Long live QKeyCombination!

C++20 via P1120 is deprecating arithmetic operations between
unrelated enumeration types, and GCC 10 is already complaining.
Hence, these operations might become illegal in C++23 or C++26 at
the latest.

A case of this that affects Qt is in key combinations: a
QKeySequence can be constructed by summing / ORing modifiers and a
key, for instance:

  Qt::CTRL + Qt::Key_A
  Qt::SHIFT | Qt::CTRL | Qt::Key_G (recommended, see below)

The problem is that the modifiers and the key belong to different
enumerations (and there's 2 enumerations for the modifier, and one
for the key).

To solve this: add a dedicated class to represent a combination of
keys, and operators between those enumerations to build instances
of this class.

I would've simply defined operator|, but again docs and pre-existing
code use operator+ as well, so added both to at least tackle simple
cases (modifier + key).

Multiple modifiers create a problem: operator+ between them yields
int, not the corresponding flags type (because operator+ is not
overloaded for this use case):

  Qt::CTRL + Qt::SHIFT + Qt::Key_A
  \__________________/      /
          int              /
           \______________/
                  int

Not only this loses track of the datatypes involved, but it would
also then "add" the key (with NO warnings, now its int + enum, so
it's not mixing enums!) and yielding int again.

I don't want to special-case this; the point of the class is
that int is the wrong datatype. Everything works just fine when
using operator| instead:

  Qt::CTRL | Qt::SHIFT | Qt::Key_A
  \__________________/      /
      Qt::Modifiers        /
           \______________/
            QKeyCombination

So I'm defining operator+ so that the simple cases still work,
but also deprecating it.

Port some code around Qt to the new class. In certain cases,
it's a huge win for clarity. In some others, I've just added
the necessary casts to make it still compile without warnings,
without attempting refactorings.

[ChangeLog][QtCore][QKeyCombination] New class to represent
a combination of a key and zero or more modifiers, to be used
when defining shortcuts or similar.

[ChangeLog][Potentially Source-Incompatible Changes] A keyboard
modifier (such as Qt::CTRL, Qt::AltModifier, etc.) should be
combined with a key (such as Qt::Key_A, Qt::Key_F1, etc.) by using
operator|, not operator+.  The result is now an object of type
QKeyCombination, that stores the key and the modifiers.

Change-Id: I657a3a328232f059023fff69c5031ee31cc91dd6
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

1 files changed, 14 insertions, 0 deletions

diff --git a/src/corelib/serialization/qdatastream.h b/src/corelib/serialization/qdatastream.h
index 19188c3d91..32ccf7d6cc 100644
--- a/src/corelib/serialization/qdatastream.h
+++ b/src/corelib/serialization/qdatastream.h
@@ -43,6 +43,7 @@
 #include <QtCore/qscopedpointer.h>
 #include <QtCore/qiodevicebase.h>
 #include <QtCore/qcontainerfwd.h>
+#include <QtCore/qnamespace.h>
 
 #ifdef Status
 #error qdatastream.h must be included before any header file that defines Status
@@ -510,6 +511,19 @@ inline QDataStreamIfHasOStreamOperators<T1, T2> operator<<(QDataStream& s, const
 }
 #endif
 
+inline QDataStream &operator>>(QDataStream &s, QKeyCombination &combination)
+{
+    int combined;
+    s >> combined;
+    combination = QKeyCombination::fromCombined(combined);
+    return s;
+}
+
+inline QDataStream &operator<<(QDataStream &s, QKeyCombination combination)
+{
+    return s << combination.toCombined();
+}
+
 #endif // QT_NO_DATASTREAM
 
 QT_END_NAMESPACE