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.

4 files changed, 304 insertions, 8 deletions

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()