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, 101 insertions, 0 deletions

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)