D24466: Use ECMGenerateExportHeader to manage deprecated API better

[Friedrich W. H. Kossebau]

kossebau added a comment.


  In D24466#546952 <https://phabricator.kde.org/D24466#546952>, @dfaure wrote:
  
  > Maybe Qt doesn't have any deprecated signals?
  
  
  That would be nice :) A few there are though, e.g. see here some for QComboBox, only using `QT_DEPRECATED_SINCE` & `QT_DEPRECATED_VERSION_X`, but not `QT_MOC_COMPAT`:
  https://code.woboq.org/qt5/qtbase/src/widgets/widgets/qcombobox.h.html#223
  
  Perhaps people forgot about it, the macro also not being documented anywhere.
  
  Now finally got around to do some test code to check deprecation with signal/slots:
  
    #include <QObject>
    #include <QCoreApplication>
    #include <QDebug>
    
    class Object : public QObject
    {
        Q_OBJECT
    
    public Q_SLOTS:
        Q_DECL_DEPRECATED
        QT_MOC_COMPAT
        void slotIt() {
            qDebug() << "handling signal";
        }
    
    Q_SIGNALS:
        Q_DECL_DEPRECATED
        QT_MOC_COMPAT
        void signalIt();
    };
    
    int main(int argc, char *argv[])
    {
        QCoreApplication app(argc, argv);
    
        Object object;
        QObject::connect(&object, SIGNAL(signalIt()), &object, SLOT(slotIt()));
        QObject::connect(&object, &Object::signalIt, &object, &Object::slotIt);
    
        emit object.signalIt();
    
        return 0;
    }
    
    #include "main.moc"
  
  When building this gives:
  
    main.cpp: In function ‘int main(int, char**)’:
    main.cpp:29:40: warning: ‘void Object::signalIt()’ is deprecated [-Wdeprecated-declarations]
       29 |     QObject::connect(&object, &Object::signalIt, &object, &Object::slotIt);
          |                                        ^~~~~~~~
    main.cpp:20:10: note: declared here
       20 |     void signalIt();
          |          ^~~~~~~~
    main.cpp:29:68: warning: ‘void Object::slotIt()’ is deprecated [-Wdeprecated-declarations]
       29 |     QObject::connect(&object, &Object::signalIt, &object, &Object::slotIt);
          |                                                                    ^~~~~~
    main.cpp:13:10: note: declared here
       13 |     void slotIt() {
          |          ^~~~~~
    main.cpp:31:26: warning: ‘void Object::signalIt()’ is deprecated [-Wdeprecated-declarations]
       31 |     emit object.signalIt();
          |                          ^
    main.cpp:20:10: note: declared here
       20 |     void signalIt();
          |          ^~~~~~~~
  
  and when running just
  
    handling signal
    handling signal
  
  so no runtime warning about the compat signal or slot. Possibly as QT_NO_DEBUG is said to be defined for Qt release builds, so `check_and_warn_compat` will not be run.
  
  So having a _DEPRECATED with signal makes sense also for consumers connecting to the signal with memberfunction-pointer based connect. Will adapt the other patches accordingly.
  
  Not sure what to do about the QT_MOC_COMPAT, so far it should not hurt to keep them, but the question is how useful adding new ones is and whether this is future-proof.

REPOSITORY
  R263 KXmlGui

BRANCH
  deprecatedapi

REVISION DETAIL
  https://phabricator.kde.org/D24466

To: kossebau, #frameworks, dfaure, mlaurent
Cc: kde-frameworks-devel, LeGast00n, GB_2, michaelh, ngraham, bruns
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