Auto-generated properties by macros failed due to using an included definition file.

farta

Hello guys, I'm composing a Qt class with many qt properties. So, I want to use macros to reduce repeating work. My code looks like this:

// myservice.h
// the myservice.cpp is trivial, nothing more than an auto-generated constructor.
#ifndef MYSERVICE_H
#define MYSERVICE_H

#include <QObject>

class MyService : public QObject
{
    Q_OBJECT
public:
    explicit MyService(QObject *parent = nullptr);

#define MY_PROPERTY(type, name) \
    Q_PROPERTY(type name MEMBER m_##name NOTIFY name##Changed)
#include "property_list"
#undef MY_PROPERTY

signals:
#define MY_PROPERTY(type, name) \
    void name##Changed(type);
#include "property_list"
#undef MY_PROPERTY

private:
#define MY_PROPERTY(type, name) \
    type m_##name;
#include "property_list"
#undef MY_PROPERTY
};
#endif // MYSERVICE_H

And I'm using a property_list file to define properties, it looks like this:

MY_PROPERTY(QString, value1)
MY_PROPERTY(QString, value2)

But during building, I got these errors:

moc_myservice.cpp: In static member function ‘static void MyService::qt_static_metacall(QObject*, QMetaObject::Call, int, void**)’:
moc_myservice.cpp:92:41: error: no matching function for call to ‘MyService::value1Changed()’
   92 |                 Q_EMIT _t->value1Changed();
      |                        ~~~~~~~~~~~~~~~~~^~
In file included from moc_myservice.cpp:10:
../qt01/property_list:1:22: note: candidate: ‘void MyService::value1Changed(QString)’
    1 | MY_PROPERTY(QString, value1)
      |                      ^~~~~~
../qt01/myservice.h:19:10: note: in definition of macro ‘MY_PROPERTY’
   19 |     void name##Changed(type);
      |          ^~~~
../qt01/property_list:1:22: note:   candidate expects 1 argument, 0 provided
    1 | MY_PROPERTY(QString, value1)
      |                      ^~~~~~
../qt01/myservice.h:19:10: note: in definition of macro ‘MY_PROPERTY’
   19 |     void name##Changed(type);
      |          ^~~~
moc_myservice.cpp:98:41: error: no matching function for call to ‘MyService::value2Changed()’
   98 |                 Q_EMIT _t->value2Changed();
      |                        ~~~~~~~~~~~~~~~~~^~
../qt01/property_list:2:22: note: candidate: ‘void MyService::value2Changed(QString)’
    2 | MY_PROPERTY(QString, value2)
      |                      ^~~~~~
../qt01/myservice.h:19:10: note: in definition of macro ‘MY_PROPERTY’
   19 |     void name##Changed(type);
      |          ^~~~
../qt01/property_list:2:22: note:   candidate expects 1 argument, 0 provided
    2 | MY_PROPERTY(QString, value2)
      |                      ^~~~~~
../qt01/myservice.h:19:10: note: in definition of macro ‘MY_PROPERTY’
   19 |     void name##Changed(type);
      |          ^~~~
moc_myservice.cpp: In function ‘void checkNotifySignalValidity_MyService(MyService*)’:
moc_myservice.cpp:164:21: error: no matching function for call to ‘MyService::value1Changed()’
  164 |     t->value1Changed();
      |     ~~~~~~~~~~~~~~~~^~
../qt01/property_list:1:22: note: candidate: ‘void MyService::value1Changed(QString)’
    1 | MY_PROPERTY(QString, value1)
      |                      ^~~~~~
../qt01/myservice.h:19:10: note: in definition of macro ‘MY_PROPERTY’
   19 |     void name##Changed(type);
      |          ^~~~
../qt01/property_list:1:22: note:   candidate expects 1 argument, 0 provided
    1 | MY_PROPERTY(QString, value1)
      |                      ^~~~~~
../qt01/myservice.h:19:10: note: in definition of macro ‘MY_PROPERTY’
   19 |     void name##Changed(type);
      |          ^~~~
moc_myservice.cpp:165:21: error: no matching function for call to ‘MyService::value2Changed()’
  165 |     t->value2Changed();
      |     ~~~~~~~~~~~~~~~~^~
../qt01/property_list:2:22: note: candidate: ‘void MyService::value2Changed(QString)’
    2 | MY_PROPERTY(QString, value2)
      |                      ^~~~~~
../qt01/myservice.h:19:10: note: in definition of macro ‘MY_PROPERTY’
   19 |     void name##Changed(type);
      |          ^~~~
../qt01/property_list:2:22: note:   candidate expects 1 argument, 0 provided
    2 | MY_PROPERTY(QString, value2)
      |                      ^~~~~~
../qt01/myservice.h:19:10: note: in definition of macro ‘MY_PROPERTY’
   19 |     void name##Changed(type);
      |          ^~~~

It looks like Qt doesn't generate correct signal definitions. And I found that if I don't use a #include directive on signal macros, but paste property_list file's content like this:

signals:
#define MY_PROPERTY(type, name) \
    void name##Changed(type);
MY_PROPERTY(QString, value1)
MY_PROPERTY(QString, value2)
#undef MY_PROPERTY

All errors will then disappear.
I've tried both Windows & Linux. Windows's compiler version is gcc 7.3 and linux's version is gcc 12.2. They both do the same thing.
So here is the problem:

Why a #include directive differs to pasting the content of the included file here?
Is there a way to resolve this problem except pasting the file's content?

Thanks a lot for any help.

Christian Ehrlicher

It's not a compiler problem but the moc parser. This can only be fixed when someone enhance moc but I guess the usecase is to rare that someone is willing to do it.

farta

@Christian-Ehrlicher Thanks a lot. I got this problem on qt5. I'll try qt6 and if it has the same problem I'll try to file a bug to make it known to qt dev team at least.

Christian Ehrlicher

@farta it will not work with Qt6 either. You can create a bug report but this limitation is already known. There were attempts to use llvm for the parser but it was to slow.

farta

@Christian-Ehrlicher lol if it is a known issue maybe it is not a good idea to report it again. Do you have the bug link at hand right now?

Christian Ehrlicher

@farta you can create a bug report - should not hurt.
Search for 'moc' and 'llvm' - maybe there is a task for it.

farta

@Christian-Ehrlicher OK my bug posted.

https://bugreports.qt.io/browse/QTBUG-116012

Hope for the dev team it means sth.

Christian Ehrlicher

You should attach a minimal, compilable example to the bug report.

farta

@Christian-Ehrlicher Thank you for your advice. The sample code has been added to the bug report.