Allow compiling with Qt6

This commit allows compiling LyX with Qt6 when using autotools.
For a successful compilation the following 2 conditions must be met.

1) The Qt6 qmake has to come first in PATH, so that the command
   "qmake -v | grep -o 'Qt version .'" returns "Qt version 6".
2) The --enable-qt6 switch has to be passed to the configure command.

If --enable-qt6 is used but Qt6 is not found, Qt5 is tried as a fallback.
If also Qt5 is not found, configuring for Qt4 is attempted.
If --enable-qt6 is not used, then things go as usual. This means that Qt5
is tried first and then Qt4, unless --disable-qt5 is used, in which case
Qt4 is directly attempted. This means that existing scripts should
continue working unmodified.

LyX should compile with Qt6 on windows and linux, and possibly also on
mac, but I could not test that. However, it is not guaranteed that it
works as it should. In particular I am not sure that I got right the
conversion from QRegExp to QRegularExpression. For sure, the syntax
highlighting seems to not work right. Someone in the know should take
a look at that. I am able to load documents and compile them but some
thourough testing is needed. However, when compiling for Qt5 or Qt4,
I tried to make sure that the functionality is preserved.

config/lyxinclude.m4

@@ -63,7 +63,16 @@ AC_MSG_RESULT([$withval])
 ])
 
 
-dnl Check whether to configure for Qt4 or Qt5. Default is Qt5.
+dnl Check whether to configure for Qt4, Qt5, or Qt6. Default is Qt5.
+dnl
+AC_DEFUN([LYX_CHECK_QT6],[
+AC_MSG_CHECKING([whether Qt6 is requested])
+AC_ARG_ENABLE([qt6],
+  [AS_HELP_STRING([--enable-qt6],[use Qt6 for building])],
+  USE_QT6=$enableval, USE_QT6=no)
+AC_MSG_RESULT([$USE_QT6])
+AC_SUBST([USE_QT6])
+])
 dnl
 AC_DEFUN([LYX_CHECK_QT5],[
 AC_MSG_CHECKING([whether Qt5 is disabled])
@@ -372,7 +381,7 @@ if test x$GXX = xyes; then
     AM_CXXFLAGS="$AM_CXXFLAGS -fno-omit-frame-pointer"
   fi
 
-  if test x$USE_QT5 = xyes ; then
+  if test x$USE_QT5 = xyes -o x$USE_QT6 = xyes; then
       AS_CASE([$host], [*mingw*|*cygwin*], [], [AM_CXXFLAGS="-fPIC $AM_CXXFLAGS"])
   fi
   dnl Warnings are for preprocessor too

config/qt.m4

@@ -26,7 +26,10 @@ AC_DEFUN([QT_CHECK_COMPILE],
 		CXXFLAGS="$CXXFLAGS $QT_INCLUDES $QT_LDFLAGS"
 		qt_corelibs="-lQtCore -lQtCore4"
 		qt_guilibs="'-lQtCore -lQtGui' '-lQtCore4 -lQtGui4'"
-		if test $USE_QT5 = "yes" ; then
+		if test $USE_QT6 = "yes" ; then
+		    qt_corelibs="-lQt6Core -lQt6Core5Compat"
+		    qt_guilibs="-lQt6Core -lQt6Core5Compat -lQt6Concurrent -lQt6Gui -lQt6Svg -lQt6Widgets"
+		elif test $USE_QT5 = "yes" ; then
 		    qt_corelibs="-lQt5Core"
 		    qt_guilibs="-lQt5Core -lQt5Concurrent -lQt5Gui -lQt5Svg -lQt5Widgets"
 		fi
@@ -52,7 +55,9 @@ AC_DEFUN([QT_CHECK_COMPILE],
 	])
 
 	if test -z "$qt_cv_libname"; then
-		if test x$USE_QT5 = xyes ; then
+		if test x$USE_QT6 = xyes ; then
+			AC_MSG_RESULT([failed, retrying with Qt5])
+		elif test x$USE_QT5 = xyes ; then
 			AC_MSG_RESULT([failed, retrying with Qt4])
 		else
 			AC_MSG_RESULT([failed])
@@ -68,7 +73,9 @@ AC_DEFUN([QT_FIND_TOOL],
 [
 	$1=
 	qt_ext=qt4
-	if test "x$USE_QT5" != "xno" ; then
+	if test "x$USE_QT6" != "xno" ; then
+		qt_ext=qt6
+	elif test "x$USE_QT5" != "xno" ; then
 		qt_ext=qt5
 	fi
 
@@ -161,17 +168,41 @@ AC_DEFUN([QT_DO_IT_ALL],
 
 	dnl Check if it possible to do a pkg-config
 	PKG_PROG_PKG_CONFIG
-	if test -n "$PKG_CONFIG" ; then
+	dnl Not possible with Qt6 (QTBUG-86080)
-		QT_DO_PKG_CONFIG
+	if test x$USE_QT6 = xno ; then
-	fi
+	    if test -n "$PKG_CONFIG" ; then
-	if test "$pkg_failed" != "no" ; then
+		    QT_DO_PKG_CONFIG
-		QT_DO_MANUAL_CONFIG
+	    fi
+	    if test "$pkg_failed" != "no" ; then
+		    QT_DO_MANUAL_CONFIG
+	    fi
+	else
+	    QT6_QMAKE_CONFIG
+	    if test -z "$QT_LIB"; then
+		    QT_DO_MANUAL_CONFIG
+	    fi
 	fi
 
 	if test -z "$QT_LIB"; then
-	  dnl Try again with Qt4 if configuring for Qt5 fails
+	  dnl Try again with Qt5 and then Qt4 if configuring for Qt6/5 fails
-	  if test x$USE_QT5 = xyes ; then
+	  if test x$USE_QT6 = xyes ; then
+		USE_QT6=no
+		USE_QT5=yes
+		AC_SUBST([USE_QT6])
+		AC_SUBST([USE_QT5])
+		if test -n "$PKG_CONFIG" ; then
+		  QT_DO_PKG_CONFIG
+		fi
+		if test "$pkg_failed" != "no" ; then
+		  QT_DO_MANUAL_CONFIG
+		fi
+		if test -z "$QT_LIB"; then
+		  AC_MSG_ERROR([cannot find qt libraries.])
+		fi
+	  elif test x$USE_QT5 = xyes ; then
+		USE_QT6=no
 		USE_QT5=no
+		AC_SUBST([USE_QT6])
 		AC_SUBST([USE_QT5])
 		if test -n "$PKG_CONFIG" ; then
 		  QT_DO_PKG_CONFIG
@@ -197,8 +228,21 @@ AC_DEFUN([QT_DO_IT_ALL],
 	AC_CHECK_HEADER(QtGui/qtgui-config.h,
 	  [lyx_qt5_config=QtGui/qtgui-config.h],
 	  [lyx_qt5_config=qconfig.h],[-])
+	AC_CHECK_HEADER(QtGui/private/qtgui-config_p.h,
+	  [lyx_qt6_config=QtGui/private/qtgui-config_p.h],
+	  [lyx_qt6_config=qconfig.h],[-])
 	AC_MSG_CHECKING([whether Qt uses the X Window system])
-	if test x$USE_QT5 = xyes ; then
+	if test x$USE_QT6 = xyes ; then
+	  dnl FIXME: Check whether defining QPA_XCB makes sense with Qt6
+	  AC_PREPROC_IFELSE([AC_LANG_SOURCE([
+	    [#include <$lyx_qt6_config>]
+	    [#if !defined(QT_FEATURE_xcb) || QT_FEATURE_xcb < 0]
+	    [#error Fail]
+	    [#endif]])],
+	    [AC_MSG_RESULT(yes)
+	     AC_DEFINE(QPA_XCB, 1, [Define if Qt uses the X Window System])],
+	    [AC_MSG_RESULT(no)])
+	elif test x$USE_QT5 = xyes ; then
 	  AC_EGREP_CPP(xcb,
 	    [#include <$lyx_qt5_config>
 	    QT_QPA_DEFAULT_PLATFORM_NAME],
@@ -351,3 +395,75 @@ AC_DEFUN([QT_DO_MANUAL_CONFIG],
 		QT_GET_VERSION
 	fi
 ])
+
+AC_DEFUN([QT6_QMAKE_CONFIG],
+[
+	AC_MSG_CHECKING([for Qt6])
+	dnl Use first qmake in PATH
+	ver=`qmake -v | grep -o "Qt version ."`
+	if test "$ver" = "Qt version 6"; then
+	    dnl Use a .pro file for getting qmake's variables
+	    lyx_test_qt_dir=`mktemp -d`
+	    lyx_test_qt_pro="$lyx_test_qt_dir/test.pro"
+	    lyx_test_qt_mak="$lyx_test_qt_dir/Makefile"
+	    cat > $lyx_test_qt_pro << EOF1
+qtHaveModule(core):		QT += core
+qtHaveModule(core5compat):	QT += core5compat
+percent.target = %
+percent.commands = @echo -n "\$(\$(@))\ "
+QMAKE_EXTRA_TARGETS += percent
+EOF1
+	    qmake $lyx_test_qt_pro -o $lyx_test_qt_mak 1>/dev/null 2>&1
+	    QT_CORE_INCLUDES=`cd $lyx_test_qt_dir; make -s -f $lyx_test_qt_mak INCPATH | sed 's/-I\. //g'`
+	    qt_corelibs=`cd $lyx_test_qt_dir; make -s -f $lyx_test_qt_mak LIBS`
+	    QT_CORE_LDFLAGS=`echo $qt_corelibs | tr ' ' '\n' | grep -e "^-L" | tr '\n' ' '`
+	    if test -z "$QT_CORE_LDFLAGS"; then
+		QT_CORE_LDFLAGS="-L`qmake -query QT_INSTALL_LIBS`"
+		QT_CORE_LIB="$qt_corelibs"
+	    else
+		QT_CORE_LIB=`echo $qt_corelibs | tr ' ' '\n' | grep -e "^-l" | tr '\n' ' '`
+	    fi
+	    if test -z "$QT_CORE_LIB"; then
+		AC_MSG_RESULT(no)
+	    else
+		AC_SUBST(QT_CORE_INCLUDES)
+		AC_SUBST(QT_CORE_LDFLAGS)
+		AC_SUBST(QT_CORE_LIB)
+		cat > $lyx_test_qt_pro << EOF2
+qtHaveModule(core):		QT += core
+qtHaveModule(core5compat):	QT += core5compat
+qtHaveModule(concurrent):	QT += concurrent
+qtHaveModule(gui):		QT += gui
+qtHaveModule(svg):		QT += svg
+qtHaveModule(widgets):		QT += widgets
+percent.target = %
+percent.commands = @echo -n "\$(\$(@))\ "
+QMAKE_EXTRA_TARGETS += percent
+EOF2
+		qmake $lyx_test_qt_pro -o $lyx_test_qt_mak 1>/dev/null 2>&1
+		QT_INCLUDES=`cd $lyx_test_qt_dir; make -s -f $lyx_test_qt_mak INCPATH | sed 's/-I\. //g'`
+		qt_guilibs=`cd $lyx_test_qt_dir; make -s -f $lyx_test_qt_mak LIBS`
+		QT_LDFLAGS=`echo $qt_guilibs | tr ' ' '\n' | grep -e "^-L" | tr '\n' ' '`
+		if test -z "$QT_LDFLAGS"; then
+		    QT_LDFLAGS="-L`qmake -query QT_INSTALL_LIBS`"
+		    QT_LIB="$qt_guilibs"
+		else
+		    QT_LIB=`echo $qt_guilibs | tr ' ' '\n' | grep -e "^-l" | tr '\n' ' '`
+		fi
+		QTLIB_VERSION=`qmake -v | grep "Qt version" | sed -e 's/.*\([[0-9]]\.[[0-9]]*\.[[0-9]]\).*/\1/'`
+		if test -z "$QT_LIB"; then
+		    AC_MSG_RESULT(no)
+		else
+		    AC_MSG_RESULT(yes)
+		    AC_SUBST(QT_INCLUDES)
+		    AC_SUBST(QT_LDFLAGS)
+		    AC_SUBST(QT_LIB)
+		    AC_SUBST(QTLIB_VERSION)
+		fi
+	    fi
+	    rm $lyx_test_qt_pro $lyx_test_qt_mak $lyx_test_qt_dir/.qmake.stash
+	    rmdir $lyx_test_qt_dir
+	else
+	    AC_MSG_RESULT(no)
+	fi
+])

configure.ac

@@ -13,7 +13,10 @@ AC_CONFIG_AUX_DIR(config)
 # First check the version
 LYX_CHECK_VERSION
 LYX_VERSION_SUFFIX
+LYX_CHECK_QT6
+if test x$USE_QT6 = xno ; then
 LYX_CHECK_QT5
+fi
 # Check how the files should be packaged
 AC_CANONICAL_TARGET
 LYX_USE_PACKAGING

src/frontends/qt/CategorizedCombo.cpp

@@ -34,6 +34,9 @@
 #include <QSortFilterProxyModel>
 #include <QStandardItemModel>
 #include <QTextFrame>
+#if QT_VERSION >= 0x060000
+#include <QtCore5Compat/QRegExp>
+#endif
 
 using namespace lyx::support;
 
@@ -270,7 +273,11 @@ QString CCItemDelegate::underlineFilter(QString const & s) const
 	if (f.isEmpty())
 		return s;
 	QString r(s);
+#if QT_VERSION < 0x060000
 	QRegExp pattern(charFilterRegExpC(f));
+#else
+	QRegularExpression pattern(charFilterRegExpC(f));
+#endif
 	r.replace(pattern, "<u><b>\\1</b></u>");
 	return r;
 }
@@ -287,7 +294,11 @@ void CategorizedCombo::Private::setFilter(QString const & s)
 		lastSel_ = filterModel_->mapToSource(filterModel_->index(sel, 0)).row();
 
 	filter_ = s;
+#if QT_VERSION < 0x060000
 	filterModel_->setFilterRegExp(charFilterRegExp(filter_));
+#else
+	filterModel_->setFilterRegularExpression(charFilterRegExp(filter_));
+#endif
 	countCategories();
 
 	// restore old selection

src/frontends/qt/GuiAbout.cpp

@@ -59,7 +59,9 @@ static QString credits()
 			out << qt_("Please install correctly to estimate the great\namount of work other people have done for the LyX project.");
 		} else {
 			QTextStream ts(&file);
+#if QT_VERSION < 0x060000
 			ts.setCodec("UTF-8");
+#endif
 			QString line;
 			do {
 				line = ts.readLine();
@@ -101,7 +103,9 @@ static QString release_notes()
 			out << qt_("Please install correctly to see what has changed\nfor this version of LyX.");
 		} else {
 			QTextStream ts(&file);
+#if QT_VERSION < 0x060000
 			ts.setCodec("UTF-8");
+#endif
 			QString line;
 			bool incomment = false;
 			bool inlist = false;
@@ -123,8 +127,13 @@ static QString release_notes()
 					continue;
 
 				// detect links to the tracker
+#if QT_VERSION < 0x060000
 				line.replace(QRegExp("(bug )(\\#)(\\d+)*"),
 					     "<a href=\"http://www.lyx.org/trac/ticket/\\3\">\\1\\3</a>");
+#else
+				line.replace(QRegularExpression("(bug )(\\#)(\\d+)*"),
+					     "<a href=\"http://www.lyx.org/trac/ticket/\\3\">\\1\\3</a>");
+#endif
 
 				// headings
 				if (line.startsWith("!!!")) {

src/frontends/qt/GuiApplication.cpp

@@ -89,7 +89,9 @@
 #include <QByteArray>
 #include <QBitmap>
 #include <QDateTime>
+#if QT_VERSION < 0x060000
 #include <QDesktopWidget>
+#endif
 #include <QEvent>
 #include <QFileOpenEvent>
 #include <QFileInfo>
@@ -135,6 +137,7 @@
 
 #if (QT_VERSION < 0x050000) || (QT_VERSION >= 0x050400)
 #if defined(Q_OS_WIN) || defined(Q_CYGWIN_WIN)
+#if (QT_VERSION < 0x060000)
 #if (QT_VERSION < 0x050000)
 #include <QWindowsMime>
 #define QWINDOWSMIME QWindowsMime
@@ -142,6 +145,7 @@
 #include <QWinMime>
 #define QWINDOWSMIME QWinMime
 #endif
+#endif
 #ifdef Q_CC_GNU
 #include <wtypes.h>
 #endif
@@ -808,7 +812,7 @@ public:
 ////////////////////////////////////////////////////////////////////////
 // Windows specific stuff goes here...
 
-#if (QT_VERSION < 0x050000) || (QT_VERSION >= 0x050400)
+#if (QT_VERSION < 0x050000) || (QT_VERSION >= 0x050400 && QT_VERSION < 0x060000)
 #if defined(Q_OS_WIN) || defined(Q_CYGWIN_WIN)
 // QWindowsMimeMetafile can only be compiled on Windows.
 
@@ -974,7 +978,7 @@ struct GuiApplication::Private
 		, last_state_(Qt::ApplicationInactive)
 	#endif
 	{
-	#if (QT_VERSION < 0x050000) || (QT_VERSION >= 0x050400)
+	#if (QT_VERSION < 0x050000) || (QT_VERSION >= 0x050400 && QT_VERSION < 0x060000)
 	#if defined(Q_OS_WIN) || defined(Q_CYGWIN_WIN)
 		/// WMF Mime handler for Windows clipboard.
 		wmf_mime_ = new QWindowsMimeMetafile;
@@ -1049,7 +1053,7 @@ struct GuiApplication::Private
 	QMacPasteboardMimeGraphics mac_pasteboard_mime_;
 #endif
 
-#if (QT_VERSION < 0x050000) || (QT_VERSION >= 0x050400)
+#if (QT_VERSION < 0x050000) || (QT_VERSION >= 0x050400 && QT_VERSION < 0x060000)
 #if defined(Q_OS_WIN) || defined(Q_CYGWIN_WIN)
 	/// WMF Mime handler for Windows clipboard.
 	QWindowsMimeMetafile * wmf_mime_;
@@ -1080,7 +1084,7 @@ GuiApplication::GuiApplication(int & argc, char ** argv)
 	QCoreApplication::setOrganizationName(app_name);
 	QCoreApplication::setOrganizationDomain("lyx.org");
 	QCoreApplication::setApplicationName(lyx_package);
-#if QT_VERSION >= 0x050000
+#if QT_VERSION >= 0x050000 && QT_VERSION < 0x060000
 	QCoreApplication::setAttribute(Qt::AA_UseHighDpiPixmaps);
 #endif
 
@@ -2567,6 +2571,7 @@ void GuiApplication::createView(QString const & geometry_arg, bool autoShow,
 		int x, y;
 		int w, h;
 		QChar sx, sy;
+#if QT_VERSION < 0x060000
 		QRegExp re( "[=]*(?:([0-9]+)[xX]([0-9]+)){0,1}[ ]*(?:([+-][0-9]*)){0,1}(?:([+-][0-9]*)){0,1}" );
 		re.indexIn(geometry_arg);
 		w = re.cap(1).toInt();
@@ -2575,6 +2580,16 @@ void GuiApplication::createView(QString const & geometry_arg, bool autoShow,
 		y = re.cap(4).toInt();
 		sx = re.cap(3).isEmpty() ? '+' : re.cap(3).at(0);
 		sy = re.cap(4).isEmpty() ? '+' : re.cap(4).at(0);
+#else
+		QRegularExpression re( "[=]*(?:([0-9]+)[xX]([0-9]+)){0,1}[ ]*(?:([+-][0-9]*)){0,1}(?:([+-][0-9]*)){0,1}" );
+		QRegularExpressionMatch match = re.match(geometry_arg);
+		w = match.captured(1).toInt();
+		h = match.captured(2).toInt();
+		x = match.captured(3).toInt();
+		y = match.captured(4).toInt();
+		sx = match.captured(3).isEmpty() ? '+' : match.captured(3).at(0);
+		sy = match.captured(4).isEmpty() ? '+' : match.captured(4).at(0);
+#endif
 		// Set initial geometry such that we can get the frame size.
 		view->setGeometry(x, y, w, h);
 		int framewidth = view->geometry().x() - view->x();
@@ -2582,7 +2597,11 @@ void GuiApplication::createView(QString const & geometry_arg, bool autoShow,
 		// Negative displacements must be interpreted as distances
 		// from the right or bottom screen borders.
 		if (sx == '-' || sy == '-') {
+#if QT_VERSION < 0x060000
 			QRect rec = QApplication::desktop()->screenGeometry();
+#else
+			QRect rec = QGuiApplication::primaryScreen()->geometry();
+#endif
 			if (sx == '-')
 				x += rec.width() - w - framewidth;
 			if (sy == '-')

src/frontends/qt/GuiClipboard.cpp

@@ -361,7 +361,11 @@ QString tidyHtml(QString const & input)
 	// clutter.
 	QTextDocument converter;
 	converter.setHtml(input);
+#if QT_VERSION < 0x060000
 	return converter.toHtml("utf-8");
+#else
+	return converter.toHtml();
+#endif
 }
 } // namespace
 

src/frontends/qt/GuiCommandBuffer.cpp

@@ -123,9 +123,17 @@ GuiCommandBuffer::GuiCommandBuffer(GuiView * view)
 	layout->addWidget(upPB, 0);
 	layout->addWidget(downPB, 0);
 	layout->addWidget(edit_, 10);
+#if QT_VERSION < 0x060000
 	layout->setMargin(0);
+#else
+	layout->setContentsMargins(0, 0, 0, 0);
+#endif
 	top->addLayout(layout);
+#if QT_VERSION < 0x060000
 	top->setMargin(0);
+#else
+	top->setContentsMargins(0, 0, 0, 0);
+#endif
 	setFocusProxy(edit_);
 
 	LastCommandsSection::LastCommands last_commands

src/frontends/qt/GuiFontLoader.cpp

@@ -29,6 +29,8 @@
 #include "support/Package.h"
 #include "support/os.h"
 
+#include "GuiApplication.h"
+
 #include <QFontInfo>
 #include <QFontDatabase>
 
@@ -207,14 +209,16 @@ QFont symbolFont(QString const & family, bool * ok)
 	upper[0] = family[0].toUpper();
 
 	QFont font;
-#if defined Q_WS_X11 || defined(QPA_XCB)
+	if (guiApp->platformName() == "qt4x11"
-	// On *nix we have to also specify the foundry to be able to
+	    || guiApp->platformName() == "xcb"
-	// discriminate our fonts when the texlive fonts are managed by
+	    || guiApp->platformName().contains("wayland")) {
-	// fontconfig. Unfortunately, doing the same on Windows breaks things.
+		// On *nix we have to also specify the foundry to be able to
-	font.setFamily(family + QLatin1String(" [LyEd]"));
+		// discriminate our fonts when the texlive fonts are managed by
-#else
+		// fontconfig. Unfortunately, doing the same on Windows breaks things.
-	font.setFamily(family);
+		font.setFamily(family + QLatin1String(" [LyEd]"));
-#endif
+	} else {
+		font.setFamily(family);
+	}
 	font.setStyleStrategy(QFont::NoFontMerging);
 #if QT_VERSION >= 0x040800
 	font.setStyleName("LyX");

src/frontends/qt/GuiListings.cpp

@@ -30,7 +30,11 @@
 #include <QLineEdit>
 #include <QPushButton>
 #include <QValidator>
+#if QT_VERSION < 0x060000
 #include <QRegExpValidator>
+#else
+#include <QRegularExpressionValidator>
+#endif
 
 using namespace std;
 using namespace lyx::support;
@@ -232,7 +236,11 @@ GuiListings::GuiListings(GuiView & lv)
 	numberStepLE->setValidator(new QIntValidator(0, 1000000, this));
 	firstlineLE->setValidator(new QIntValidator(0, 1000000, this));
 	lastlineLE->setValidator(new QIntValidator(0, 1000000, this));
+#if QT_VERSION < 0x060000
 	placementLE->setValidator(new QRegExpValidator(QRegExp("[\\*tbph]*"), this));
+#else
+	placementLE->setValidator(new QRegularExpressionValidator(QRegularExpression("[\\*tbph]*"), this));
+#endif
 
 	bc().setPolicy(ButtonPolicy::NoRepeatedApplyReadOnlyPolicy);
 	bc().setOK(buttonBox->button(QDialogButtonBox::Ok));

src/frontends/qt/GuiLog.cpp

@@ -41,12 +41,21 @@ namespace frontend {
 // Regular expressions needed at several places
 // FIXME: These regexes are incomplete. It would be good if we could collect those used in LaTeX::scanLogFile
 //        and LaTeX::scanBlgFile and re-use them here!(spitz, 2013-05-27)
+#if QT_VERSION < 0x060000
 // Information
 QRegExp exprInfo("^(Document Class:|LaTeX Font Info:|File:|Package:|Language:|.*> INFO - |\\(|\\\\).*$");
 // Warnings
 QRegExp exprWarning("^(## Warning|LaTeX Warning|LaTeX Font Warning|Package [\\w\\.]+ Warning|Class \\w+ Warning|Warning--|Underfull|Overfull|.*> WARN - ).*$");
 // Errors
 QRegExp exprError("^(ERROR: |!|.*---line [0-9]+ of file|.*> FATAL - |.*> ERROR - |Missing character: There is no ).*$");
+#else
+// Information
+QRegularExpression exprInfo("^(Document Class:|LaTeX Font Info:|File:|Package:|Language:|.*> INFO - |\\(|\\\\).*$");
+// Warnings
+QRegularExpression exprWarning("^(## Warning|LaTeX Warning|LaTeX Font Warning|Package [\\w\\.]+ Warning|Class \\w+ Warning|Warning--|Underfull|Overfull|.*> WARN - ).*$");
+// Errors
+QRegularExpression exprError("^(ERROR: |!|.*---line [0-9]+ of file|.*> FATAL - |.*> ERROR - |Missing character: There is no ).*$");
+#endif
 
 
 /////////////////////////////////////////////////////////////////////
@@ -82,6 +91,7 @@ LogHighlighter::LogHighlighter(QTextDocument * parent)
 
 void LogHighlighter::highlightBlock(QString const & text)
 {
+#if QT_VERSION < 0x060000
 	// Info
 	int index = exprInfo.indexIn(text);
 	while (index >= 0) {
@@ -103,6 +113,35 @@ void LogHighlighter::highlightBlock(QString const & text)
 		setFormat(index, length, errorFormat);
 		index = exprError.indexIn(text, index + length);
 	}
+#else
+	// Info
+	QRegularExpressionMatch match = exprInfo.match(text);
+	int index = match.capturedStart(1);
+	while (index >= 0) {
+		int length = match.capturedEnd(1) - index;
+		setFormat(index, length, infoFormat);
+		match = exprInfo.match(text, index + length);
+		index = match.capturedStart(1);
+	}
+	// LaTeX Warning:
+	match = exprWarning.match(text);
+	index = match.capturedStart(1);
+	while (index >= 0) {
+		int length = match.capturedEnd(1) - index;
+		setFormat(index, length, warningFormat);
+		match = exprWarning.match(text, index + length);
+		index = match.capturedStart(1);
+	}
+	// ! error
+	match = exprError.match(text);
+	index = match.capturedStart(1);
+	while (index >= 0) {
+		int length = match.capturedEnd(1) - index;
+		setFormat(index, length, errorFormat);
+		match = exprError.match(text, index + length);
+		index = match.capturedStart(1);
+	}
+#endif
 }
 
 
@@ -195,7 +234,11 @@ void GuiLog::on_openDirPB_clicked()
 }
 
 
+#if QT_VERSION < 0x060000
 void GuiLog::goTo(QRegExp const & exp) const
+#else
+void GuiLog::goTo(QRegularExpression const & exp) const
+#endif
 {
 	QTextCursor const newc =
 		logTB->document()->find(exp, logTB->textCursor());
@@ -203,7 +246,11 @@ void GuiLog::goTo(QRegExp const & exp) const
 }
 
 
+#if QT_VERSION < 0x060000
 bool GuiLog::contains(QRegExp const & exp) const
+#else
+bool GuiLog::contains(QRegularExpression const & exp) const
+#endif
 {
 	return !logTB->document()->find(exp, logTB->textCursor()).isNull();
 }

src/frontends/qt/GuiLog.h

@@ -66,10 +66,17 @@ private:
 	docstring title() const;
 	/// put the log file into the ostream
 	void getContents(std::ostream & ss) const;
+#if QT_VERSION < 0x060000
 	/// go to the next occurrence of the RegExp
 	void goTo(QRegExp const & exp) const;
 	/// does the document after cursor position contain the RegExp?
 	bool contains(QRegExp const & exp) const;
+#else
+	/// go to the next occurrence of the RegExp
+	void goTo(QRegularExpression const & exp) const;
+	/// does the document after cursor position contain the RegExp?
+	bool contains(QRegularExpression const & exp) const;
+#endif
 
 private:
 	/// Recognized log file-types

src/frontends/qt/GuiPrefs.cpp

@@ -188,7 +188,11 @@ QString browseRelToSub(QString const & filename, QString const & relpath,
 		toqstr(makeRelPath(qstring_to_ucs4(outname), qstring_to_ucs4(relpath)));
 
 	QString testname = reloutname;
+#if QT_VERSION < 0x060000
 	testname.remove(QRegExp("^(\\.\\./)+"));
+#else
+	testname.remove(QRegularExpression("^(\\.\\./)+"));
+#endif
 
 	if (testname.contains("/"))
 		return outname;
@@ -2424,7 +2428,11 @@ PrefLanguage::PrefLanguage(GuiPreferences * form)
 	startCommandED->setValidator(new NoNewLineValidator(startCommandED));
 	endCommandED->setValidator(new NoNewLineValidator(endCommandED));
 
+#if QT_VERSION < 0x060000
 	defaultDecimalSepED->setValidator(new QRegExpValidator(QRegExp("\\S"), this));
+#else
+	defaultDecimalSepED->setValidator(new QRegularExpressionValidator(QRegularExpression("\\S"), this));
+#endif
 	defaultDecimalSepED->setMaxLength(1);
 
 	defaultLengthUnitCO->addItem(lyx::qt_(unit_name_gui[Length::CM]), Length::CM);
@@ -2584,9 +2592,12 @@ PrefUserInterface::PrefUserInterface(GuiPreferences * form)
 	iconSetCO->addItem(qt_("Classic"), "classic");
 	iconSetCO->addItem(qt_("Oxygen"), "oxygen");
 
-#if (!(defined Q_WS_X11 || defined(QPA_XCB)) || QT_VERSION < 0x040600)
+#if QT_VERSION >= 0x040600
-	useSystemThemeIconsCB->hide();
+	if (guiApp->platformName() != "qt4x11"
+	    && guiApp->platformName() != "xcb"
+	    && !guiApp->platformName().contains("wayland"))
 #endif
+		useSystemThemeIconsCB->hide();
 }
 
 

src/frontends/qt/GuiTabular.cpp

@@ -176,7 +176,11 @@ GuiTabular::GuiTabular(QWidget * parent)
 	connect(tabularWidthED, SIGNAL(textEdited(const QString &)),
 		this, SLOT(checkEnabled()));
 
+#if QT_VERSION < 0x060000
 	decimalPointED->setValidator(new QRegExpValidator(QRegExp("\\S"), this));
+#else
+	decimalPointED->setValidator(new QRegularExpressionValidator(QRegularExpression("\\S"), this));
+#endif
 	decimalPointED->setMaxLength(1);
 
 	// initialize the length validator

src/frontends/qt/GuiThesaurus.cpp

@@ -124,9 +124,14 @@ void GuiThesaurus::selectionChanged()
 	QString item = meaningsTV->currentItem()->text(col);
 	// cut out the classification in brackets:
 	// "hominid (generic term)" -> "hominid"
+#if QT_VERSION < 0x060000
 	QRegExp re("^([^\\(\\)]+)\\b\\(?.*\\)?.*$");
+#else
+	QRegularExpression re("^([^\\(\\)]+)\\b\\(?.*\\)?.*$");
+#endif
 	// This is for items with classifications at the beginning:
 	// "(noun) man" -> "man"; "(noun) male (generic term)" -> "male"
+#if QT_VERSION < 0x060000
 	QRegExp rex("^(\\(.+\\))\\s*([^\\(\\)]+)\\s*\\(?.*\\)?.*$");
 	int pos = re.indexIn(item);
 	if (pos > -1)
@@ -134,6 +139,15 @@ void GuiThesaurus::selectionChanged()
 	pos = rex.indexIn(item);
 	if (pos > -1)
 		item = rex.cap(2).trimmed();
+#else
+	QRegularExpression rex("^(\\(.+\\))\\s*([^\\(\\)]+)\\s*\\(?.*\\)?.*$");
+	QRegularExpressionMatch match = re.match(item);
+	if (match.hasMatch())
+		item = match.captured(1).trimmed();
+	match = rex.match(item);
+	if (match.hasMatch())
+		item = match.captured(2).trimmed();
+#endif
 	replaceED->setText(item);
 	replacePB->setEnabled(!isBufferReadonly());
 	changed();
@@ -151,9 +165,14 @@ void GuiThesaurus::selectionClicked(QTreeWidgetItem * item, int col)
 	QString str = item->text(col);
 	// cut out the classification in brackets:
 	// "hominid (generic term)" -> "hominid"
+#if QT_VERSION < 0x060000
 	QRegExp re("^([^\\(\\)]+)\\b\\(?.*\\)?.*$");
+#else
+	QRegularExpression re("^([^\\(\\)]+)\\b\\(?.*\\)?.*$");
+#endif
 	// This is for items with classifications at the beginning:
 	// "(noun) man" -> "man"; "(noun) male (generic term)" -> "male"
+#if QT_VERSION < 0x060000
 	QRegExp rex("^(\\(.+\\))\\s*([^\\(\\)]+)\\s*\\(?.*\\)?.*$");
 	int pos = re.indexIn(str);
 	if (pos > -1)
@@ -161,6 +180,15 @@ void GuiThesaurus::selectionClicked(QTreeWidgetItem * item, int col)
 	pos = rex.indexIn(str);
 	if (pos > -1)
 		str = rex.cap(2).trimmed();
+#else
+	QRegularExpression rex("^(\\(.+\\))\\s*([^\\(\\)]+)\\s*\\(?.*\\)?.*$");
+	QRegularExpressionMatch match = re.match(str);
+	if (match.hasMatch())
+		str = match.captured(1).trimmed();
+	match = rex.match(str);
+	if (match.hasMatch())
+		str = match.captured(2).trimmed();
+#endif
 	entryCO->insertItem(0, str);
 	entryCO->setCurrentIndex(0);
 

src/frontends/qt/GuiView.cpp

@@ -655,7 +655,7 @@ GuiView::GuiView(int id)
 	zoom_in_->setFlat(true);
 	zoom_in_->setFixedSize(QSize(fm.height(), fm.height()));
 	zoom_out_ = new QPushButton(statusBar());
-	zoom_out_->setText(QString(0x2212));
+	zoom_out_->setText(QString(QChar(0x2212)));
 	zoom_out_->setFixedSize(QSize(fm.height(), fm.height()));
 	zoom_out_->setFlat(true);
 

src/frontends/qt/IconPalette.cpp

@@ -19,7 +19,9 @@
 #include <QToolTip>
 #include <QToolBar>
 #include <QApplication>
+#if QT_VERSION < 0x060000
 #include <QDesktopWidget>
+#endif
 #include <QPainter>
 #include <QStyle>
 #include <QStyleOptionFrame>
@@ -76,7 +78,9 @@ void TearOff::paintEvent(QPaintEvent * /*event*/)
 	menuOpt.checkType = QStyleOptionMenuItem::NotCheckable;
 	menuOpt.menuRect = rect();
 	menuOpt.maxIconWidth = 0;
+#if QT_VERSION < 0x060000
 	menuOpt.tabWidth = 0;
+#endif
 	menuOpt.menuItemType = QStyleOptionMenuItem::TearOff;
 	menuOpt.rect.setRect(fw, fw, width() - (fw * 2),
 		style()->pixelMetric(QStyle::PM_MenuTearoffHeight, 0, this));
@@ -92,12 +96,20 @@ IconPalette::IconPalette(QWidget * parent)
 	: QWidget(parent, Qt::Popup), tornoff_(false)
 {
 	QVBoxLayout * v = new QVBoxLayout(this);
+#if QT_VERSION < 0x060000
 	v->setMargin(0);
+#else
+	v->setContentsMargins(0, 0, 0, 0);
+#endif
 	v->setSpacing(0);
 	layout_ = new QGridLayout;
 	layout_->setSpacing(0);
 	const int fw = style()->pixelMetric(QStyle::PM_MenuPanelWidth, 0, this);
+#if QT_VERSION < 0x060000
 	layout_->setMargin(fw);
+#else
+	layout_->setContentsMargins(0, 0, 0, 0);
+#endif
 	tearoffwidget_ = new TearOff(this);
 	connect(tearoffwidget_, SIGNAL(tearOff()), this, SLOT(tearOff()));
 	v->addWidget(tearoffwidget_);
@@ -166,7 +178,11 @@ void IconPalette::showEvent(QShowEvent * /*event*/)
 		voffset -= parheight;
 	}
 
+#if QT_VERSION < 0x060000
 	QRect const screen = qApp->desktop()->availableGeometry(this);
+#else
+	QRect const screen = qApp->primaryScreen()->availableGeometry();
+#endif
 	QPoint const gpos = parentWidget()->mapToGlobal(
 		parentWidget()->geometry().bottomLeft());
 

src/frontends/qt/IconPalette.h

@@ -27,7 +27,11 @@ class TearOff : public QWidget {
 	Q_OBJECT
 public:
 	TearOff(QWidget * parent);
+#if QT_VERSION < 0x060000
 	void enterEvent(QEvent *) override;
+#else
+	void enterEvent(QEvent *);
+#endif
 	void leaveEvent(QEvent *) override;
 	void mouseReleaseEvent (QMouseEvent *) override;
 Q_SIGNALS:

src/frontends/qt/LaTeXHighlighter.cpp

@@ -43,6 +43,7 @@ LaTeXHighlighter::LaTeXHighlighter(QTextDocument * parent, bool at_letter)
 
 void LaTeXHighlighter::highlightBlock(QString const & text)
 {
+#if QT_VERSION < 0x060000
 	// $ $
 	static const QRegExp exprMath("\\$[^\\$]*\\$");
 	int index = exprMath.indexIn(text);
@@ -127,6 +128,102 @@ void LaTeXHighlighter::highlightBlock(QString const & text)
 		setFormat(index, length, warningFormat);
 		index = exprWarning.indexIn(text, index + length);
 	}
+#else
+	// $ $
+	static const QRegularExpression exprMath("\\$[^\\$]*\\$");
+	QRegularExpressionMatch match = exprMath.match(text);
+	int index = match.capturedStart(1);
+	while (index >= 0) {
+		int length = match.capturedEnd(1) - index;
+		setFormat(index, length, mathFormat);
+		match = exprMath.match(text, index + length);
+		int index = match.capturedStart(1);
+	}
+	// [ ]
+	static const QRegularExpression exprStartDispMath("(\\\\\\[|"
+		"\\\\begin\\{equation\\**\\}|"
+		"\\\\begin\\{eqnarray\\**\\}|"
+		"\\\\begin\\{align(ed|at)*\\**\\}|"
+		"\\\\begin\\{flalign\\**\\}|"
+		"\\\\begin\\{gather\\**\\}|"
+		"\\\\begin\\{multline\\**\\}|"
+		"\\\\begin\\{array\\**\\}|"
+		"\\\\begin\\{cases\\**\\}"
+		")");
+	static const QRegularExpression exprEndDispMath("(\\\\\\]|"
+		"\\\\end\\{equation\\**\\}|"
+		"\\\\end\\{eqnarray\\**\\}|"
+		"\\\\end\\{align(ed|at)*\\**\\}|"
+		"\\\\end\\{flalign\\**\\}|"
+		"\\\\end\\{gather\\**\\}|"
+		"\\\\end\\{multline\\**\\}|"
+		"\\\\end\\{array\\**\\}|"
+		"\\\\end\\{cases\\**\\}"
+		")");
+	int startIndex = 0;
+	// if previous block was in 'disp math'
+	// start search from 0 (for end disp math)
+	// otherwise, start search from 'begin disp math'
+	if (previousBlockState() != 1) {
+		match = exprStartDispMath.match(text);
+		startIndex = match.capturedStart(1);
+	}
+	while (startIndex >= 0) {
+		match = exprEndDispMath.match(text, startIndex);
+		int endIndex = match.capturedStart(1);
+		int length;
+		if (endIndex == -1) {
+			setCurrentBlockState(1);
+			length = text.length() - startIndex;
+		} else {
+			length = match.capturedEnd(1) - startIndex;
+		}
+		setFormat(startIndex, length, mathFormat);
+		match = exprStartDispMath.match(text, startIndex + length);
+		startIndex = match.capturedStart(1);
+	}
+	// \whatever
+	static const QRegularExpression exprKeywordAtOther("\\\\[A-Za-z]+");
+	// \wh@tever
+	static const QRegularExpression exprKeywordAtLetter("\\\\[A-Za-z@]+");
+	QRegularExpression const & exprKeyword = at_letter_
+			? exprKeywordAtLetter : exprKeywordAtOther;
+	match = exprKeyword.match(text);
+	index = match.capturedStart(1);
+	while (index >= 0) {
+		int length = match.capturedEnd(1) - index;
+		setFormat(index, length, keywordFormat);
+		match = exprKeyword.match(text, index + length);
+		index = match.capturedStart(1);
+	}
+	// %comment
+	// Treat a line as a comment starting at a percent sign
+	// * that is the first character in a line
+	// * that is preceded by
+	// ** an even number of backslashes
+	// ** any character other than a backslash
+	QRegularExpression exprComment("(?:^|[^\\\\])(?:\\\\\\\\)*(%).*$");
+	match = exprComment.match(text);
+	index = match.capturedStart(1);
+	while (index >= 0) {
+		int const length = match.capturedEnd(1) - index
+				 - (index - match.capturedStart(0));
+		setFormat(index, length, commentFormat);
+		match = exprComment.match(text, index + length);
+		index = match.capturedStart(1);
+	}
+	// <LyX Warning: ...>
+	QString lyxwarn = qt_("LyX Warning: ");
+	QRegularExpression exprWarning("<" + lyxwarn + "[^<]*>");
+	match = exprWarning.match(text);
+	index = match.capturedStart(1);
+	while (index >= 0) {
+		int length = match.capturedEnd(1) - index;
+		setFormat(index, length, warningFormat);
+		match = exprWarning.match(text, index + length);
+		index = match.capturedStart(1);
+	}
+#endif
 }
 
 } // namespace frontend

src/frontends/qt/LayoutBox.cpp

@@ -300,7 +300,11 @@ QString LayoutItemDelegate::underlineFilter(QString const & s) const
 	if (f.isEmpty())
 		return s;
 	QString r(s);
+#if QT_VERSION < 0x060000
 	QRegExp pattern(charFilterRegExpC(f));
+#else
+	QRegularExpression pattern(charFilterRegExpC(f));
+#endif
 	r.replace(pattern, "<u><b>\\1</b></u>");
 	return r;
 }
@@ -321,7 +325,11 @@ void LayoutBox::Private::setFilter(QString const & s)
 		lastSel_ = filterModel_->mapToSource(filterModel_->index(sel, 0)).row();
 
 	filter_ = s;
+#if QT_VERSION < 0x060000
 	filterModel_->setFilterRegExp(charFilterRegExp(filter_));
+#else
+	filterModel_->setFilterRegularExpression(charFilterRegExp(filter_));
+#endif
 	countCategories();
 
 	// restore old selection

src/frontends/qt/Validator.cpp

@@ -182,7 +182,11 @@ NoNewLineValidator::NoNewLineValidator(QWidget * parent)
 
 QValidator::State NoNewLineValidator::validate(QString & qtext, int &) const
 {
+#if QT_VERSION < 0x060000
 	qtext.remove(QRegExp("[\\n\\r]"));
+#else
+	qtext.remove(QRegularExpression("[\\n\\r]"));
+#endif
 	return QValidator::Acceptable;
 }
 

src/support/mutex.cpp

@@ -20,12 +20,20 @@ namespace lyx {
 
 struct Mutex::Private
 {
+#if QT_VERSION < 0x060000
 	// QMutex::Recursive: less risks for dead-locks
 	Private() : qmutex_(QMutex::Recursive)
 	{
 	}
 
 	QMutex qmutex_;
+#else
+	Private() : qmutex_()
+	{
+	}
+
+	QRecursiveMutex qmutex_;
+#endif
 };