refactor: Fix deprecation warnings when building against Qt 5.15

[hebasto]

What's New in Qt 5.15:

To help preparing for the transition to Qt 6, numerous classes and member functions that will be removed from Qt 6.0 have been marked as deprecated in the Qt 5.15 release.

Fixes#36

[promag]

Concept ACK.

[fanquake]

Concept ACK

[hebasto]

Rebased 354b2bd -> 705c1f0 (pr46.01 -> pr46.02) due to the conflict with #35.

[Sjors]

As mentioned in #36 I don't see any deprecation warnings on macOS with homebrew QT 5.15, but at least this change doesn't introduce new issues for me.

[hebasto]

@vasild
As you mention these warnings in bitcoin/bitcoin#19716 (comment), mind looking into this PR?

[promag]

Tested ACK 705c1f0 on macos with Apple clang version 11.0.3 (clang-1103.0.32.62) and brew qt 5.15.1.

[jonasschnelli]

utACK 705c1f0
Added 0.22 milestone.

[maflcko]

Concept aCK

[maflcko]

nit: Could pass by reference?

Suggested change

	QImage GetImage(const QLabel* label)
	QImage GetImage(const QLabel& label)

[maflcko]

btw, I am getting a ton of warnings like this one:

 CXX qt/libbitcoinqt_a-bantablemodel.o
In file included from qt/bantablemodel.cpp:5:
In file included from ./qt/bantablemodel.h:12:
In file included from /usr/include/qt5/QtCore/QAbstractTableModel:1:
/usr/include/qt5/QtCore/qabstractitemmodel.h:170:5: warning: 'metaObject' overrides a member function but is not marked 'override' [-Wsuggest-override]
Q_OBJECT
^
/usr/include/qt5/QtCore/qobjectdefs.h:175:32: note: expanded from macro 'Q_OBJECT'
virtual const QMetaObject *metaObject() const; \
^
/usr/include/qt5/QtCore/qobject.h:129:5: note: overridden virtual function is here
Q_OBJECT
^
/usr/include/qt5/QtCore/qobjectdefs.h:175:32: note: expanded from macro 'Q_OBJECT'
virtual const QMetaObject *metaObject() const; \
^

[hebasto]

Compiling on macOS 11.0.1 Big Sur (20B29) + Qt 5.15.1 gives the following warnings now:

• a load of -W#pragma-messages from boost 1.74.0

/usr/local/include/boost/function_output_iterator.hpp:14:1: warning: This header is deprecated. Use <boost/iterator/function_output_iterator.hpp> instead. [-W#pragma-messages]
BOOST_HEADER_DEPRECATED("<boost/iterator/function_output_iterator.hpp>")

• three -Wdeprecated-declarations about deprecated NSUserNotification (see RFC: Migration from NSUserNotificationCenter to UNUserNotificationCenter on macOS #112 and macOS: Post user notifications using QSystemTrayIcon #114)

warning: 'NSUserNotification' is deprecated: first deprecated in macOS 11.0 - All NSUserNotifications API should be replaced with UserNotifications.frameworks API [-Wdeprecated-declarations]

• and

qt/guiutil.cpp:70:37: warning: 'SystemLocaleShortDate' is deprecated: Use QLocale [-Wdeprecated-declarations]
return date.date().toString(Qt::SystemLocaleShortDate) + QString(" ") + date.toString("hh:mm");
^
/usr/local/Cellar/qt/5.15.1/lib/QtCore.framework/Headers/qnamespace.h:1280:31: note: 'SystemLocaleShortDate' has been explicitly marked deprecated here
SystemLocaleShortDate Q_DECL_ENUMERATOR_DEPRECATED_X("Use QLocale"),
^
/usr/local/Cellar/qt/5.15.1/lib/QtCore.framework/Headers/qcompilerdetection.h:1161:45: note: expanded from macro 'Q_DECL_ENUMERATOR_DEPRECATED_X'
# define Q_DECL_ENUMERATOR_DEPRECATED_X(x) Q_DECL_DEPRECATED_X(x)
^
/usr/local/Cellar/qt/5.15.1/lib/QtCore.framework/Headers/qcompilerdetection.h:675:55: note: expanded from macro 'Q_DECL_DEPRECATED_X'
# define Q_DECL_DEPRECATED_X(text) attribute ((__deprecated__(text)))
^
1 warning generated.

Not seening -Wsuggest-override warnings at all 🤷‍♂️

[maflcko]

Oh the override warnings happen with clang on linux. E.g fedora or debian:

https://cirrus-ci.com/task/6217749342978048?command=make#L10798