build,qt: Allow building QGpgME for Qt 6

* configure.ac: Look for Qt 5 and/or Qt 6. Require C++17 if Qt 6 binding
is built. Build cmake files QGpgmeConfig* for Qt 5 and QGpgmeQt6Config*
for Qt 6.
(available_languages): Add "qt5" and "qt6".
(WANT_QT5, WANT_QT6): New conditionals.
* lang/qt/src/Makefile.am: Keep building libqgpgme for Qt 5. Build
libqgpgmeqt6 for Qt 6.
* lang/qt/tests/Makefile.am: Build tests for Qt 5 or Qt 6.
* lang/qt/src/QGpgmeQt6Config-w32.cmake.in.in,
lang/qt/src/QGpgmeQt6Config.cmake.in.in,
lang/qt/src/QGpgmeQt6ConfigVersion.cmake.in, m4/qt6.m4: New.
--

This makes it possible to build QGpgME optionally for Qt 6.4.0 or later.
By default or if the language "qt" is enabled, then QGpgME is built
either for Qt 5 (if found) or Qt 6. A build for Qt 5 or Qt 6 can be
requested by explicitly enabling the language "qt5" or "qt6". Building
QGpgME for Qt 5 and Qt 6 simultaneously is not supported.

1 files changed, 82 insertions, 0 deletions

diff --git a/m4/qt6.m4 b/m4/qt6.m4
new file mode 100644
index 00000000..6e864fb1
--- /dev/null
+++ b/m4/qt6.m4
@@ -0,0 +1,82 @@
+dnl qt6.m4
+dnl Copyright (C) 2016 Intevation GmbH
+dnl
+dnl This file is part of gpgme and is provided under the same license as gpgme
+
+dnl Autoconf macro to find Qt6
+dnl
+dnl sets GPGME_QT6_LIBS and GPGME_QT6_CFLAGS
+dnl
+dnl if QT6 was found have_qt6_libs is set to yes
+
+AC_DEFUN([FIND_QT6],
+[
+  have_qt6_libs="no";
+
+  PKG_CHECK_MODULES(GPGME_QT6,
+                    Qt6Core >= 6.4.0,
+                    [have_qt6_libs="yes"],
+                    [have_qt6_libs="no"])
+
+  PKG_CHECK_MODULES(GPGME_QT6TEST,
+                    Qt6Test >= 6.4.0,
+                    [have_qt6test_libs="yes"],
+                    [have_qt6test_libs="no"])
+
+  if ! test "$have_w32_system" = yes; then
+    if "$PKG_CONFIG" --variable qt_config Qt6Core | grep -q "reduce_relocations"; then
+      GPGME_QT6_CFLAGS="$GPGME_QT6_CFLAGS -fpic"
+    fi
+  fi
+  if test "$have_qt6_libs" = "yes"; then
+    # Qt6 moved moc to libexec
+    qt6libexecdir=$($PKG_CONFIG --variable=libexecdir 'Qt6Core >= 6.4.0')
+    AC_PATH_TOOL(MOC, moc, [], [$qt6libexecdir])
+    AC_MSG_CHECKING([moc version])
+    mocversion=`$MOC -v 2>&1`
+    mocversiongrep=`echo $mocversion | grep -E "Qt 6|moc 6"`
+    if test x"$mocversiongrep" != x"$mocversion"; then
+      AC_MSG_RESULT([no])
+      # moc was not the qt6 one, try with moc-qt6
+      AC_CHECK_TOOL(MOC2, moc-qt6)
+      mocversion=`$MOC2 -v 2>&1`
+      mocversiongrep=`echo $mocversion | grep -E "Qt 6|moc-qt6 6|moc 6"`
+      if test x"$mocversiongrep" != x"$mocversion"; then
+        AC_CHECK_TOOL(QTCHOOSER, qtchooser)
+        qt6tooldir=`QT_SELECT=qt6 qtchooser -print-env | grep QTTOOLDIR | cut -d '=' -f 2 | cut -d \" -f 2`
+        mocversion=`$qt6tooldir/moc -v 2>&1`
+        mocversiongrep=`echo $mocversion | grep -E "Qt 6|moc 6"`
+        if test x"$mocversiongrep" != x"$mocversion"; then
+          # no valid moc found
+          have_qt6_libs="no";
+        else
+          MOC=$qt6tooldir/moc
+        fi
+      else
+        MOC=$MOC2
+      fi
+    fi
+    AC_MSG_RESULT([$mocversion])
+    dnl Check that a binary can actually be build with this qt.
+    dnl pkg-config may be set up in a way that it looks also for libraries
+    dnl of the build system and not only for the host system. In that case
+    dnl we check here that we can actually compile / link a qt application
+    dnl for host.
+    OLDCPPFLAGS=$CPPFLAGS
+    CPPFLAGS=$GPGME_QT6_CFLAGS
+    OLDLIBS=$LIBS
+    LIBS=$GPGME_QT6_LIBS
+    AC_LANG_PUSH(C++)
+    AC_MSG_CHECKING([whether a simple qt program can be built])
+    AC_LINK_IFELSE([AC_LANG_SOURCE([
+    #include <QCoreApplication>
+    int main (int argc, char **argv) {
+    QCoreApplication app(argc, argv);
+    app.exec();
+    }])], [have_qt6_libs='yes'], [have_qt6_libs='no'])
+    AC_MSG_RESULT([$have_qt6_libs])
+    AC_LANG_POP()
+    CPPFLAGS=$OLDCPPFLAGS
+    LIBS=$OLDLIBS
+  fi
+])