Qt6 port:

* QApplication::setFallbackSessionManagementEnabled has been removed
* QString::medRef() has been removed. Use QString::mid() again.
* QTextStream::setCodec has been removed
* Use operator QVariant of the QFont class to make code Qt5 and Qt6 compatible
* Signature of QTreeWidget::mimeData() has changed in Qt6. Remove TreeWidget::mimeData() because it doesn't change the implementation
* QLayout::setMargin() is deprecated in Qt5 and has been removed in Qt6. Use QLayout::setContentsMargins()
* QDateTime::toTime_t() is deprecated in Qt5 and has been removed in Qt6. Use QDateTime::toSecsSinceEpoch()
* QDesktopWidget is deprecated in Qt5 and has been removed in Qt6. Use QScreen

src/Mod/Part/App/FaceMakerCheese.cpp

@@ -22,6 +22,7 @@
 
 #include "PreCompiled.h"
 #ifndef _PreComp_
+# include <algorithm>
 # include <Bnd_Box.hxx>
 # include <BRep_Builder.hxx>
 # include <BRep_Tool.hxx>

src/Mod/Part/Gui/DlgFilletEdges.cpp

@@ -429,7 +429,7 @@ void DlgFilletEdges::onSelectEdge(const QString& subelement, int type)
 void DlgFilletEdges::onSelectEdgesOfFace(const QString& subelement, int type)
 {
     bool ok;
-    int index = subelement.midRef(4).toInt(&ok);
+    int index = subelement.mid(4).toInt(&ok);
     if (ok) {
         try {
             const TopoDS_Shape& face = d->all_faces.FindKey(index);

src/Mod/PartDesign/Gui/TaskExtrudeParameters.cpp

@@ -735,9 +735,7 @@ void TaskExtrudeParameters::translateFaceName()
 
         if (ok) {
             ui->lineFaceName->setText(QString::fromLatin1("%1:%2%3")
-                                      .arg(parts[0],
-                                           tr("Face"),
-                                           QString(faceId)));
+                                      .arg(parts[0], tr("Face")).arg(faceId));
         }
         else {
             ui->lineFaceName->setText(parts[0]);

src/Mod/Sketcher/Gui/SketcherSettings.cpp

@@ -51,7 +51,7 @@ SketcherSettings::SketcherSettings(QWidget* parent)
     ui->setupUi(this);
     QGridLayout* gridLayout = new QGridLayout(ui->placeholder);
     gridLayout->setSpacing(0);
-    gridLayout->setMargin(0);
+    gridLayout->setContentsMargins(0, 0, 0, 0);
     form = new SketcherGeneralWidget(ui->placeholder);
     gridLayout->addWidget(form, 0, 0, 1, 1);
 }

src/Mod/Sketcher/Gui/SoDatumLabel.cpp

@@ -36,7 +36,6 @@
 # include <cfloat>
 # include <algorithm>
 # include <QFontMetrics>
-# include <QGLWidget>
 # include <QPainter>
 # include <QPen>
 # include <Inventor/SoPrimitiveVertex.h>
@@ -113,7 +112,7 @@ void SoDatumLabel::drawImage()
         return;
     }
 
-    QFont font(QString::fromLatin1(name.getValue()), size.getValue());
+    QFont font(QString::fromLatin1(name.getValue(), -1), size.getValue());
     QFontMetrics fm(font);
     QString str = QString::fromUtf8(s[0].getString());
 

src/Mod/Sketcher/Gui/ViewProviderSketch.cpp

@@ -39,13 +39,13 @@
 # include <QAction>
 # include <QApplication>
 # include <QColor>
-# include <QDesktopWidget>
 # include <QDialog>
 # include <QFont>
 # include <QKeyEvent>
 # include <QMenu>
 # include <QMessageBox>
 # include <QPainter>
+# include <QScreen>
 # include <QTextStream>
 #endif
 
@@ -3629,7 +3629,7 @@ int ViewProviderSketch::defaultFontSizePixels() const
 }
 
 int ViewProviderSketch::getApplicationLogicalDPIX() const {
-    return QApplication::desktop()->logicalDpiX();
+    return int(QApplication::primaryScreen()->logicalDotsPerInchX());
 }
 
 int ViewProviderSketch::getViewOrientationFactor() const {

src/Mod/Spreadsheet/Gui/qtcolorpicker.cpp

@@ -46,7 +46,7 @@
 ****************************************************************************/
 
 #include <QApplication>
-#include <QDesktopWidget>
+#include <QScreen>
 #include <QPainter>
 #include <QPushButton>
 #include <QColorDialog>
@@ -315,7 +315,7 @@ void QtColorPicker::buttonPressed(bool toggled)
     if (!toggled)
         return;
 
-    const QRect desktop = QApplication::activeWindow()->geometry();
+    const QRect desktop = QApplication::primaryScreen()->geometry();
 
     // Make sure the popup is inside the desktop.
     QPoint pos = mapToGlobal(rect().bottomLeft());
@@ -872,7 +872,7 @@ void ColorPickerPopup::regenerateGrid()
     // one.
     if (grid) delete grid;
     grid = new QGridLayout(this);
-    grid->setMargin(1);
+    grid->setContentsMargins(1, 1, 1, 1);
     grid->setSpacing(0);
 
     int ccol = 0, crow = 0;