A lot of Warnings ONLY on MingW compiler

[fem_dev]

I'm developing a cross-platform Qt C++ project.
I compile it in different systems and compilers without any warning or error.
The only system that gives me a different output is:

• Windows 10 x64 using MingW 8.1 (that comes with Qt 5.15.1 installer)

In this specific setup I got 10.100 warnings.
Most of them are repeated, but I will paste here some examples:

C:\Qt\5.15.1\mingw81_64\include\QtCore\qobjectdefs.h:114: warning: optimization attribute on 'constexpr const QMetaObject* qt_getEnumMetaObject(QMessageBox::Icon)' follows definition but the attribute doesn't match [-Wattributes]
In file included from C:\Qt\5.15.1\mingw81_64\include/QtGui/qwindowdefs.h:44,
                 from C:\Qt\5.15.1\mingw81_64\include/QtWidgets/qwidget.h:44,
                 from C:\Qt\5.15.1\mingw81_64\include\QtWidgets/qmainwindow.h:44,
                 from C:\Qt\5.15.1\mingw81_64\include\QtWidgets/QMainWindow:1,
                 from ..\..\rotortest\App\app.h:4,
                 from ..\..\rotortest\App\main.cpp:1:
C:\Qt\5.15.1\mingw81_64\include/QtCore/qobjectdefs.h:114:75: warning: optimization attribute on 'constexpr const QMetaObject* qt_getEnumMetaObject(QMessageBox::Icon)' follows definition but the attribute doesn't match [-Wattributes]
     friend Q_DECL_CONSTEXPR const QMetaObject *qt_getEnumMetaObject(ENUM) noexcept { return &staticMetaObject; } \
                                                                           ^~~~~~~~
C:\Qt\5.15.1\mingw81_64\include/QtCore/qobjectdefs.h:116:30: note: in expansion of macro 'Q_ENUM_IMPL'
 #define Q_ENUM(x) Q_ENUMS(x) Q_ENUM_IMPL(x)
                              ^~~~~~~~~~~
C:\Qt\5.15.1\mingw81_64\include\QtWidgets/qmessagebox.h:79:5: note: in expansion of macro 'Q_ENUM'
     Q_ENUM(Icon)
     ^~~~~~
C:\Qt\5.15.1\mingw81_64\include/QtCore/qobjectdefs.h:114:48: note: previous definition of 'constexpr const QMetaObject* qt_getEnumMetaObject(QCborValue::Type)' was here
     friend Q_DECL_CONSTEXPR const QMetaObject *qt_getEnumMetaObject(ENUM) noexcept { return &staticMetaObject; } \
                                                ^~~~~~~~~~~~~~~~~~~~
C:\Qt\5.15.1\mingw81_64\include/QtCore/qobjectdefs.h:116:30: note: in expansion of macro 'Q_ENUM_IMPL'
 #define Q_ENUM(x) Q_ENUMS(x) Q_ENUM_IMPL(x)
                              ^~~~~~~~~~~
C:\Qt\5.15.1\mingw81_64\include/QtCore/qcborvalue.h:135:5: note: in expansion of macro 'Q_ENUM'
     Q_ENUM(Type)
     ^~~~~~

---

C:\Qt\5.15.1\mingw81_64\include\QtCore\qobjectdefs.h:115: warning: optimization attribute on 'constexpr const char* qt_getEnumName(QMessageBox::Icon)' follows definition but the attribute doesn't match [-Wattributes]
C:\Qt\5.15.1\mingw81_64\include/QtCore/qobjectdefs.h:115:62: warning: optimization attribute on 'constexpr const char* qt_getEnumName(QMessageBox::Icon)' follows definition but the attribute doesn't match [-Wattributes]
     friend Q_DECL_CONSTEXPR const char *qt_getEnumName(ENUM) noexcept { return #ENUM; }
                                                              ^~~~~~~~
C:\Qt\5.15.1\mingw81_64\include/QtCore/qobjectdefs.h:116:30: note: in expansion of macro 'Q_ENUM_IMPL'
 #define Q_ENUM(x) Q_ENUMS(x) Q_ENUM_IMPL(x)
                              ^~~~~~~~~~~
C:\Qt\5.15.1\mingw81_64\include\QtWidgets/qmessagebox.h:79:5: note: in expansion of macro 'Q_ENUM'
     Q_ENUM(Icon)
     ^~~~~~
C:\Qt\5.15.1\mingw81_64\include/QtCore/qobjectdefs.h:115:41: note: previous definition of 'constexpr const char* qt_getEnumName(QAbstractItemView::DragDropMode)' was here
     friend Q_DECL_CONSTEXPR const char *qt_getEnumName(ENUM) noexcept { return #ENUM; }
                                         ^~~~~~~~~~~~~~
C:\Qt\5.15.1\mingw81_64\include/QtCore/qobjectdefs.h:116:30: note: in expansion of macro 'Q_ENUM_IMPL'
 #define Q_ENUM(x) Q_ENUMS(x) Q_ENUM_IMPL(x)
                              ^~~~~~~~~~~
C:\Qt\5.15.1\mingw81_64\include/QtWidgets/qabstractitemview.h:185:5: note: in expansion of macro 'Q_ENUM'
     Q_ENUM(DragDropMode)
     ^~~~~~

---

C:\Qt\5.15.1\mingw81_64\include\QtGui\qvector2d.h:106: warning: optimization attribute on 'constexpr const QVector2D operator*(const QVector2D&, const QVector2D&)' follows definition but the attribute doesn't match [-Wattributes]
In file included from C:\Qt\5.15.1\mingw81_64\include/QtGui/qevent.h:56,
                 from C:\Qt\5.15.1\mingw81_64\include/QtGui/qtextlayout.h:49,
                 from C:\Qt\5.15.1\mingw81_64\include/QtGui/qabstracttextdocumentlayout.h:45,
                 from C:\Qt\5.15.1\mingw81_64\include/QtWidgets/qplaintextedit.h:51,
                 from C:\Qt\5.15.1\mingw81_64\include/QtWidgets/QPlainTextEdit:1,
                 from ./ui_app.h:20,
                 from ..\..\rotortest\App\app.cpp:2:
C:\Qt\5.15.1\mingw81_64\include/QtGui/qvector2d.h:106:102: warning: optimization attribute on 'constexpr const QVector2D operator*(const QVector2D&, const QVector2D&)' follows definition but the attribute doesn't match [-Wattributes]
     Q_DECL_CONSTEXPR friend inline const QVector2D operator*(const QVector2D &v1, const QVector2D &v2);
                                                                                                      ^

---

C:\Qt\5.15.1\mingw81_64\include\QtGui\qbrush.h:50: In file included from C:\Qt\5.15.1\mingw81_64\include/QtGui/qbrush.h:50,
In file included from C:\Qt\5.15.1\mingw81_64\include/QtGui/qbrush.h:50,
                 from C:\Qt\5.15.1\mingw81_64\include/QtGui/qpalette.h:46,
                 from C:\Qt\5.15.1\mingw81_64\include/QtWidgets/qwidget.h:48,
                 from C:\Qt\5.15.1\mingw81_64\include\QtWidgets/qmainwindow.h:44,
                 from C:\Qt\5.15.1\mingw81_64\include\QtWidgets/QMainWindow:1,
                 from ..\..\rotortest\App\app.h:4,
                 from ..\..\rotortest\App\app.cpp:1:
C:\Qt\5.15.1\mingw81_64\include/QtGui/qtransform.h:417:19: note: previous definition of 'QTransform operator-(const QTransform&, qreal)' was here
 inline QTransform operator -(const QTransform &a, qreal n)
                   ^~~~~~~~

And others....

Is there a way to remove this warnings on this setup above?

Thank you,

[jsulm]

@fem_dev Do you set C++ standard in your pro file?
Are you sure you really use MingW 8.1 and not another one?

[J.Hilk]

@fem_dev
could be this bug:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89325
MingW 8.4 should have it fixed

[fem_dev]

@jsulm yes! My *.pro file is setting C++ standard.
In this machine I have just one setup installed: MingW 8.1 that comes with Qt 5.15.1 installer.

[fem_dev]

@J-Hilk Is there a way to update my MingW 8.1 to the 8.4 version?

[Christian Ehrlicher]

Simply add '-Wno-attributes' to your compiler flags.