_INCLUDE_DIRS}
                ${Qt6Xml_INCLUDE_DIRS}
                ${Qt6Concurrent_INCLUDE_DIRS}
                ${Qt6DBus_INCLUDE_DIRS}
                ${Qt6Sql_INCLUDE_DIRS})
add_definitions( ${Qt6Core_DEFINITIONS}
                 ${Qt6Widgets_DEFINITIONS}
                 ${Qt6Network_DEFINITIONS}
                 ${Qt6Xml_DEFINITIONS}
                 ${Qt6Concurrent_DEFINITIONS})
qt_standard_project_setup()

# ---- Taglib ----
find_package( Taglib 1.6.0 REQUIRED )
if(TAGLIB_FOUND)
    include(CheckTagLibFileName)
    check_taglib_filename(COMPLEX_TAGLIB_FILENAME)
endif (TAGLIB_FOUND)

# ---- Htmlcxx ----
find_package( HtmlCxx )

# ------------------------------------------------------------------------------
#  INCLUDES
# ------------------------------------------------------------------------------
INCLUDE_DIRECTORIES( ${QTINCLUDES} )
INCLUDE_DIRECTORIES( ${TAGLIB_INCLUDES} )
INCLUDE_DIRECTORIES( ${HTMLCXX_INCLUDE_DIRS} )

# ------------------------------------------------------------------------------
#  SUBDIRECTORIES
# ------------------------------------------------------------------------------
# global shortcut
if(ENABLE_SHORTCUT)
  add_definitions(-DENABLE_SHORTCUT)

  add_subdirectory(src/shortcuts)

  INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR}/src/shortcuts)

  set(LIB_INTERNAL_STATIC_SHORTCUT yarock_shortchut)

endif(ENABLE_SHORTCUT)

# ------------------------------------------------------------------------------
#  INSTALL DIRECTORIES
# ------------------------------------------------------------------------------
if (CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
   set (CMAKE_INSTALL_PREFIX /usr CACHE PATH "default install path" FORCE )
endif()

set(CMAKE_INSTALL_BIN          "${CMAKE_INSTALL_PREFIX}/bin"         CACHE PATH "binaries install path" FORCE)
set(CMAKE_INSTALL_LIB          "${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX}/yarock"  CACHE PATH "libraries install path" FORCE)
set(CMAKE_INSTALL_TRANS        "${CMAKE_INSTALL_PREFIX}/share/yarock/translations"  CACHE PATH "translations install path" FORCE)

# ------------------------------------------------------------------------------
#  CONFIGURE FILES
# ------------------------------------------------------------------------------
configure_file(${CMAKE_CURRENT_SOURCE_DIR}/src/config.h.in
               ${CMAKE_CURRENT_BINARY_DIR}/config.h)

# ------------------------------------------------------------------------------
#  SOURCES
# ------------------------------------------------------------------------------
add_subdirectory(src)

MESSAGE(STATUS "Audio Engine Vlc.................................................  " ${ENABLE_VLC} " [use cmake .. -DENABLE_VLC=ON/OFF]" )
if (ENABLE_VLC)
  add_definitions(-DENABLE_VLC)
  add_subdirectory(src/core/player/vlc)
endif (ENABLE_VLC)

MESSAGE(STATUS "Audio Engine Mpv.................................................  " ${ENABLE_MPV} " [use cmake .. -DENABLE_MPV=ON/OFF]")
if (ENABLE_MPV)
  add_definitions(-DENABLE_MPV)
  add_subdirectory(src/core/player/mpv)
endif (ENABLE_MPV)

MESSAGE(STATUS "Audio Engine Phonon..............................................  " ${ENABLE_PHONON} " [use cmake .. -DENABLE_PHONON=ON/OFF]")
if (ENABLE_PHONON)
  add_definitions(-DENABLE_PHONON)
  add_subdirectory(src/core/player/phonon)
endif (ENABLE_PHONON)

# MESSAGE(STATUS "Audio Engine QtMultimedia........................................  " ${ENABLE_QTMULTIMEDIA} " [use cmake .. -DENABLE_QTMULTIMEDIA=ON/OFF]")
# if (ENABLE_QTMULTIMEDIA)
#     if (ENABLE_QT5)
#       add_definitions(-DENABLE_QTMULTIMEDIA)
#       add_subdirectory(src/core/player/qtmultimedia)
#     else (ENABLE_QT5)
#       MESSAGE(WARNING "QtMultimedia can be set with QT5")
#     endif (ENABLE_QT5)
# endif (ENABLE_QTMULTIMEDIA)

INCLUDE_DIRECTORIES(${CMAKE_SOURCE_DIR})
INCLUDE_DIRECTORIES(${CMAKE_CURRENT_SOURCE_DIR})
INCLUDE_DIRECTORIES(${CMAKE_BINARY_DIR})
INCLUDE_DIRECTORIES(${YAROCK_INCLUDES})

# ------------------------------------------------------------------------------
#  RESSOURCE
# ------------------------------------------------------------------------------
SET(YAROCK_RESOURCES yarock.qrc)

QT6_ADD_RESOURCES(YAROCK_RESOURCES_RCC ${YAROCK_RESOURCES})

# ------------------------------------------------------------------------------
#  DBUS
# ------------------------------------------------------------------------------
# MPRIS 2.0 DBUS interfaces
qt6_add_dbus_adaptor(YAROCK_SOURCES
     src/dbus/org.mpris.MediaPlayer2.Player.xml
     src/dbus/mpris2.h Mpris2 mpris2Player Mpris2Player)
qt6_add_dbus_adaptor(YAROCK_SOURCES
     src/dbus/org.mpris.MediaPlayer2.xml
     src/dbus/mpris2.h Mpris2 mpris2Root Mpris2Root)

# ------------------------------------------------------------------------------
#  TRANSLATION
# ------------------------------------------------------------------------------
# Handle Translations, take all * files from trans directory.
file( GLOB TRANS_FILES ${CMAKE_SOURCE_DIR}/translation/yarock_*.ts)
set(TS_FILES ${TRANS_FILES})

SET(UPDATE_TRANSLATIONS OFF) # no ts update
#SET(UPDATE_TRANSLATIONS ON) # ts update

option (UPDATE_TRANSLATIONS "Update source translation ../translation/*.ts files")
set (FILES_TO_TRANSLATE ${FILES_TO_TRANSLATE} ${YAROCK_SOURCES})

if (UPDATE_TRANSLATIONS)
  QT6_CREATE_TRANSLATION(YAROCK_QM_FILES ${FILES_TO_TRANSLATE} ${TS_FILES})
else (UPDATE_TRANSLATIONS)
  QT6_ADD_TRANSLATION(YAROCK_QM_FILES ${TS_FILES})
endif (UPDATE_TRANSLATIONS)

# ------------------------------------------------------------------------------
#  BUILDING
# ------------------------------------------------------------------------------
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Wall")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Woverloaded-virtual -Wall -Wno-sign-compare")

ADD_EXECUTABLE(yarock ${YAROCK_SOURCES} ${YAROCK_RESOURCES_RCC} ${YAROCK_QM_FILES})

SET_TARGET_PROPERTIES(yarock PROPERTIES AUTOMOC TRUE)

SET_PROPERTY(TARGET  ${LIB_INTERNAL_STATIC_SHORTCUT} PROPERTY IMPORTED_LOCATION ${CMAKE_SOURCE_DIR}/shortcuts)

if(ENABLE_SHORTCUT)
  TARGET_LINK_LIBRARIES(yarock ${LIB_INTERNAL_STATIC_SHORTCUT})
endif(ENABLE_SHORTCUT)

TARGET_LINK_LIBRARIES(yarock
  X11
  ${QTLIBS}
  ${TAGLIB_LIBRARIES}
  ${HTMLCXX_LIBRARIES}
)

# ------------------------------------------------------------------------------
#  INSTALL
# ------------------------------------------------------------------------------
# -- install binary file
install( TARGETS yarock DESTINATION ${CMAKE_INSTALL_BIN} )

# -- install translations files
install(FILES ${YAROCK_QM_FILES} DESTINATION "${CMAKE_INSTALL_PREFIX}/share/yarock/translations")

# -- install destop file
install(FILES data/org.yarock.desktop  DESTINATION "${CMAKE_INSTALL_PREFIX}/share/applications" )

# -- install appdata file
install(FILES data/org.yarock.appdata.xml  DESTINATION "${CMAKE_INSTALL_PREFIX}/share/appdata" )

# -- install icons files
INSTALL( FILES ${CMAKE_SOURCE_DIR}/icon/yarock_16x16.png DESTINATION "${CMAKE_INSTALL_PREFIX}/share/icons/hicolor/16x16/apps" RENAME application-x-yarock.png)
INSTALL( FILES ${CMAKE_SOURCE_DIR}/icon/yarock_32x32.png DESTINATION "${CMAKE_INSTALL_PREFIX}/share/icons/hicolor/32x32/apps" RENAME application-x-yarock.png)
INSTALL( FILES ${CMAKE_SOURCE_DIR}/icon/yarock_48x48.png DESTINATION "${CMAKE_INSTALL_PREFIX}/share/icons/hicolor/48x48/apps" RENAME application-x-yarock.png)
INSTALL( FILES ${CMAKE_SOURCE_DIR}/icon/yarock_64x64.png DESTINATION "${CMAKE_INSTALL_PREFIX}/share/icons/hicolor/64x64/apps" RENAME application-x-yarock.png)
INSTALL( FILES ${CMAKE_SOURCE_DIR}/icon/yarock_128x128.png DESTINATION "${CMAKE_INSTALL_PREFIX}/share/icons/hicolor/128x128/apps" RENAME application-x-yarock.png)
INSTALL( FILES ${CMAKE_SOURCE_DIR}/icon/yarock.svg DESTINATION "${CMAKE_INSTALL_PREFIX}/share/icons/hicolor/scalable/apps" RENAME application-x-yarock.svg)
INSTALL( FILES ${CMAKE_SOURCE_DIR}/icon/yarock_48x48.png DESTINATION "${CMAKE_INSTALL_PREFIX}/share/pixmaps/" RENAME application-x-yarock.png)

# ------------------------------------------------------------------------------
#  UN-INSTALL SUPPORT
# ------------------------------------------------------------------------------

src/core/player/mpv/CMakeLists.txt

# ------------------------------------------------------------------------------
#  MPV PLUGIN CMAKE FILE
# ------------------------------------------------------------------------------
cmake_minimum_required(VERSION 3.16)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

project(enginempv)
# ------------------------------------------------------------------------------
#  build def (QT PLUGIN)
# ------------------------------------------------------------------------------
ADD_DEFINITIONS( -Wall )
ADD_DEFINITIONS(-DQT_PLUGIN)
ADD_DEFINITIONS(-DQT_NO_DEBUG)
ADD_DEFINITIONS(-DQT_SHARED)
ADD_DEFINITIONS(-DQT_THREAD)


ADD_DEFINITIONS( -DENABLE_MPV )

# ------------------------------------------------------------------------------
#  EXTERNAL LIB
# ------------------------------------------------------------------------------
FIND_PACKAGE( LIBMPV REQUIRED)


# ------------------------------------------------------------------------------
#  INCLUDES
# ------------------------------------------------------------------------------
INCLUDE_DIRECTORIES( ${CMAKE_CURRENT_SOURCE_DIR}/../../../../src/core/player/
                     ${CMAKE_CURRENT_SOURCE_DIR}/../../../../src/core/player/mpv
                     ${CMAKE_CURRENT_SOURCE_DIR}/../../../../src/core/mediaitem
                     ${CMAKE_CURRENT_SOURCE_DIR}/../../../../src
)

INCLUDE_DIRECTORIES( ${LIBMPV_INCLUDE_DIR} )

set (QTLIBS ${Qt6Core_LIBRARIES})
set (QTINCLUDES ${Qt6Core_INCLUDE_DIRS})
add_definitions( ${Qt6Core_DEFINITIONS})
qt_standard_project_setup()

INCLUDE_DIRECTORIES( ${QTINCLUDES} )

# ------------------------------------------------------------------------------
#  SOURCES
# ------------------------------------------------------------------------------
SET(SOURCES
    ${CMAKE_CURRENT_SOURCE_DIR}/../../../../src/core/player/mpv/engine_mpv.cpp
)

# ------------------------------------------------------------------------------
#  BUILDING
# ------------------------------------------------------------------------------
set( CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib )

ADD_LIBRARY( enginempv SHARED ${SOURCES} )

SET_TARGET_PROPERTIES(enginempv PROPERTIES AUTOMOC TRUE)

ADD_DEPENDENCIES(enginempv yarock)

TARGET_LINK_LIBRARIES(enginempv ${LIBMPV_LIBRARY} ${QTLIBS})

# ------------------------------------------------------------------------------
#  INSTALL
# ------------------------------------------------------------------------------
if (CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
   set (CMAKE_INSTALL_PREFIX /usr CACHE PATH "default install path" FORCE )
endif()

set(CMAKE_INSTALL_LIB "${CMAKE_INSTALL_PREFIX}/lib${LIB_SUFFIX}/yarock"  CACHE PATH "libraries installation path" FORCE)

install(TARGETS enginempv DESTINATION ${CMAKE_INSTALL_LIB} )

I still think has something to do with the c++-17 standard, if I add these in the old code (qt5) I get the same undefined symbol:

set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

Thanks

JonB

@sebaro said in Qt6 porting, undefined symbol: _ZN10EngineBase16staticMetaObjectEHi:

I clean it after each code change

And precisely what does that mean? I suggested you delete the build output directory. If something like make clean that may not be good enough. Just saying, up to you.

sebaro

@JonB

I delete the content of build directory, I don't use make clean. Every cmake/make is with an empty build directory.

JonB

@sebaro Fair enough.

Christian Ehrlicher

Simplify your testcase until you find the bug or you can post it here.

sierdzio

@sebaro you are not running moc anywhere, so meta object information is not generated.

In your cmake files, add this:

set(CMAKE_AUTOMOC ON)

sebaro

Automoc was set to true, added CMAKE_AUTOMOC:

set(CMAKE_AUTOMOC ON)
qt_standard_project_setup()
SET_TARGET_PROPERTIES(enginempv PROPERTIES AUTOMOC TRUE)

It's in the build progress "Automatic MOC and UIC":

[ 98%] Built target enginempv_autogen_timestamp_deps
[ 98%] Automatic MOC and UIC for target enginempv
[ 98%] Built target enginempv_autogen
[ 99%] Building CXX object src/core/player/mpv/CMakeFiles/enginempv.dir/engine_mpv.cpp.o
[ 99%] Building CXX object src/core/player/mpv/CMakeFiles/enginempv.dir/enginempv_autogen/mocs_compilation.cpp.o
[100%] Linking CXX shared library ../../../../lib/libenginempv.so
[100%] Built target enginempv

c++filt _ZN10EngineBase16staticMetaObjectE
EngineBase::staticMetaObject

I see the moc files are generated and they contain EngineBase::staticMetaObject:

moc_engine_base.cpp

/****************************************************************************
** Meta object code from reading C++ file 'engine_base.h'
**
** Created by: The Qt Meta Object Compiler version 68 (Qt 6.7.0)
**
** WARNING! All changes made in this file will be lost!
*****************************************************************************/

#include "../../../src/core/player/engine_base.h"
#include <QtCore/qmetatype.h>

#include <QtCore/qtmochelpers.h>

#include <memory>


#include <QtCore/qxptype_traits.h>
#if !defined(Q_MOC_OUTPUT_REVISION)
#error "The header file 'engine_base.h' doesn't include <QObject>."
#elif Q_MOC_OUTPUT_REVISION != 68
#error "This file was generated using the moc from 6.7.0. It"
#error "cannot be used with the include files from this version of Qt."
#error "(The moc has changed too much.)"
#endif

#ifndef Q_CONSTINIT
#define Q_CONSTINIT
#endif

QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
QT_WARNING_DISABLE_GCC("-Wuseless-cast")
namespace {

#ifdef QT_MOC_HAS_STRINGDATA
struct qt_meta_stringdata_CLASSEngineBaseENDCLASS_t {};
constexpr auto qt_meta_stringdata_CLASSEngineBaseENDCLASS = QtMocHelpers::stringData(
    "EngineBase",
    "mediaChanged",
    "",
    "mediaMetaDataChanged",
    "mediaAboutToFinish",
    "mediaFinished",
    "mediaTick",
    "time",
    "mediaTotalTimeChanged",
    "newTotalTime",
    "mediaSeekableChanged",
    "engineQueueFinished",
    "engineStateChanged",
    "engineRequestStop",
    "volumeChanged",
    "muteStateChanged",
    "volumeMute",
    "volumeInc",
    "volumeDec"
);
#else  // !QT_MOC_HAS_STRINGDATA
#error "qtmochelpers.h not found or too old."
#endif // !QT_MOC_HAS_STRINGDATA
} // unnamed namespace

Q_CONSTINIT static const uint qt_meta_data_CLASSEngineBaseENDCLASS[] = {

 // content:
      12,       // revision
       0,       // classname
       0,    0, // classinfo
      15,   14, // methods
       0,    0, // properties
       0,    0, // enums/sets
       0,    0, // constructors
       0,       // flags
      12,       // signalCount

 // signals: name, argc, parameters, tag, flags, initial metatype offsets
       1,    0,  104,    2, 0x06,    1 /* Public */,
       3,    0,  105,    2, 0x06,    2 /* Public */,
       4,    0,  106,    2, 0x06,    3 /* Public */,
       5,    0,  107,    2, 0x06,    4 /* Public */,
       6,    1,  108,    2, 0x06,    5 /* Public */,
       8,    1,  111,    2, 0x06,    7 /* Public */,
      10,    1,  114,    2, 0x06,    9 /* Public */,
      11,    0,  117,    2, 0x06,   11 /* Public */,
      12,    0,  118,    2, 0x06,   12 /* Public */,
      13,    0,  119,    2, 0x06,   13 /* Public */,
      14,    0,  120,    2, 0x06,   14 /* Public */,
      15,    0,  121,    2, 0x06,   15 /* Public */,

 // slots: name, argc, parameters, tag, flags, initial metatype offsets
      16,    0,  122,    2, 0x0a,   16 /* Public */,
      17,    0,  123,    2, 0x0a,   17 /* Public */,
      18,    0,  124,    2, 0x0a,   18 /* Public */,

 // signals: parameters
    QMetaType::Void,
    QMetaType::Void,
    QMetaType::Void,
    QMetaType::Void,
    QMetaType::Void, QMetaType::LongLong,    7,
    QMetaType::Void, QMetaType::LongLong,    9,
    QMetaType::Void, QMetaType::Bool,    2,
    QMetaType::Void,
    QMetaType::Void,
    QMetaType::Void,
    QMetaType::Void,
    QMetaType::Void,

 // slots: parameters
    QMetaType::Void,
    QMetaType::Void,
    QMetaType::Void,

       0        // eod
};

Q_CONSTINIT const QMetaObject EngineBase::staticMetaObject = { {
    QMetaObject::SuperData::link<QObject::staticMetaObject>(),
    qt_meta_stringdata_CLASSEngineBaseENDCLASS.offsetsAndSizes,
    qt_meta_data_CLASSEngineBaseENDCLASS,
    qt_static_metacall,
    nullptr,
    qt_incomplete_metaTypeArray<qt_meta_stringdata_CLASSEngineBaseENDCLASS_t,
        // Q_OBJECT / Q_GADGET
        QtPrivate::TypeAndForceComplete<EngineBase, std::true_type>,
        // method 'mediaChanged'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'mediaMetaDataChanged'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'mediaAboutToFinish'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'mediaFinished'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'mediaTick'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        QtPrivate::TypeAndForceComplete<qint64, std::false_type>,
        // method 'mediaTotalTimeChanged'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        QtPrivate::TypeAndForceComplete<qint64, std::false_type>,
        // method 'mediaSeekableChanged'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        QtPrivate::TypeAndForceComplete<bool, std::false_type>,
        // method 'engineQueueFinished'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'engineStateChanged'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'engineRequestStop'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'volumeChanged'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'muteStateChanged'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'volumeMute'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'volumeInc'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'volumeDec'
        QtPrivate::TypeAndForceComplete<void, std::false_type>
    >,
    nullptr
} };

void EngineBase::qt_static_metacall(QObject *_o, QMetaObject::Call _c, int _id, void **_a)
{
    if (_c == QMetaObject::InvokeMetaMethod) {
        auto *_t = static_cast<EngineBase *>(_o);
        (void)_t;
        switch (_id) {
        case 0: _t->mediaChanged(); break;
        case 1: _t->mediaMetaDataChanged(); break;
        case 2: _t->mediaAboutToFinish(); break;
        case 3: _t->mediaFinished(); break;
        case 4: _t->mediaTick((*reinterpret_cast< std::add_pointer_t<qint64>>(_a[1]))); break;
        case 5: _t->mediaTotalTimeChanged((*reinterpret_cast< std::add_pointer_t<qint64>>(_a[1]))); break;
        case 6: _t->mediaSeekableChanged((*reinterpret_cast< std::add_pointer_t<bool>>(_a[1]))); break;
        case 7: _t->engineQueueFinished(); break;
        case 8: _t->engineStateChanged(); break;
        case 9: _t->engineRequestStop(); break;
        case 10: _t->volumeChanged(); break;
        case 11: _t->muteStateChanged(); break;
        case 12: _t->volumeMute(); break;
        case 13: _t->volumeInc(); break;
        case 14: _t->volumeDec(); break;
        default: ;
        }
    } else if (_c == QMetaObject::IndexOfMethod) {
        int *result = reinterpret_cast<int *>(_a[0]);
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::mediaChanged; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 0;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::mediaMetaDataChanged; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 1;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::mediaAboutToFinish; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 2;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::mediaFinished; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 3;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)(qint64 );
            if (_t _q_method = &EngineBase::mediaTick; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 4;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)(qint64 );
            if (_t _q_method = &EngineBase::mediaTotalTimeChanged; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 5;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)(bool );
            if (_t _q_method = &EngineBase::mediaSeekableChanged; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 6;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::engineQueueFinished; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 7;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::engineStateChanged; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 8;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::engineRequestStop; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 9;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::volumeChanged; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 10;
                return;
            }
        }
        {
            using _t = void (EngineBase::*)();
            if (_t _q_method = &EngineBase::muteStateChanged; *reinterpret_cast<_t *>(_a[1]) == _q_method) {
                *result = 11;
                return;
            }
        }
    }
}

const QMetaObject *EngineBase::metaObject() const
{
    return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
}

void *EngineBase::qt_metacast(const char *_clname)
{
    if (!_clname) return nullptr;
    if (!strcmp(_clname, qt_meta_stringdata_CLASSEngineBaseENDCLASS.stringdata0))
        return static_cast<void*>(this);
    return QObject::qt_metacast(_clname);
}

int EngineBase::qt_metacall(QMetaObject::Call _c, int _id, void **_a)
{
    _id = QObject::qt_metacall(_c, _id, _a);
    if (_id < 0)
        return _id;
    if (_c == QMetaObject::InvokeMetaMethod) {
        if (_id < 15)
            qt_static_metacall(this, _c, _id, _a);
        _id -= 15;
    } else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
        if (_id < 15)
            *reinterpret_cast<QMetaType *>(_a[0]) = QMetaType();
        _id -= 15;
    }
    return _id;
}

// SIGNAL 0
void EngineBase::mediaChanged()
{
    QMetaObject::activate(this, &staticMetaObject, 0, nullptr);
}

// SIGNAL 1
void EngineBase::mediaMetaDataChanged()
{
    QMetaObject::activate(this, &staticMetaObject, 1, nullptr);
}

// SIGNAL 2
void EngineBase::mediaAboutToFinish()
{
    QMetaObject::activate(this, &staticMetaObject, 2, nullptr);
}

// SIGNAL 3
void EngineBase::mediaFinished()
{
    QMetaObject::activate(this, &staticMetaObject, 3, nullptr);
}

// SIGNAL 4
void EngineBase::mediaTick(qint64 _t1)
{
    void *_a[] = { nullptr, const_cast<void*>(reinterpret_cast<const void*>(std::addressof(_t1))) };
    QMetaObject::activate(this, &staticMetaObject, 4, _a);
}

// SIGNAL 5
void EngineBase::mediaTotalTimeChanged(qint64 _t1)
{
    void *_a[] = { nullptr, const_cast<void*>(reinterpret_cast<const void*>(std::addressof(_t1))) };
    QMetaObject::activate(this, &staticMetaObject, 5, _a);
}

// SIGNAL 6
void EngineBase::mediaSeekableChanged(bool _t1)
{
    void *_a[] = { nullptr, const_cast<void*>(reinterpret_cast<const void*>(std::addressof(_t1))) };
    QMetaObject::activate(this, &staticMetaObject, 6, _a);
}

// SIGNAL 7
void EngineBase::engineQueueFinished()
{
    QMetaObject::activate(this, &staticMetaObject, 7, nullptr);
}

// SIGNAL 8
void EngineBase::engineStateChanged()
{
    QMetaObject::activate(this, &staticMetaObject, 8, nullptr);
}

// SIGNAL 9
void EngineBase::engineRequestStop()
{
    QMetaObject::activate(this, &staticMetaObject, 9, nullptr);
}

// SIGNAL 10
void EngineBase::volumeChanged()
{
    QMetaObject::activate(this, &staticMetaObject, 10, nullptr);
}

// SIGNAL 11
void EngineBase::muteStateChanged()
{
    QMetaObject::activate(this, &staticMetaObject, 11, nullptr);
}
QT_WARNING_POP

moc_engine_mpv.cpp

/****************************************************************************
** Meta object code from reading C++ file 'engine_mpv.h'
**
** Created by: The Qt Meta Object Compiler version 68 (Qt 6.7.0)
**
** WARNING! All changes made in this file will be lost!
*****************************************************************************/

#include "../../../../../../../src/core/player/mpv/engine_mpv.h"
#include <QtCore/qmetatype.h>
#include <QtCore/qplugin.h>

#include <QtCore/qtmochelpers.h>

#include <memory>


#include <QtCore/qxptype_traits.h>
#if !defined(Q_MOC_OUTPUT_REVISION)
#error "The header file 'engine_mpv.h' doesn't include <QObject>."
#elif Q_MOC_OUTPUT_REVISION != 68
#error "This file was generated using the moc from 6.7.0. It"
#error "cannot be used with the include files from this version of Qt."
#error "(The moc has changed too much.)"
#endif

#ifndef Q_CONSTINIT
#define Q_CONSTINIT
#endif

QT_WARNING_PUSH
QT_WARNING_DISABLE_DEPRECATED
QT_WARNING_DISABLE_GCC("-Wuseless-cast")
namespace {

#ifdef QT_MOC_HAS_STRINGDATA
struct qt_meta_stringdata_CLASSEngineMpvENDCLASS_t {};
constexpr auto qt_meta_stringdata_CLASSEngineMpvENDCLASS = QtMocHelpers::stringData(
    "EngineMpv",
    "volumeMute",
    "",
    "volumeInc",
    "volumeDec"
);
#else  // !QT_MOC_HAS_STRINGDATA
#error "qtmochelpers.h not found or too old."
#endif // !QT_MOC_HAS_STRINGDATA
} // unnamed namespace

Q_CONSTINIT static const uint qt_meta_data_CLASSEngineMpvENDCLASS[] = {

 // content:
      12,       // revision
       0,       // classname
       0,    0, // classinfo
       3,   14, // methods
       0,    0, // properties
       0,    0, // enums/sets
       0,    0, // constructors
       0,       // flags
       0,       // signalCount

 // slots: name, argc, parameters, tag, flags, initial metatype offsets
       1,    0,   32,    2, 0x0a,    1 /* Public */,
       3,    0,   33,    2, 0x0a,    2 /* Public */,
       4,    0,   34,    2, 0x0a,    3 /* Public */,

 // slots: parameters
    QMetaType::Void,
    QMetaType::Void,
    QMetaType::Void,

       0        // eod
};

Q_CONSTINIT const QMetaObject EngineMpv::staticMetaObject = { {
    QMetaObject::SuperData::link<EngineBase::staticMetaObject>(),
    qt_meta_stringdata_CLASSEngineMpvENDCLASS.offsetsAndSizes,
    qt_meta_data_CLASSEngineMpvENDCLASS,
    qt_static_metacall,
    nullptr,
    qt_incomplete_metaTypeArray<qt_meta_stringdata_CLASSEngineMpvENDCLASS_t,
        // Q_OBJECT / Q_GADGET
        QtPrivate::TypeAndForceComplete<EngineMpv, std::true_type>,
        // method 'volumeMute'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'volumeInc'
        QtPrivate::TypeAndForceComplete<void, std::false_type>,
        // method 'volumeDec'
        QtPrivate::TypeAndForceComplete<void, std::false_type>
    >,
    nullptr
} };

void EngineMpv::qt_static_metacall(QObject *_o, QMetaObject::Call _c, int _id, void **_a)
{
    if (_c == QMetaObject::InvokeMetaMethod) {
        auto *_t = static_cast<EngineMpv *>(_o);
        (void)_t;
        switch (_id) {
        case 0: _t->volumeMute(); break;
        case 1: _t->volumeInc(); break;
        case 2: _t->volumeDec(); break;
        default: ;
        }
    }
    (void)_a;
}

const QMetaObject *EngineMpv::metaObject() const
{
    return QObject::d_ptr->metaObject ? QObject::d_ptr->dynamicMetaObject() : &staticMetaObject;
}

void *EngineMpv::qt_metacast(const char *_clname)
{
    if (!_clname) return nullptr;
    if (!strcmp(_clname, qt_meta_stringdata_CLASSEngineMpvENDCLASS.stringdata0))
        return static_cast<void*>(this);
    if (!strcmp(_clname, "yarock.EngineBase/1.0"))
        return static_cast< EngineBase*>(this);
    return EngineBase::qt_metacast(_clname);
}

int EngineMpv::qt_metacall(QMetaObject::Call _c, int _id, void **_a)
{
    _id = EngineBase::qt_metacall(_c, _id, _a);
    if (_id < 0)
        return _id;
    if (_c == QMetaObject::InvokeMetaMethod) {
        if (_id < 3)
            qt_static_metacall(this, _c, _id, _a);
        _id -= 3;
    } else if (_c == QMetaObject::RegisterMethodArgumentMetaType) {
        if (_id < 3)
            *reinterpret_cast<QMetaType *>(_a[0]) = QMetaType();
        _id -= 3;
    }
    return _id;
}

#ifdef QT_MOC_EXPORT_PLUGIN_V2
static constexpr unsigned char qt_pluginMetaDataV2_EngineMpv[] = {
    0xbf, 
    // "IID"
    0x02,  0x69,  'E',  'n',  'g',  'i',  'n',  'e', 
    'M',  'p',  'v', 
    // "className"
    0x03,  0x69,  'E',  'n',  'g',  'i',  'n',  'e', 
    'M',  'p',  'v', 
    0xff, 
};
QT_MOC_EXPORT_PLUGIN_V2(EngineMpv, EngineMpv, qt_pluginMetaDataV2_EngineMpv)
#else
QT_PLUGIN_METADATA_SECTION
Q_CONSTINIT static constexpr unsigned char qt_pluginMetaData_EngineMpv[] = {
    'Q', 'T', 'M', 'E', 'T', 'A', 'D', 'A', 'T', 'A', ' ', '!',
    // metadata version, Qt version, architectural requirements
    0, QT_VERSION_MAJOR, QT_VERSION_MINOR, qPluginArchRequirements(),
    0xbf, 
    // "IID"
    0x02,  0x69,  'E',  'n',  'g',  'i',  'n',  'e', 
    'M',  'p',  'v', 
    // "className"
    0x03,  0x69,  'E',  'n',  'g',  'i',  'n',  'e', 
    'M',  'p',  'v', 
    0xff, 
};
QT_MOC_EXPORT_PLUGIN(EngineMpv, EngineMpv)
#endif  // QT_MOC_EXPORT_PLUGIN_V2

QT_WARNING_POP

sierdzio

@sebaro so, problem solved?

sebaro

@sierdzio
No

sebaro

This post is deleted!

sebaro

Changing to the previous minimum required version of cmake fixes this:

CMakeLists.txt

cmake_minimum_required(VERSION 2.8.6)
#cmake_minimum_required(VERSION 3.16)

src/core/player/mpv/CMakeLists.txt

cmake_minimum_required(VERSION 2.6)
#cmake_minimum_required(VERSION 3.16)

Seems to be this policy:
https://cmake.org/cmake/help/latest/policy/CMP0065.html

This fixed the issue with cmake 3.4+:

set_target_properties(yarock PROPERTIES ENABLE_EXPORTS TRUE)