Fix possible crash in CalendarBox.

If month change notification was posted async there was a possibility
to get a mousePressEvent() with already new Context field values, but
with old _selected value. Those two could be inconsistent leading to
an assert violation in (_selected + _context->daysShift() >= 0).

Telegram/SourceFiles/boxes/calendar_box.cpp

@@ -117,11 +117,6 @@ void CalendarBox::Context::showMonth(QDate month) {
 }
 
 void CalendarBox::Context::applyMonth(const QDate &month, bool forced) {
-	if (forced) {
-		_month.setForced(month);
-	} else {
-		_month.set(month);
-	}
 	_daysCount = month.daysInMonth();
 	_daysShift = daysShiftForMonth(month);
 	_rowsCount = rowsCountForMonth(month);
@@ -130,6 +125,11 @@ void CalendarBox::Context::applyMonth(const QDate &month, bool forced) {
 	_highlightedIndex = month.daysTo(_highlighted);
 	_minDayIndex = _min.isNull() ? INT_MIN : month.daysTo(_min);
 	_maxDayIndex = _max.isNull() ? INT_MAX : month.daysTo(_max);
+	if (forced) {
+		_month.setForced(month, true);
+	} else {
+		_month.set(month, true);
+	}
 }
 
 void CalendarBox::Context::skipMonth(int skip) {
@@ -219,6 +219,7 @@ protected:
 
 private:
 	void monthChanged(QDate month);
+	void setSelected(int selected);
 	void setPressed(int pressed);
 
 	int rowsLeft() const;
@@ -239,16 +240,21 @@ private:
 
 };
 
-CalendarBox::Inner::Inner(QWidget *parent, Context *context) : TWidget(parent)
+CalendarBox::Inner::Inner(QWidget *parent, Context *context)
+: TWidget(parent)
 , _context(context) {
 	setMouseTracking(true);
-	subscribe(context->month(), [this](QDate month) { monthChanged(month); });
+	subscribe(context->month(), [this](QDate month) {
+		monthChanged(month);
+	});
 }
 
 void CalendarBox::Inner::monthChanged(QDate month) {
+	setSelected(kEmptySelection);
 	_ripples.clear();
 	resizeToCurrent();
 	update();
+	sendSynteticMouseEvent(this, QEvent::MouseMove, Qt::NoButton);
 }
 
 void CalendarBox::Inner::resizeToCurrent() {
@@ -343,19 +349,33 @@ void CalendarBox::Inner::paintRows(Painter &p, QRect clip) {
 }
 
 void CalendarBox::Inner::mouseMoveEvent(QMouseEvent *e) {
-	auto point = e->pos();
+	const auto size = st::calendarCellSize;
-	auto row = floorclamp(point.y() - rowsTop(), st::calendarCellSize.height(), 0, _context->rowsCount());
+	const auto point = e->pos();
-	auto col = floorclamp(point.x() - rowsLeft(), st::calendarCellSize.width(), 0, kDaysInWeek);
+	const auto inner = QRect(
-	auto index = row * kDaysInWeek + col - _context->daysShift();
+		rowsLeft(),
-	if (_context->isEnabled(index)) {
+		rowsTop(),
-		_selected = index;
+		kDaysInWeek * size.width(),
-		setCursor(style::cur_pointer);
+		_context->rowsCount() * size.height());
+	if (inner.contains(point)) {
+		const auto row = (point.y() - rowsTop()) / size.height();
+		const auto col = (point.x() - rowsLeft()) / size.width();
+		const auto index = row * kDaysInWeek + col - _context->daysShift();
+		setSelected(index);
 	} else {
-		_selected = kEmptySelection;
+		setSelected(kEmptySelection);
-		setCursor(style::cur_default);
 	}
 }
 
+void CalendarBox::Inner::setSelected(int selected) {
+	if (selected != kEmptySelection && !_context->isEnabled(selected)) {
+		selected = kEmptySelection;
+	}
+	_selected = selected;
+	setCursor((_selected == kEmptySelection)
+		? style::cur_default
+		: style::cur_pointer);
+}
+
 void CalendarBox::Inner::mousePressEvent(QMouseEvent *e) {
 	setPressed(_selected);
 	if (_selected != kEmptySelection) {
@@ -400,7 +420,9 @@ CalendarBox::Inner::~Inner() = default;
 
 class CalendarBox::Title : public TWidget, private base::Subscriber {
 public:
-	Title(QWidget *parent, Context *context) : TWidget(parent), _context(context) {
+	Title(QWidget *parent, Context *context)
+	: TWidget(parent)
+	, _context(context) {
 		subscribe(_context->month(), [this](QDate date) { monthChanged(date); });
 	}