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/Gui/AutoSaver.cpp

@@ -145,7 +145,9 @@ void AutoSaver::saveDocument(const std::string& name, AutoSaveProperty& saver)
             .arg(QString::fromUtf8(doc->TransientDir.getValue())));
         if (file.open(QFile::WriteOnly)) {
             QTextStream str(&file);
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
             str.setCodec("UTF-8");
+#endif
             str << "<?xml version='1.0' encoding='utf-8'?>\n"
                 << "<AutoRecovery SchemaVersion=\"1\">\n";
             str << "  <Status>Created</Status>\n";

src/Gui/ComboView.cpp

@@ -50,7 +50,7 @@ ComboView::ComboView(bool showModel, Gui::Document* pcDocument, QWidget *parent)
 
     auto pLayout = new QGridLayout(this);
     pLayout->setSpacing( 0 );
-    pLayout->setMargin ( 0 );
+    pLayout->setContentsMargins ( 0, 0, 0, 0 );
 
     // tabs to switch between Tree/Properties and TaskPanel
     tabs = new QTabWidget ();

src/Gui/DlgCustomizeImp.cpp

@@ -59,11 +59,11 @@ DlgCustomizeImp::DlgCustomizeImp(QWidget* parent, Qt::WindowFlags fl)
 
     customLayout = new QGridLayout( this );
     customLayout->setSpacing( 6 );
-    customLayout->setMargin( 11 );
+    customLayout->setContentsMargins( 11, 11, 11, 11 );
 
     layout = new QHBoxLayout;
     layout->setSpacing( 6 );
-    layout->setMargin( 0 );
+    layout->setContentsMargins( 0, 0, 0, 0 );
 
     buttonHelp = new QPushButton( this );
     buttonHelp->setText(tr("&Help"));

src/Gui/DocumentModel.cpp

@@ -268,9 +268,7 @@ namespace Gui {
             Document* doc = Application::Instance->activeDocument();
             QFont font;
             font.setBold(doc==&d);
-            QVariant variant;
-            variant.setValue<QFont>(font);
-            return variant;
+            return static_cast<QVariant>(font);
         }
 
         return QVariant();
@@ -325,9 +323,7 @@ namespace Gui {
             App::DocumentObject* act = obj->getDocument()->getActiveObject();
             QFont font;
             font.setBold(obj==act);
-            QVariant variant;
-            variant.setValue<QFont>(font);
-            return variant;
+            return static_cast<QVariant>(font);
         }
 
         return QVariant();

src/Gui/DocumentRecovery.cpp

@@ -355,7 +355,9 @@ void DocumentRecoveryPrivate::writeRecoveryInfo(const DocumentRecoveryPrivate::I
     QFile file(info.xmlFile);
     if (file.open(QFile::WriteOnly)) {
         QTextStream str(&file);
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
         str.setCodec("UTF-8");
+#endif
         str << "<?xml version='1.0' encoding='utf-8'?>\n"
             << "<AutoRecovery SchemaVersion=\"1\">\n";
         switch (info.status) {

src/Gui/EditorView.cpp

@@ -113,7 +113,7 @@ EditorView::EditorView(QPlainTextEdit* editor, QWidget* parent)
     hbox->setFrameShape(QFrame::StyledPanel);
     hbox->setFrameShadow(QFrame::Sunken);
     auto layout = new QVBoxLayout();
-    layout->setMargin(1);
+    layout->setContentsMargins(1, 1, 1, 1);
     layout->addWidget(d->textEdit);
     layout->addWidget(d->searchBar);
     d->textEdit->setParent(hbox);

src/Gui/FileDialog.cpp

@@ -662,7 +662,7 @@ FileChooser::FileChooser ( QWidget * parent )
   , _filter( QString() )
 {
     auto layout = new QHBoxLayout( this );
-    layout->setMargin( 0 );
+    layout->setContentsMargins( 0, 0, 0, 0 );
     layout->setSpacing( 2 );
 
     lineEdit = new QLineEdit ( this );
@@ -856,11 +856,11 @@ SelectModule::SelectModule (const QString& type, const SelectModule::Dict& types
     group = new QButtonGroup(this);
     gridLayout = new QGridLayout(this);
     gridLayout->setSpacing(6);
-    gridLayout->setMargin(9);
+    gridLayout->setContentsMargins(9, 9, 9, 9);
 
     gridLayout1 = new QGridLayout(groupBox);
     gridLayout1->setSpacing(6);
-    gridLayout1->setMargin(9);
+    gridLayout1->setContentsMargins(9, 9, 9, 9);
 
     int index = 0;
     for (SelectModule::Dict::const_iterator it = types.begin(); it != types.end(); ++it) {
@@ -897,7 +897,7 @@ SelectModule::SelectModule (const QString& type, const SelectModule::Dict& types
 
     hboxLayout = new QHBoxLayout();
     hboxLayout->setSpacing(6);
-    hboxLayout->setMargin(0);
+    hboxLayout->setContentsMargins(0, 0, 0, 0);
     spacerItem1 = new QSpacerItem(131, 31, QSizePolicy::Expanding, QSizePolicy::Minimum);
     hboxLayout->addItem(spacerItem1);
 

src/Gui/Flag.cpp

@@ -183,7 +183,7 @@ QSize Flag::sizeHint() const
 FlagLayout::FlagLayout(QWidget *parent, int margin, int spacing)
     : QLayout(parent)
 {
-    setMargin(margin);
+    setContentsMargins(margin, margin, margin, margin);
     setSpacing(spacing);
 }
 

src/Gui/GuiApplication.cpp

@@ -62,7 +62,9 @@ GUIApplication::GUIApplication(int & argc, char ** argv)
 {
     connect(this, SIGNAL(commitDataRequest(QSessionManager &)),
             SLOT(commitData(QSessionManager &)), Qt::DirectConnection);
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
     setFallbackSessionManagementEnabled(false);
+#endif
 }
 
 GUIApplication::~GUIApplication()

src/Gui/ManualAlignment.cpp

@@ -394,7 +394,7 @@ class AlignmentView : public Gui::AbstractSplitView
 
         auto vbox = new QFrame(this);
         auto layout = new QVBoxLayout();
-        layout->setMargin(0);
+        layout->setContentsMargins(0, 0, 0, 0);
         layout->setSpacing(0);
         vbox->setLayout(layout);
 

src/Gui/PropertyView.cpp

@@ -72,7 +72,7 @@ PropertyView::PropertyView(QWidget *parent)
 {
     auto pLayout = new QGridLayout( this );
     pLayout->setSpacing(0);
-    pLayout->setMargin (0);
+    pLayout->setContentsMargins(0, 0, 0, 0);
 
     timer = new QTimer(this);
     timer->setSingleShot(true);
@@ -560,7 +560,7 @@ PropertyDockView::PropertyDockView(Gui::Document* pcDocument, QWidget *parent)
     auto view = new PropertyView(this);
     auto pLayout = new QGridLayout(this);
     pLayout->setSpacing(0);
-    pLayout->setMargin (0);
+    pLayout->setContentsMargins(0, 0, 0, 0);
     pLayout->addWidget(view, 0, 0);
 
     resize( 200, 400 );

src/Gui/QSint/actionpanel/actiongroup.cpp

@@ -45,7 +45,7 @@ void ActionGroup::init(bool header)
   myScheme = ActionPanelScheme::defaultScheme();
 
   QVBoxLayout *vbl = new QVBoxLayout();
-  vbl->setMargin(0);
+  vbl->setContentsMargins(0, 0, 0, 0);
   vbl->setSpacing(0);
   setLayout(vbl);
 

src/Gui/QSint/actionpanel/actionpanel.cpp

@@ -26,7 +26,7 @@ ActionPanel::ActionPanel(QWidget *parent) :
     setSizePolicy(QSizePolicy::Maximum, QSizePolicy::Preferred);
 
     QVBoxLayout *vbl = new QVBoxLayout();
-    vbl->setMargin(8);
+    vbl->setContentsMargins(8, 8, 8, 8);
     vbl->setSpacing(8);
     setLayout(vbl);
 }

src/Gui/QSint/actionpanel/taskgroup_p.cpp

@@ -25,7 +25,7 @@ TaskGroup::TaskGroup(QWidget *parent, bool hasHeader)
     setScheme(ActionPanelScheme::defaultScheme());
 
     QVBoxLayout *vbl = new QVBoxLayout();
-    vbl->setMargin(4);
+    vbl->setContentsMargins(4, 4, 4, 4);
     vbl->setSpacing(0);
     setLayout(vbl);
 
@@ -63,7 +63,7 @@ bool TaskGroup::addWidget(QWidget *widget, bool addToLayout, bool addStretch)
 
   if (addStretch) {
     QHBoxLayout *hbl = new QHBoxLayout();
-    hbl->setMargin(0);
+    hbl->setContentsMargins(0, 0, 0, 0);
     hbl->setSpacing(0);
     hbl->addWidget(widget);
     hbl->addStretch();

src/Gui/QSint/actionpanel/taskheader_p.cpp

@@ -40,7 +40,7 @@ TaskHeader::TaskHeader(const QIcon &icon, const QString &title, bool expandable,
     connect(myTitle, SIGNAL(clicked()), this, SLOT(fold()));
 
     QHBoxLayout *hbl = new QHBoxLayout();
-    hbl->setMargin(2);
+    hbl->setContentsMargins(2, 2, 2, 2);
     setLayout(hbl);
 
     hbl->addWidget(myTitle);

src/Gui/ReportView.cpp

@@ -60,7 +60,7 @@ ReportView::ReportView( QWidget* parent )
     resize( 529, 162 );
     auto tabLayout = new QGridLayout( this );
     tabLayout->setSpacing( 0 );
-    tabLayout->setMargin( 0 );
+    tabLayout->setContentsMargins( 0, 0, 0, 0 );
 
     tabWidget = new QTabWidget( this );
     tabWidget->setObjectName(QString::fromUtf8("tabWidget"));

src/Gui/SelectionView.cpp

@@ -62,7 +62,7 @@ SelectionView::SelectionView(Gui::Document* pcDocument, QWidget *parent)
 
     QVBoxLayout* vLayout = new QVBoxLayout(this);
     vLayout->setSpacing(0);
-    vLayout->setMargin (0);
+    vLayout->setContentsMargins(0, 0, 0, 0);
 
     QLineEdit* searchBox = new QLineEdit(this);
     searchBox->setPlaceholderText(tr("Search"));

src/Gui/Splashscreen.cpp

@@ -412,7 +412,9 @@ void AboutDialog::showCredits()
     creditsHTML += QString::fromLatin1("</h2><ul>");
 
     QTextStream stream(&creditsFile);
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
     stream.setCodec("UTF-8");
+#endif
     QString line;
     while (stream.readLineInto(&line)) {
         if (!line.isEmpty()) {

src/Gui/Thumbnail.cpp

@@ -116,7 +116,7 @@ void Thumbnail::SaveDocFile (Base::Writer &writer) const
 
     if (!px.isNull()) {
         // according to specification add some meta-information to the image
-        uint mt = QDateTime::currentDateTimeUtc().toTime_t();
+        qint64 mt = QDateTime::currentDateTimeUtc().toSecsSinceEpoch();
         QString mtime = QString::fromLatin1("%1").arg(mt);
         img.setText(QLatin1String("Software"), qApp->applicationName());
         img.setText(QLatin1String("Thumb::Mimetype"), QLatin1String("application/x-extension-fcstd"));

src/Gui/Tree.cpp

@@ -1489,11 +1489,6 @@ void TreeWidget::startDrag(Qt::DropActions supportedActions)
     }
 }
 
-QMimeData* TreeWidget::mimeData(const QList<QTreeWidgetItem*> items) const
-{
-    return QTreeWidget::mimeData(items);
-}
-
 bool TreeWidget::dropMimeData(QTreeWidgetItem* parent, int index,
     const QMimeData* data, Qt::DropAction action)
 {
@@ -3028,7 +3023,7 @@ TreePanel::TreePanel(const char* name, QWidget* parent)
 
     auto pLayout = new QVBoxLayout(this);
     pLayout->setSpacing(0);
-    pLayout->setMargin(0);
+    pLayout->setContentsMargins(0, 0, 0, 0);
     pLayout->addWidget(this->treeWidget);
     connect(this->treeWidget, SIGNAL(emitSearchObjects()),
         this, SLOT(showEditor()));
@@ -3116,7 +3111,7 @@ TreeDockWidget::TreeDockWidget(Gui::Document* pcDocument, QWidget* parent)
     auto panel = new TreePanel("TreeView", this);
     auto pLayout = new QGridLayout(this);
     pLayout->setSpacing(0);
-    pLayout->setMargin(0);
+    pLayout->setContentsMargins(0, 0, 0, 0);
     pLayout->addWidget(panel, 0, 0);
 }
 

src/Gui/Tree.h

@@ -124,7 +124,6 @@ class TreeWidget : public QTreeWidget, public SelectionObserver
     bool dropMimeData(QTreeWidgetItem *parent, int index, const QMimeData *data,
                       Qt::DropAction action) override;
     Qt::DropActions supportedDropActions () const override;
-    QMimeData * mimeData (const QList<QTreeWidgetItem *> items) const override;
     void dragEnterEvent(QDragEnterEvent * event) override;
     void dragLeaveEvent(QDragLeaveEvent * event) override;
     void dragMoveEvent(QDragMoveEvent *event) override;

src/Gui/Widgets.cpp

@@ -1046,7 +1046,7 @@ LabelButton::LabelButton (QWidget * parent)
   : QWidget(parent)
 {
     auto layout = new QHBoxLayout(this);
-    layout->setMargin(0);
+    layout->setContentsMargins(0, 0, 0, 0);
     layout->setSpacing(1);
 
     label = new QLabel(this);
@@ -1202,7 +1202,7 @@ StatusWidget::StatusWidget(QWidget* parent)
 
     auto gridLayout = new QGridLayout(this);
     gridLayout->setSpacing(6);
-    gridLayout->setMargin(9);
+    gridLayout->setContentsMargins(9, 9, 9, 9);
     gridLayout->addWidget(label, 0, 0, 1, 1);
 }
 
@@ -1411,7 +1411,7 @@ LabelEditor::LabelEditor (QWidget * parent)
 {
     type = String;
     auto layout = new QHBoxLayout(this);
-    layout->setMargin(0);
+    layout->setContentsMargins(0, 0, 0, 0);
     layout->setSpacing(2);
 
     lineEdit = new QLineEdit(this);

src/Gui/propertyeditor/PropertyItem.cpp

@@ -1506,7 +1506,7 @@ PropertyEditorWidget::PropertyEditorWidget (QWidget * parent)
   : QWidget(parent)
 {
     auto layout = new QHBoxLayout(this);
-    layout->setMargin(0);
+    layout->setContentsMargins(0, 0, 0, 0);
     layout->setSpacing(2);
 
     lineEdit = new QLineEdit(this);
@@ -3065,7 +3065,9 @@ void PropertyStringListItem::setValue(const QVariant& value)
     QStringList values = value.toStringList();
     QString data;
     QTextStream str(&data);
+#if QT_VERSION < QT_VERSION_CHECK(6,0,0)
     str.setCodec("UTF-8");
+#endif
 
     str << "[";
     for (QStringList::Iterator it = values.begin(); it != values.end(); ++it) {
@@ -4284,7 +4286,7 @@ LinkLabel::LinkLabel (QWidget * parent, const App::Property *prop)
     : QWidget(parent), objProp(prop), dlg(nullptr)
 {   
     auto layout = new QHBoxLayout(this);
-    layout->setMargin(0);
+    layout->setContentsMargins(0, 0, 0, 0);
     layout->setSpacing(1);
 
     label = new QLabel(this);

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());