autoconf: remove support for compiling against Qt4

Most of the changes consist in assuming that USE_QT5=yes.

Update INSTALL and README accordingly.

INSTALL

@@ -52,18 +52,17 @@ You will also probably need GNU m4 (perhaps installed as gm4).
 Requirements
 ------------
 
-First of all, you will need a C++11 standard conforming compiler, like gcc (at
-least 4.9) or clang.
+First of all, you will need a C++11 standard conforming compiler, like g++ (at
+least 4.9, to have proper srd::regex) or clang++.
 
 LyX makes great use of the C++ Standard Template Library (STL).
 This means that gcc users will have to install the relevant libstdc++
 library to be able to compile this version of LyX.
 
 For full LyX usability we suggest to use Qt 5.6 and higher, or at the
-very least Qt 5.4. For compilation you need to compile against at least
-Qt 4.8 which has been widely tested, and for Windows we advise at least
-Qt 4.8.4. The only special point to make is that you must ensure that
-both LyX and the Qt libraries are compiled with the same C++ compiler.
+very least Qt 5.4. It is also possible to compile against Qt 6.The
+only special point to make is that you must ensure that both LyX and
+the Qt libraries are compiled with the same C++ compiler.
 
 To build LyX with spell checking capabilities included you have to
 install at least one of the development packages of the spell checker
@@ -124,8 +123,8 @@ flags:
 
     The `gprof' build type compiles and links with -pg option with gcc.
 
-  o --disable-qt5 that forces configuration with Qt 4.x when Qt 5.x is
-    also available. By default Qt5 is tried first, and then Qt4.
+  o --enable-qt6 that checks configuration with Qt 6.x, and then Qt
+    5.x. By default, only Qt5 is tried.
 
   o --with-extra-lib=DIRECTORY that specifies the path where LyX will
     find extra libraries (like Qt) it needs. Defaults to NONE

README

@@ -91,8 +91,7 @@ What do I need to compile LyX from the source distribution?
       need at least gcc 4.9.
 
     * The Qt library, at least version 5.2 (5.6 recommended). It is
-      still possible to compile with Qt 4.8, but this is not
-      recommended.
+      also possible to compile with Qt 6.x.
 
     Read the file "INSTALL" for more information on compiling.
 

TODO.killqt4

@@ -1,10 +1,7 @@
 Things left to do after killing Qt4 (obtained by grepping for Qt4 and 'Qt 4'):
 * look at the FIXME KILLQT4 comments in src/ and resolve them
-* update README
-* update INSTALL
 * update INSTALL.cmake
 * update INSTALL.MacOSX
-* update autoconf
 * update cmake
 * check whether development/autotests/keytest.py really needs QT4
   investigate references to Qt4 in keytest

config/lyxinclude.m4

@@ -74,18 +74,6 @@ AC_MSG_RESULT([$USE_QT6])
 AC_SUBST([USE_QT6])
 ])
 dnl
-AC_DEFUN([LYX_CHECK_QT5],[
-AC_MSG_CHECKING([whether Qt5 is disabled])
-AC_ARG_ENABLE([qt5],
-  [AS_HELP_STRING([--disable-qt5],[do not use Qt5 for building])],
-  USE_QT5=$enableval, USE_QT5=yes)
-if test x$USE_QT5 != xno ; then
-  AC_MSG_RESULT([no])
-else
-  AC_MSG_RESULT([yes])
-fi
-AC_SUBST([USE_QT5])
-])
 
 
 dnl Usage: LYX_WARNING(message)  Displays the warning "message" and sets the
@@ -381,9 +369,8 @@ if test x$GXX = xyes; then
     AM_CXXFLAGS="$AM_CXXFLAGS -fno-omit-frame-pointer"
   fi
 
-  if test x$USE_QT5 = xyes -o x$USE_QT6 = xyes; then
   AS_CASE([$host], [*mingw*|*cygwin*], [], [AM_CXXFLAGS="-fPIC $AM_CXXFLAGS"])
-  fi
+
   dnl Warnings are for preprocessor too
   if test x$enable_warnings = xyes ; then
       AM_CPPFLAGS="$AM_CPPFLAGS -Wall -Wextra"

config/qt.m4

@@ -29,7 +29,7 @@ AC_DEFUN([QT_CHECK_COMPILE],
 		if test $USE_QT6 = "yes" ; then
 		    qt_corelibs="-lQt6Core -lQt6Core5Compat"
 		    qt_guilibs="-lQt6Core -lQt6Core5Compat -lQt6Concurrent -lQt6Gui -lQt6Svg -lQt6Widgets"
-		elif test $USE_QT5 = "yes" ; then
+		else
 		    qt_corelibs="-lQt5Core"
 		    qt_guilibs="-lQt5Core -lQt5Concurrent -lQt5Gui -lQt5Svg -lQt5Widgets"
 		fi
@@ -58,8 +58,6 @@ AC_DEFUN([QT_CHECK_COMPILE],
 	if test -z "$qt_cv_libname"; 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])
 			AC_MSG_ERROR([cannot compile a simple Qt executable. Check you have the right \$QTDIR.])
@@ -73,11 +71,9 @@ AC_DEFUN([QT_CHECK_COMPILE],
 AC_DEFUN([QT_FIND_TOOL],
 [
 	$1=
-	qt_major=4
+	qt_major=5
 	if test "x$USE_QT6" != "xno" ; then
 		qt_major=6
-	elif test "x$USE_QT5" != "xno" ; then
-		qt_major=5
 	fi
 	qt_ext="qt$qt_major"
 
@@ -191,23 +187,7 @@ AC_DEFUN([QT_DO_IT_ALL],
 	  dnl Try again with Qt5 and then Qt4 if configuring for Qt6/5 fails
 	  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
 		fi
@@ -246,25 +226,13 @@ AC_DEFUN([QT_DO_IT_ALL],
 	    [AC_MSG_RESULT(yes)
 	     AC_DEFINE(QPA_XCB, 1, [Define if Qt uses the X Window System])],
 	    [AC_MSG_RESULT(no)])
-	elif test x$USE_QT5 = xyes ; then
+	else
 	  AC_EGREP_CPP(xcb,
 	    [#include <$lyx_qt5_config>
 	    QT_QPA_DEFAULT_PLATFORM_NAME],
 	    [AC_MSG_RESULT(yes)
 	     AC_DEFINE(QPA_XCB, 1, [Define if Qt uses the X Window System])],
 	    [AC_MSG_RESULT(no)])
-	else
-	  AC_PREPROC_IFELSE([AC_LANG_SOURCE([
-	    [#include <qglobal.h>],
-	    [#ifndef Q_WS_X11],
-	    [#error Fail],
-	    [#endif]])],
-	    qt_use_x11=yes,
-	    qt_use_x11=no)
-	  AC_MSG_RESULT($qt_use_x11)
-	  if test "x$qt_use_x11" = "xyes"; then
-	    QT_LIB="$QT_LIB -lX11"
-	  fi
 	fi
 	CPPFLAGS=$save_CPPFLAGS
 
@@ -287,9 +255,6 @@ AC_DEFUN([QT_DO_PKG_CONFIG],
 	  PKG_CONFIG_PATH=$qt_cv_dir/lib:$qt_cv_dir/lib/pkgconfig:$PKG_CONFIG_PATH
 	  export PKG_CONFIG_PATH
 	fi
-	qt_corelibs="QtCore"
-	qt_guilibs="QtCore QtGui QtSvg"
-	if test "x$USE_QT5" != "xno" ; then
 	qt_corelibs="Qt5Core"
 	qt_guilibs="Qt5Core Qt5Concurrent Qt5Gui Qt5Svg Qt5Widgets"
 	lyx_use_x11extras=false
@@ -309,7 +274,6 @@ AC_DEFUN([QT_DO_PKG_CONFIG],
 	if $lyx_use_macextras; then
 		qt_guilibs="$qt_guilibs Qt5MacExtras"
 	fi
-	fi
 	PKG_CHECK_MODULES(QT_CORE, $qt_corelibs,,[:])
 	if test "$pkg_failed" = "no" ; then
 		QT_CORE_INCLUDES=$QT_CORE_CFLAGS

configure.ac

@@ -14,9 +14,6 @@ AC_CONFIG_AUX_DIR(config)
 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