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>

3 files changed, 14 insertions, 14 deletions

diff --git a/examples/widgets/desktop/screenshot/screenshot.cpp b/examples/widgets/desktop/screenshot/screenshot.cpp
index af344db1d2..522b1123b5 100644
--- a/examples/widgets/desktop/screenshot/screenshot.cpp
+++ b/examples/widgets/desktop/screenshot/screenshot.cpp
@@ -90,7 +90,7 @@ Screenshot::Screenshot()
     connect(saveScreenshotButton, &QPushButton::clicked, this, &Screenshot::saveScreenshot);
     buttonsLayout->addWidget(saveScreenshotButton);
     QPushButton *quitScreenshotButton = new QPushButton(tr("Quit"), this);
-    quitScreenshotButton->setShortcut(Qt::CTRL + Qt::Key_Q);
+    quitScreenshotButton->setShortcut(Qt::CTRL | Qt::Key_Q);
     connect(quitScreenshotButton, &QPushButton::clicked, this, &QWidget::close);
     buttonsLayout->addWidget(quitScreenshotButton);
     buttonsLayout->addStretch();
diff --git a/examples/widgets/itemviews/storageview/main.cpp b/examples/widgets/itemviews/storageview/main.cpp
index 8f23a4820a..fe916b039d 100644
--- a/examples/widgets/itemviews/storageview/main.cpp
+++ b/examples/widgets/itemviews/storageview/main.cpp
@@ -66,7 +66,7 @@ int main(int argc, char *argv[])
 
     StorageModel *model = new StorageModel(&view);
     model->refresh();
-    QShortcut *refreshShortcut = new QShortcut(Qt::CTRL + Qt::Key_R, &view);
+    QShortcut *refreshShortcut = new QShortcut(Qt::CTRL | Qt::Key_R, &view);
     QObject::connect(refreshShortcut, &QShortcut::activated, model, &StorageModel::refresh);
     view.setModel(model);
 
diff --git a/examples/widgets/richtext/textedit/textedit.cpp b/examples/widgets/richtext/textedit/textedit.cpp
index 9504c8769d..74b8e1c2b4 100644
--- a/examples/widgets/richtext/textedit/textedit.cpp
+++ b/examples/widgets/richtext/textedit/textedit.cpp
@@ -209,14 +209,14 @@ void TextEdit::setupFileActions()
     const QIcon exportPdfIcon = QIcon::fromTheme("exportpdf", QIcon(rsrcPath + "/exportpdf.png"));
     a = menu->addAction(exportPdfIcon, tr("&Export PDF..."), this, &TextEdit::filePrintPdf);
     a->setPriority(QAction::LowPriority);
-    a->setShortcut(Qt::CTRL + Qt::Key_D);
+    a->setShortcut(Qt::CTRL | Qt::Key_D);
     tb->addAction(a);
 
     menu->addSeparator();
 #endif
 
     a = menu->addAction(tr("&Quit"), this, &QWidget::close);
-    a->setShortcut(Qt::CTRL + Qt::Key_Q);
+    a->setShortcut(Qt::CTRL | Qt::Key_Q);
 }
 
 void TextEdit::setupEditActions()
@@ -266,7 +266,7 @@ void TextEdit::setupTextActions()
 
     const QIcon boldIcon = QIcon::fromTheme("format-text-bold", QIcon(rsrcPath + "/textbold.png"));
     actionTextBold = menu->addAction(boldIcon, tr("&Bold"), this, &TextEdit::textBold);
-    actionTextBold->setShortcut(Qt::CTRL + Qt::Key_B);
+    actionTextBold->setShortcut(Qt::CTRL | Qt::Key_B);
     actionTextBold->setPriority(QAction::LowPriority);
     QFont bold;
     bold.setBold(true);
@@ -277,7 +277,7 @@ void TextEdit::setupTextActions()
     const QIcon italicIcon = QIcon::fromTheme("format-text-italic", QIcon(rsrcPath + "/textitalic.png"));
     actionTextItalic = menu->addAction(italicIcon, tr("&Italic"), this, &TextEdit::textItalic);
     actionTextItalic->setPriority(QAction::LowPriority);
-    actionTextItalic->setShortcut(Qt::CTRL + Qt::Key_I);
+    actionTextItalic->setShortcut(Qt::CTRL | Qt::Key_I);
     QFont italic;
     italic.setItalic(true);
     actionTextItalic->setFont(italic);
@@ -286,7 +286,7 @@ void TextEdit::setupTextActions()
 
     const QIcon underlineIcon = QIcon::fromTheme("format-text-underline", QIcon(rsrcPath + "/textunder.png"));
     actionTextUnderline = menu->addAction(underlineIcon, tr("&Underline"), this, &TextEdit::textUnderline);
-    actionTextUnderline->setShortcut(Qt::CTRL + Qt::Key_U);
+    actionTextUnderline->setShortcut(Qt::CTRL | Qt::Key_U);
     actionTextUnderline->setPriority(QAction::LowPriority);
     QFont underline;
     underline.setUnderline(true);
@@ -298,31 +298,31 @@ void TextEdit::setupTextActions()
 
     const QIcon leftIcon = QIcon::fromTheme("format-justify-left", QIcon(rsrcPath + "/textleft.png"));
     actionAlignLeft = new QAction(leftIcon, tr("&Left"), this);
-    actionAlignLeft->setShortcut(Qt::CTRL + Qt::Key_L);
+    actionAlignLeft->setShortcut(Qt::CTRL | Qt::Key_L);
     actionAlignLeft->setCheckable(true);
     actionAlignLeft->setPriority(QAction::LowPriority);
     const QIcon centerIcon = QIcon::fromTheme("format-justify-center", QIcon(rsrcPath + "/textcenter.png"));
     actionAlignCenter = new QAction(centerIcon, tr("C&enter"), this);
-    actionAlignCenter->setShortcut(Qt::CTRL + Qt::Key_E);
+    actionAlignCenter->setShortcut(Qt::CTRL | Qt::Key_E);
     actionAlignCenter->setCheckable(true);
     actionAlignCenter->setPriority(QAction::LowPriority);
     const QIcon rightIcon = QIcon::fromTheme("format-justify-right", QIcon(rsrcPath + "/textright.png"));
     actionAlignRight = new QAction(rightIcon, tr("&Right"), this);
-    actionAlignRight->setShortcut(Qt::CTRL + Qt::Key_R);
+    actionAlignRight->setShortcut(Qt::CTRL | Qt::Key_R);
     actionAlignRight->setCheckable(true);
     actionAlignRight->setPriority(QAction::LowPriority);
     const QIcon fillIcon = QIcon::fromTheme("format-justify-fill", QIcon(rsrcPath + "/textjustify.png"));
     actionAlignJustify = new QAction(fillIcon, tr("&Justify"), this);
-    actionAlignJustify->setShortcut(Qt::CTRL + Qt::Key_J);
+    actionAlignJustify->setShortcut(Qt::CTRL | Qt::Key_J);
     actionAlignJustify->setCheckable(true);
     actionAlignJustify->setPriority(QAction::LowPriority);
     const QIcon indentMoreIcon = QIcon::fromTheme("format-indent-more", QIcon(rsrcPath + "/format-indent-more.png"));
     actionIndentMore = menu->addAction(indentMoreIcon, tr("&Indent"), this, &TextEdit::indent);
-    actionIndentMore->setShortcut(Qt::CTRL + Qt::Key_BracketRight);
+    actionIndentMore->setShortcut(Qt::CTRL | Qt::Key_BracketRight);
     actionIndentMore->setPriority(QAction::LowPriority);
     const QIcon indentLessIcon = QIcon::fromTheme("format-indent-less", QIcon(rsrcPath + "/format-indent-less.png"));
     actionIndentLess = menu->addAction(indentLessIcon, tr("&Unindent"), this, &TextEdit::unindent);
-    actionIndentLess->setShortcut(Qt::CTRL + Qt::Key_BracketLeft);
+    actionIndentLess->setShortcut(Qt::CTRL | Qt::Key_BracketLeft);
     actionIndentLess->setPriority(QAction::LowPriority);
 
     // Make sure the alignLeft  is always left of the alignRight
@@ -358,7 +358,7 @@ void TextEdit::setupTextActions()
 
     const QIcon checkboxIcon = QIcon::fromTheme("status-checkbox-checked", QIcon(rsrcPath + "/checkbox-checked.png"));
     actionToggleCheckState = menu->addAction(checkboxIcon, tr("Chec&ked"), this, &TextEdit::setChecked);
-    actionToggleCheckState->setShortcut(Qt::CTRL + Qt::Key_K);
+    actionToggleCheckState->setShortcut(Qt::CTRL | Qt::Key_K);
     actionToggleCheckState->setCheckable(true);
     actionToggleCheckState->setPriority(QAction::LowPriority);
     tb->addAction(actionToggleCheckState);