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.

7 files changed, 541 insertions, 59 deletions

diff --git a/configure.ac b/configure.ac
index 8fcf14f6..cee1781d 100644
--- a/configure.ac
+++ b/configure.ac
@@ -218,7 +218,7 @@ have_w64_system=no
 have_macos_system=no
 build_w32_glib=no
 build_w32_qt=no
-available_languages="cl cpp python qt"
+available_languages="cl cpp python qt qt5 qt6"
 default_languages="cl cpp python qt"
 case "${host}" in
     x86_64-*mingw32*)
@@ -305,7 +305,9 @@ fi
 #       lang/Makefile.am's DIST_SUBDIRS.
 AC_ARG_ENABLE([languages],
               AS_HELP_STRING([--enable-languages=languages],
-                             [enable only specific language bindings]),
+                             [enable only specific language bindings:
+                              cl cpp python qt qt5 qt6 (qt selects qt5 or qt6,
+                              and qt5 and qt6 exclude each other)]),
                              [enabled_languages=`echo $enableval | \
                              tr ',:' '  ' | tr '[A-Z]' '[a-z]' | \
                              sed 's/c++/cpp/'`],
@@ -331,84 +333,160 @@ for language in $enabled_languages; do
     fi
 done
 
-# Enable C++ 11 if cpp language is requested
-LIST_MEMBER("cpp", $enabled_languages)
+# Check whether Qt5 and/or Qt6 are enabled explicitly
+want_qt5="no";
+LIST_MEMBER("qt5", $enabled_languages)
 if test "$found" = "1"; then
-    AX_CXX_COMPILE_STDCXX(11, noext, optional)
-    if test "$HAVE_CXX11" != "1"; then
-        if test "$explicit_languages" = "1"; then
-            AC_MSG_ERROR([[
+    want_qt5="yes";
+    # Remove qt5; further down qt will be added
+    enabled_languages=$(echo $enabled_languages | sed 's/qt5//')
+fi
+want_qt6="no";
+LIST_MEMBER("qt6", $enabled_languages)
+if test "$found" = "1"; then
+    want_qt6="yes";
+    # Remove qt6; further down qt will be added
+    enabled_languages=$(echo $enabled_languages | sed 's/qt6//')
+fi
+if test "$want_qt5" = "yes" -a "$want_qt6" = "yes"; then
+    AC_MSG_ERROR([[
 ***
-*** A compiler with c++11 support is required for the c++ binding.
+*** The bindings for Qt5 and Qt6 cannot be built simultaneously.
 ***]])
+fi
+
+# Ensure that pkg-config is available for all calls of FIND_QT5/FIND_QT6
+PKG_PROG_PKG_CONFIG
+
+# If the generic qt is enabled, then check for Qt5 or Qt6 (in this order)
+LIST_MEMBER("qt", $enabled_languages)
+if test "$found" = "1"; then
+    # Remove the generic qt (qt5 and qt6 have already been removed)
+    enabled_languages=$(echo $enabled_languages | sed 's/qt//')
+    FIND_QT5
+    if test "$have_qt5_libs" = "yes"; then
+        want_qt5="yes";
+    else
+        FIND_QT6
+        if test "$have_qt6_libs" = "yes"; then
+            want_qt6="yes";
         else
-            enabled_languages=$(echo $enabled_languages | sed 's/cpp//')
-            enabled_languages=$(echo $enabled_languages | sed 's/qt//')
-            AC_MSG_WARN([[
+            if test "$explicit_languages" = "1"; then
+                AC_MSG_ERROR([[
 ***
-*** No c++11 support detected. C++ and Qt bindings will be disabled.
+*** Qt5 (Qt5Core) or Qt6 (Qt6Core) is required for the Qt binding.
 ***]])
+            else
+                AC_MSG_WARN([[
+***
+*** Qt5 (Qt5Core) and Qt6 (Qt6Core) not found. Qt Binding will be disabled.
+***]])
+            fi
         fi
     fi
-fi
-
-# Check whether compiler supports visibility attribute (if cpp language is enabled)
-LIST_MEMBER("cpp", $enabled_languages)
-if test "$found" = "1"; then
-    AX_GCC_FUNC_ATTRIBUTE(visibility)
-    if test "$ax_cv_have_func_attribute_visibility" = "yes"; then
-        GPGME_CPP_CFLAGS="$GPGME_CPP_CFLAGS -fvisibility=hidden"
+elif test "$want_qt5" = "yes"; then
+    FIND_QT5
+    if test "$have_qt5_libs" != "yes"; then
+        AC_MSG_ERROR([[
+***
+*** Qt5 (Qt5Core) is required for the Qt 5 binding.
+***]])
+    fi
+elif test "$want_qt6" = "yes"; then
+    FIND_QT6
+    if test "$have_qt6_libs" != "yes"; then
+        AC_MSG_ERROR([[
+***
+*** Qt6 (Qt6Core) is required for the Qt 6 binding.
+***]])
     fi
 fi
-AC_SUBST(GPGME_CPP_CFLAGS)
 
-# Check that if qt is enabled cpp also is enabled
-LIST_MEMBER("qt", $enabled_languages)
-if test "$found" = "1"; then
-    # We need to ensure that in the language order qt comes after cpp
-    # so we remove qt first and explicitly add it as last list member.
-    enabled_languages=$(echo $enabled_languages | sed 's/qt//')
+# Check that cpp is enabled if qt5 or qt6 is enabled
+if test "$want_qt5" = "yes" -o "$want_qt6" = "yes"; then
     LIST_MEMBER("cpp", $enabled_languages)
     if test "$found" = "0"; then
         AC_MSG_ERROR([[
 ***
-*** Qt language binding depends on cpp binding.
+*** The Qt bindings depend on the C++ binding.
 ***]])
     fi
-    FIND_QT5
-    if test "$have_qt5_libs" != "yes"; then
+fi
+
+# Enable C++ 17 if qt6 is requested
+if test "$want_qt6" = "yes"; then
+    AX_CXX_COMPILE_STDCXX(17, noext, optional)
+    if test "$HAVE_CXX17" != "1"; then
         if test "$explicit_languages" = "1"; then
-        AC_MSG_ERROR([[
+            AC_MSG_ERROR([[
 ***
-*** Qt5 (Qt5Core) is required for Qt binding.
+*** A compiler with c++17 support is required for the Qt 6 binding.
 ***]])
         else
-           AC_MSG_WARN([[
+            want_qt6="no"
+            AC_MSG_WARN([[
 ***
-*** Qt5 (Qt5Core) not found Qt Binding will be disabled.
+*** No c++17 support detected. Qt 6 binding will be disabled.
 ***]])
         fi
-    else
-        enabled_languages=`echo $enabled_languages qt`
+    fi
+fi
 
-        AC_CHECK_PROGS([DOXYGEN], [doxygen])
-        if test -z "$DOXYGEN";
-            # This is not highlighted because it's not really important.
-            then AC_MSG_WARN([Doxygen not found - Qt binding doc will not be built.])
-        fi
-        AC_CHECK_PROGS([GRAPHVIZ], [dot])
-        if test -z "$GRAPHVIZ";
-            then AC_MSG_WARN([Graphviz not found - Qt binding doc will not have diagrams.])
+# Enable C++ 11 if cpp is requested (unless C++ 17 was already enabled)
+LIST_MEMBER("cpp", $enabled_languages)
+if test "$found" = "1" -a "$HAVE_CXX17" != "1"; then
+    AX_CXX_COMPILE_STDCXX(11, noext, optional)
+    if test "$HAVE_CXX11" != "1"; then
+        if test "$explicit_languages" = "1"; then
+            AC_MSG_ERROR([[
+***
+*** A compiler with c++11 support is required for the C++ binding.
+***]])
+        else
+            enabled_languages=$(echo $enabled_languages | sed 's/cpp//')
+            want_qt5="no"
+            AC_MSG_WARN([[
+***
+*** No c++11 support detected. C++ and Qt 5 bindings will be disabled.
+***]])
         fi
     fi
 fi
 
-# Check if compiler supports visibility attribute (if qt is enabled)
-LIST_MEMBER("qt", $enabled_languages)
+# Now append qt to the list of language bindings
+if test "$want_qt5" = "yes" -o "$want_qt6" = "yes"; then
+    enabled_languages=$(echo $enabled_languages qt)
+fi
+
+# Check whether compiler supports visibility attribute (if cpp language is enabled)
+LIST_MEMBER("cpp", $enabled_languages)
 if test "$found" = "1"; then
     AX_GCC_FUNC_ATTRIBUTE(visibility)
     if test "$ax_cv_have_func_attribute_visibility" = "yes"; then
-        GPGME_QT5_CFLAGS="$GPGME_QT5_CFLAGS -fvisibility=hidden"
+        GPGME_CPP_CFLAGS="$GPGME_CPP_CFLAGS -fvisibility=hidden"
+        if test "$want_qt5" = "yes"; then
+            GPGME_QT5_CFLAGS="$GPGME_QT5_CFLAGS -fvisibility=hidden"
+        fi
+        if test "$want_qt6" = "yes"; then
+            GPGME_QT6_CFLAGS="$GPGME_QT6_CFLAGS -fvisibility=hidden"
+        fi
+    fi
+fi
+AC_SUBST(GPGME_CPP_CFLAGS)
+
+AM_CONDITIONAL(WANT_QT5, test "$want_qt5" = yes)
+AM_CONDITIONAL(WANT_QT6, test "$want_qt6" = yes)
+
+# Check for tools for building the Qt binding docs
+if test "$want_qt5" = "yes" -o "$want_qt6" = "yes"; then
+    AC_CHECK_PROGS([DOXYGEN], [doxygen])
+    if test -z "$DOXYGEN"; then
+        # This is not highlighted because it's not really important.
+        AC_MSG_WARN([Doxygen not found - Qt binding doc will not be built.])
+    fi
+    AC_CHECK_PROGS([GRAPHVIZ], [dot])
+    if test -z "$GRAPHVIZ"; then
+        AC_MSG_WARN([Graphviz not found - Qt binding doc will not have diagrams.])
     fi
 fi
 
@@ -967,9 +1045,16 @@ AC_CONFIG_FILES(lang/cpp/src/GpgmeppConfig.cmake.in)
 AC_CONFIG_FILES(lang/cpp/src/GpgmeppConfigVersion.cmake)
 AC_CONFIG_FILES(lang/cpp/src/gpgmepp_version.h)
 AC_CONFIG_FILES(lang/qt/Makefile lang/qt/src/Makefile)
-AC_CONFIG_FILES(lang/qt/src/QGpgmeConfig-w32.cmake.in)
-AC_CONFIG_FILES(lang/qt/src/QGpgmeConfig.cmake.in)
-AC_CONFIG_FILES(lang/qt/src/QGpgmeConfigVersion.cmake)
+if test "$want_qt5" = "yes"; then
+    AC_CONFIG_FILES(lang/qt/src/QGpgmeConfig-w32.cmake.in)
+    AC_CONFIG_FILES(lang/qt/src/QGpgmeConfig.cmake.in)
+    AC_CONFIG_FILES(lang/qt/src/QGpgmeConfigVersion.cmake)
+fi
+if test "$want_qt6" = "yes"; then
+    AC_CONFIG_FILES(lang/qt/src/QGpgmeQt6Config-w32.cmake.in)
+    AC_CONFIG_FILES(lang/qt/src/QGpgmeQt6Config.cmake.in)
+    AC_CONFIG_FILES(lang/qt/src/QGpgmeQt6ConfigVersion.cmake)
+fi
 AC_CONFIG_FILES(lang/qt/tests/Makefile)
 AC_CONFIG_FILES(lang/qt/src/qgpgme_version.h)
 AC_CONFIG_FILES([lang/Makefile lang/cl/Makefile lang/cl/gpgme.asd])
@@ -987,6 +1072,12 @@ AC_CONFIG_FILES([lang/python/Makefile
 AC_CONFIG_FILES([lang/python/setup.py], [chmod a+x lang/python/setup.py])
 AC_OUTPUT
 
+if test "$want_qt5" = "yes"; then
+    enabled_languages_v=$(echo ${enabled_languages_v:-$enabled_languages} | sed "s/qt/qt (Qt 5)/")
+elif test "$want_qt6" = "yes"; then
+    enabled_languages_v=$(echo ${enabled_languages_v:-$enabled_languages} | sed "s/qt/qt (Qt 6)/")
+fi
+
 echo "
         GPGME v${VERSION} has been configured as follows:
 
diff --git a/lang/qt/src/Makefile.am b/lang/qt/src/Makefile.am
index aa03cc72..9ad826e9 100644
--- a/lang/qt/src/Makefile.am
+++ b/lang/qt/src/Makefile.am
@@ -18,10 +18,18 @@
 # along with this program; if not, write to the Free Software
 # Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
 # 02111-1307, USA
+
+if WANT_QT5
 lib_LTLIBRARIES = libqgpgme.la
+endif
+if WANT_QT6
+lib_LTLIBRARIES = libqgpgmeqt6.la
+endif
+
 EXTRA_DIST = QGpgmeConfig.cmake.in.in QGpgmeConfigVersion.cmake.in \
              qgpgme_debug.h qgpgme_version.h.in \
-             QGpgmeConfig-w32.cmake.in.in
+             QGpgmeConfig-w32.cmake.in.in QGpgmeQt6Config.cmake.in.in \
+             QGpgmeQt6Config-w32.cmake.in.in QGpgmeQt6ConfigVersion.cmake.in
 
 qgpgme_sources = \
     dataprovider.cpp \
@@ -258,17 +266,32 @@ camelcaseincludedir = $(includedir)/QGpgME
 camelcaseinclude_HEADERS = $(camelcase_headers)
 nodist_qgpgmeinclude_HEADERS = qgpgme_version.h
 
-libqgpgme_la_SOURCES = $(qgpgme_sources) $(qgpgme_headers) $(private_qgpgme_headers)
-
+if WANT_QT5
 AM_CPPFLAGS = -I$(top_srcdir)/lang/cpp/src -I$(top_builddir)/src \
               @GPGME_QT5_CFLAGS@ @GPG_ERROR_CFLAGS@ @LIBASSUAN_CFLAGS@ \
               -DBUILDING_QGPGME -Wsuggest-override \
               -Wzero-as-null-pointer-constant
 
+libqgpgme_la_SOURCES = $(qgpgme_sources) $(qgpgme_headers) $(private_qgpgme_headers)
+
 libqgpgme_la_LIBADD = ../../cpp/src/libgpgmepp.la ../../../src/libgpgme.la \
-                       @LIBASSUAN_LIBS@ @GPG_ERROR_LIBS@ @GPGME_QT5_LIBS@
+                      @LIBASSUAN_LIBS@ @GPG_ERROR_LIBS@ @GPGME_QT5_LIBS@
 libqgpgme_la_LDFLAGS = -no-undefined -version-info \
-    @LIBQGPGME_LT_CURRENT@:@LIBQGPGME_LT_REVISION@:@LIBQGPGME_LT_AGE@
+                       @LIBQGPGME_LT_CURRENT@:@LIBQGPGME_LT_REVISION@:@LIBQGPGME_LT_AGE@
+endif
+if WANT_QT6
+AM_CPPFLAGS = -I$(top_srcdir)/lang/cpp/src -I$(top_builddir)/src \
+              @GPGME_QT6_CFLAGS@ @GPG_ERROR_CFLAGS@ @LIBASSUAN_CFLAGS@ \
+              -DBUILDING_QGPGME -Wsuggest-override \
+              -Wzero-as-null-pointer-constant
+
+libqgpgmeqt6_la_SOURCES = $(qgpgme_sources) $(qgpgme_headers) $(private_qgpgme_headers)
+
+libqgpgmeqt6_la_LIBADD = ../../cpp/src/libgpgmepp.la ../../../src/libgpgme.la \
+                         @LIBASSUAN_LIBS@ @GPG_ERROR_LIBS@ @GPGME_QT6_LIBS@
+libqgpgmeqt6_la_LDFLAGS = -no-undefined -version-info \
+                          @LIBQGPGME_LT_CURRENT@:@LIBQGPGME_LT_REVISION@:@LIBQGPGME_LT_AGE@
+endif
 
 if HAVE_MACOS_SYSTEM
 libsuffix=.dylib
@@ -276,6 +299,7 @@ else
 libsuffix=.so
 endif
 
+if WANT_QT5
 if HAVE_W32_SYSTEM
 QGpgmeConfig.cmake: QGpgmeConfig-w32.cmake.in
 	sed -e 's|[@]resolved_bindir@|$(bindir)|g' < "$<" | \
@@ -287,23 +311,52 @@ QGpgmeConfig.cmake: QGpgmeConfig.cmake.in
 	sed -e 's|[@]libsuffix@|$(libsuffix)|g' | \
 	sed -e 's|[@]resolved_includedir@|$(includedir)|g' > $@
 endif
+endif
+if WANT_QT6
+if HAVE_W32_SYSTEM
+QGpgmeQt6Config.cmake: QGpgmeQt6Config-w32.cmake.in
+	sed -e 's|[@]resolved_bindir@|$(bindir)|g' < "$<" | \
+	sed -e 's|[@]resolved_libdir@|$(libdir)|g' | \
+	sed -e 's|[@]resolved_includedir@|$(includedir)|g' > $@
+else
+QGpgmeQt6Config.cmake: QGpgmeQt6Config.cmake.in
+	sed -e 's|[@]resolved_libdir@|$(libdir)|g' < "$<" | \
+	sed -e 's|[@]libsuffix@|$(libsuffix)|g' | \
+	sed -e 's|[@]resolved_includedir@|$(includedir)|g' > $@
+endif
+endif
 
 $(camelcase_headers): Makefile.am
 	echo -n "#include \"qgpgme/" > "$@"
 	echo -n "$@" | tr '[:upper:]' '[:lower:]' >> "$@"
 	echo ".h\"" >> "$@"
 
+if WANT_QT5
 install-cmake-files: QGpgmeConfig.cmake QGpgmeConfigVersion.cmake
 	-$(INSTALL) -d $(DESTDIR)$(libdir)/cmake/QGpgme
 	$(INSTALL) -m 644 QGpgmeConfig.cmake \
-        $(DESTDIR)$(libdir)/cmake/QGpgme/QGpgmeConfig.cmake
+	$(DESTDIR)$(libdir)/cmake/QGpgme/QGpgmeConfig.cmake
 	$(INSTALL) -m 644 QGpgmeConfigVersion.cmake \
-        $(DESTDIR)$(libdir)/cmake/QGpgme/QGpgmeConfigVersion.cmake
+	$(DESTDIR)$(libdir)/cmake/QGpgme/QGpgmeConfigVersion.cmake
 
 uninstall-cmake-files:
 	-rm $(DESTDIR)$(libdir)/cmake/QGpgme/QGpgmeConfigVersion.cmake
 	-rm $(DESTDIR)$(libdir)/cmake/QGpgme/QGpgmeConfig.cmake
 	-rmdir $(DESTDIR)$(libdir)/cmake/QGpgme/
+endif
+if WANT_QT6
+install-cmake-files: QGpgmeQt6Config.cmake QGpgmeQt6ConfigVersion.cmake
+	-$(INSTALL) -d $(DESTDIR)$(libdir)/cmake/QGpgmeQt6
+	$(INSTALL) -m 644 QGpgmeQt6Config.cmake \
+	$(DESTDIR)$(libdir)/cmake/QGpgmeQt6/QGpgmeQt6Config.cmake
+	$(INSTALL) -m 644 QGpgmeQt6ConfigVersion.cmake \
+	$(DESTDIR)$(libdir)/cmake/QGpgmeQt6/QGpgmeQt6ConfigVersion.cmake
+
+uninstall-cmake-files:
+	-rm $(DESTDIR)$(libdir)/cmake/QGpgmeQt6/QGpgmeQt6ConfigVersion.cmake
+	-rm $(DESTDIR)$(libdir)/cmake/QGpgmeQt6/QGpgmeQt6Config.cmake
+	-rmdir $(DESTDIR)$(libdir)/cmake/QGpgmeQt6/
+endif
 
 install-data-local: install-cmake-files
 
@@ -313,9 +366,15 @@ BUILT_SOURCES = $(qgpgme_moc_sources) $(camelcase_headers)
 
 CLEANFILES = $(qgpgme_moc_sources) $(camelcase_headers) QGpgmeConfig.cmake \
              qgpgme_version.h QGpgmeConfig.cmake.in \
-             QGpgmeConfigVersion.cmake
+             QGpgmeConfigVersion.cmake QGpgmeQt6Config.cmake.in \
+             QGpgmeQt6Config.cmake QGpgmeQt6ConfigVersion.cmake
 
+if WANT_QT5
 nodist_libqgpgme_la_SOURCES = $(qgpgme_moc_sources)
+endif
+if WANT_QT6
+nodist_libqgpgmeqt6_la_SOURCES = $(qgpgme_moc_sources)
+endif
 
 .h.moc:
 	$(MOC) `test -f '$<' || echo '$(srcdir)/'`$< -o $@
diff --git a/lang/qt/src/QGpgmeQt6Config-w32.cmake.in.in b/lang/qt/src/QGpgmeQt6Config-w32.cmake.in.in
new file mode 100644
index 00000000..6cb8af40
--- /dev/null
+++ b/lang/qt/src/QGpgmeQt6Config-w32.cmake.in.in
@@ -0,0 +1,105 @@
+# CMake Config file for QGpgME for Qt 6
+# Copyright (C) 2016 Intevation GmbH
+#
+# This file is part of GPGME.
+#
+# QGpgME is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# QGpgME is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+# 02111-1307, USA
+
+# based on a generated file from cmake.
+# Generated by CMake 3.0.2
+
+if("${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION}" LESS 2.5)
+   message(FATAL_ERROR "CMake >= 2.6.0 required")
+endif()
+cmake_policy(PUSH)
+cmake_policy(VERSION 2.6)
+#----------------------------------------------------------------
+# Generated CMake target import file.
+#----------------------------------------------------------------
+
+# Commands may need to know the format version.
+set(CMAKE_IMPORT_FILE_VERSION 1)
+
+# Protect against multiple inclusion, which would fail when already imported targets are added once more.
+set(_targetsDefined)
+set(_targetsNotDefined)
+set(_expectedTargets)
+foreach(_expectedTarget QGpgmeQt6)
+  list(APPEND _expectedTargets ${_expectedTarget})
+  if(NOT TARGET ${_expectedTarget})
+    list(APPEND _targetsNotDefined ${_expectedTarget})
+  endif()
+  if(TARGET ${_expectedTarget})
+    list(APPEND _targetsDefined ${_expectedTarget})
+  endif()
+endforeach()
+if("${_targetsDefined}" STREQUAL "${_expectedTargets}")
+  set(CMAKE_IMPORT_FILE_VERSION)
+  cmake_policy(POP)
+  return()
+endif()
+if(NOT "${_targetsDefined}" STREQUAL "")
+  message(FATAL_ERROR "Some (but not all) targets in this export set were already defined.\nTargets Defined: ${_targetsDefined}\nTargets not yet defined: ${_targetsNotDefined}\n")
+endif()
+unset(_targetsDefined)
+unset(_targetsNotDefined)
+unset(_expectedTargets)
+
+# Create imported target QGpgmeQt6
+add_library(QGpgmeQt6 SHARED IMPORTED)
+
+set_target_properties(QGpgmeQt6 PROPERTIES
+  IMPORTED_IMPLIB_RELEASE "@resolved_libdir@/libqgpgmeqt6.dll.a"
+  INTERFACE_INCLUDE_DIRECTORIES "@resolved_includedir@/qgpgme;@resolved_includedir@"
+  INTERFACE_LINK_LIBRARIES "Gpgmepp;Qt6::Core"
+  IMPORTED_LOCATION "@resolved_libdir@/libqgpgmeqt6-7.dll"
+)
+
+list(APPEND _IMPORT_CHECK_TARGETS QGpgmeQt6 )
+list(APPEND _IMPORT_CHECK_FILES_FOR_QGpgmeQt6 "@resolved_libdir@/libqgpgmeqt6.dll.a" "@resolved_bindir@/libqgpgmeqt6-7.dll" )
+
+if(CMAKE_VERSION VERSION_LESS 2.8.12)
+  message(FATAL_ERROR "This file relies on consumers using CMake 2.8.12 or greater.")
+endif()
+
+# Loop over all imported files and verify that they actually exist
+foreach(target ${_IMPORT_CHECK_TARGETS} )
+  foreach(file ${_IMPORT_CHECK_FILES_FOR_${target}} )
+    if(NOT EXISTS "${file}" )
+      message(FATAL_ERROR "The imported target \"${target}\" references the file
+   \"${file}\"
+but this file does not exist.  Possible reasons include:
+* The file was deleted, renamed, or moved to another location.
+* An install or uninstall procedure did not complete successfully.
+* The installation package was faulty and contained
+   \"${CMAKE_CURRENT_LIST_FILE}\"
+but not all the files it references.
+")
+    endif()
+  endforeach()
+  unset(_IMPORT_CHECK_FILES_FOR_${target})
+endforeach()
+unset(_IMPORT_CHECK_TARGETS)
+
+# This file does not depend on other imported targets which have
+# been exported from the same project but in a separate export set.
+
+# Commands beyond this point should not need to know the version.
+set(CMAKE_IMPORT_FILE_VERSION)
+cmake_policy(POP)
+
+# Gpgmepp is a requirement for QGpgME
+find_package(Gpgmepp CONFIG REQUIRED)
diff --git a/lang/qt/src/QGpgmeQt6Config.cmake.in.in b/lang/qt/src/QGpgmeQt6Config.cmake.in.in
new file mode 100644
index 00000000..b539922f
--- /dev/null
+++ b/lang/qt/src/QGpgmeQt6Config.cmake.in.in
@@ -0,0 +1,101 @@
+# CMake Config file for QGpgME for Qt 6
+# Copyright (C) 2016 Intevation GmbH
+#
+# This file is part of GPGME.
+#
+# QGpgME is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# QGpgME is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+# 02111-1307, USA
+
+# based on a generated file from cmake.
+# Generated by CMake 3.0.2
+
+if("${CMAKE_MAJOR_VERSION}.${CMAKE_MINOR_VERSION}" LESS 2.5)
+   message(FATAL_ERROR "CMake >= 2.6.0 required")
+endif()
+cmake_policy(PUSH)
+cmake_policy(VERSION 2.6)
+#----------------------------------------------------------------
+# Generated CMake target import file.
+#----------------------------------------------------------------
+
+# Commands may need to know the format version.
+set(CMAKE_IMPORT_FILE_VERSION 1)
+
+# Protect against multiple inclusion, which would fail when already imported targets are added once more.
+set(_targetsDefined)
+set(_targetsNotDefined)
+set(_expectedTargets)
+foreach(_expectedTarget QGpgmeQt6)
+  list(APPEND _expectedTargets ${_expectedTarget})
+  if(NOT TARGET ${_expectedTarget})
+    list(APPEND _targetsNotDefined ${_expectedTarget})
+  endif()
+  if(TARGET ${_expectedTarget})
+    list(APPEND _targetsDefined ${_expectedTarget})
+  endif()
+endforeach()
+if("${_targetsDefined}" STREQUAL "${_expectedTargets}")
+  set(CMAKE_IMPORT_FILE_VERSION)
+  cmake_policy(POP)
+  return()
+endif()
+if(NOT "${_targetsDefined}" STREQUAL "")
+  message(FATAL_ERROR "Some (but not all) targets in this export set were already defined.\nTargets Defined: ${_targetsDefined}\nTargets not yet defined: ${_targetsNotDefined}\n")
+endif()
+unset(_targetsDefined)
+unset(_targetsNotDefined)
+unset(_expectedTargets)
+
+# Create imported target QGpgmeQt6
+add_library(QGpgmeQt6 SHARED IMPORTED)
+
+set_target_properties(QGpgmeQt6 PROPERTIES
+  INTERFACE_INCLUDE_DIRECTORIES "@resolved_includedir@/qgpgme;@resolved_includedir@"
+  INTERFACE_LINK_LIBRARIES "Gpgmepp;Qt6::Core"
+  IMPORTED_LOCATION "@resolved_libdir@/libqgpgmeqt6@libsuffix@"
+)
+
+if(CMAKE_VERSION VERSION_LESS 2.8.12)
+  message(FATAL_ERROR "This file relies on consumers using CMake 2.8.12 or greater.")
+endif()
+
+# Loop over all imported files and verify that they actually exist
+foreach(target ${_IMPORT_CHECK_TARGETS} )
+  foreach(file ${_IMPORT_CHECK_FILES_FOR_${target}} )
+    if(NOT EXISTS "${file}" )
+      message(FATAL_ERROR "The imported target \"${target}\" references the file
+   \"${file}\"
+but this file does not exist.  Possible reasons include:
+* The file was deleted, renamed, or moved to another location.
+* An install or uninstall procedure did not complete successfully.
+* The installation package was faulty and contained
+   \"${CMAKE_CURRENT_LIST_FILE}\"
+but not all the files it references.
+")
+    endif()
+  endforeach()
+  unset(_IMPORT_CHECK_FILES_FOR_${target})
+endforeach()
+unset(_IMPORT_CHECK_TARGETS)
+
+# This file does not depend on other imported targets which have
+# been exported from the same project but in a separate export set.
+
+# Commands beyond this point should not need to know the version.
+set(CMAKE_IMPORT_FILE_VERSION)
+cmake_policy(POP)
+
+# Gpgmepp is a requirement for QGpgME
+find_package(Gpgmepp CONFIG REQUIRED)
diff --git a/lang/qt/src/QGpgmeQt6ConfigVersion.cmake.in b/lang/qt/src/QGpgmeQt6ConfigVersion.cmake.in
new file mode 100644
index 00000000..eaa60dc8
--- /dev/null
+++ b/lang/qt/src/QGpgmeQt6ConfigVersion.cmake.in
@@ -0,0 +1,31 @@
+# CMake Version file for QGpgME for Qt 6
+# Copyright (C) 2016 Intevation GmbH
+#
+# This file is part of GPGME.
+#
+# QGpgME is free software; you can redistribute it and/or modify it
+# under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# QGpgME is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+# 02111-1307, USA
+
+# based on a generated file from cmake.
+set(PACKAGE_VERSION "@VERSION_MAJOR@.@VERSION_MINOR@.@VERSION_MICRO@")
+
+if("${PACKAGE_VERSION}" VERSION_LESS "${PACKAGE_FIND_VERSION}" )
+  set(PACKAGE_VERSION_COMPATIBLE FALSE)
+else()
+  set(PACKAGE_VERSION_COMPATIBLE TRUE)
+  if("${PACKAGE_FIND_VERSION}" STREQUAL "${PACKAGE_VERSION}")
+    set(PACKAGE_VERSION_EXACT TRUE)
+  endif()
+endif()
diff --git a/lang/qt/tests/Makefile.am b/lang/qt/tests/Makefile.am
index a1d1b82f..564a9ff7 100644
--- a/lang/qt/tests/Makefile.am
+++ b/lang/qt/tests/Makefile.am
@@ -44,6 +44,7 @@ moc_files = \
 
 AM_LDFLAGS = -no-install
 
+if WANT_QT5
 LDADD = ../../cpp/src/libgpgmepp.la ../src/libqgpgme.la \
         ../../../src/libgpgme.la @GPGME_QT5_LIBS@ @GPG_ERROR_LIBS@ \
         @GPGME_QT5TEST_LIBS@ @LDADD_FOR_TESTS_KLUDGE@ -lstdc++
@@ -53,6 +54,18 @@ AM_CPPFLAGS = -I$(top_srcdir)/lang/cpp/src -I$(top_builddir)/src \
               @LIBASSUAN_CFLAGS@ @GPGME_QT5TEST_CFLAGS@ -DBUILDING_QGPGME \
               -I$(top_srcdir)/lang/qt/src \
               -DTOP_SRCDIR="$(top_srcdir)"
+endif
+if WANT_QT6
+LDADD = ../../cpp/src/libgpgmepp.la ../src/libqgpgmeqt6.la \
+        ../../../src/libgpgme.la @GPGME_QT6_LIBS@ @GPG_ERROR_LIBS@ \
+        @GPGME_QT6TEST_LIBS@ @LDADD_FOR_TESTS_KLUDGE@ -lstdc++
+
+AM_CPPFLAGS = -I$(top_srcdir)/lang/cpp/src -I$(top_builddir)/src \
+              @GPG_ERROR_CFLAGS@ @GPGME_QT6_CFLAGS@ @GPG_ERROR_CFLAGS@ \
+              @LIBASSUAN_CFLAGS@ @GPGME_QT6TEST_CFLAGS@ -DBUILDING_QGPGME \
+              -I$(top_srcdir)/lang/qt/src \
+              -DTOP_SRCDIR="$(top_srcdir)"
+endif
 
 support_src = t-support.h t-support.cpp
 
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
+])