Add FreeBSD support (#358)

* chore: don't use systemd headers with elogind

In file included from src/VTableUtils.c:27:
src/VTableUtils.h:30:10: fatal error: 'systemd/sd-bus.h' file not found
 #include <systemd/sd-bus.h>
          ^~~~~~~~~~~~~~~~~~

* chore: add basu support

Similar to elogind but also supported on non-Linux.

* chore(tests): permit /var/lib/machine-id on non-systemd

https://github.com/elogind/elogind/commit/84fdc0fc61c1
https://git.sr.ht/~emersion/basu/commit/8324e6729231

* chore(ci): add simple freebsd job

Mainly to cover libc++ and basu.

* chore(ci): explicitly pass CMAKE_INSTALL_PREFIX

Some sdbus-cpp tests require configuring system bus. However, Linux
testing relies on writing outside of prefix in order to affect current
system bus instance instead of launching a dedicated one.

* chore(tests): respect CMAKE_INSTALL_PREFIX for system bus config

DBus isn't part of base system on BSDs, so may not use /etc for configs.
Also, testing installation failed as non-root:

$ cmake -DBUILD_TESTS=1 -DCMAKE_INSTALL_PREFIX=/tmp/sdbus-cpp_prefix -DTESTS_INSTALL_PATH=/tmp/sdbus-cpp_prefix/tests
$ cmake --build .
$ cmake --install .
[...]
CMake Error at tests/cmake_install.cmake:105 (file):
  file cannot create directory: /etc/dbus-1/system.d.  Maybe need
  administrative privileges.

* chore(tests): temporarily skip 1 test on FreeBSD to keep CI happy

* chore(ci): run tests in freebsd job

tests/CMakeLists.txt

@@ -104,7 +104,9 @@ include_directories(${CMAKE_CURRENT_SOURCE_DIR})
 #----------------------------------
 
 add_executable(sdbus-c++-unit-tests ${UNITTESTS_SRCS})
-target_compile_definitions(sdbus-c++-unit-tests PRIVATE LIBSYSTEMD_VERSION=${LIBSYSTEMD_VERSION})
+target_compile_definitions(sdbus-c++-unit-tests PRIVATE
+    LIBSYSTEMD_VERSION=${LIBSYSTEMD_VERSION}
+    SDBUS_HEADER=<${LIBSYSTEMD}/sd-bus.h>)
 target_link_libraries(sdbus-c++-unit-tests sdbus-c++-objlib GTest::gmock)
 
 add_executable(sdbus-c++-integration-tests ${INTEGRATIONTESTS_SRCS})
@@ -138,21 +140,22 @@ endif()
 # INSTALLATION
 #----------------------------------
 
+include(GNUInstallDirs)
 set(TESTS_INSTALL_PATH "/opt/test/bin" CACHE STRING "Specifies where the test binaries will be installed")
 
 install(TARGETS sdbus-c++-unit-tests DESTINATION ${TESTS_INSTALL_PATH} COMPONENT test)
 install(TARGETS sdbus-c++-integration-tests DESTINATION ${TESTS_INSTALL_PATH} COMPONENT test)
-install(FILES ${INTEGRATIONTESTS_SOURCE_DIR}/files/org.sdbuscpp.integrationtests.conf DESTINATION /etc/dbus-1/system.d COMPONENT test)
+install(FILES ${INTEGRATIONTESTS_SOURCE_DIR}/files/org.sdbuscpp.integrationtests.conf DESTINATION ${CMAKE_INSTALL_FULL_SYSCONFDIR}/dbus-1/system.d COMPONENT test)
 
 if(ENABLE_PERF_TESTS)
     install(TARGETS sdbus-c++-perf-tests-client DESTINATION ${TESTS_INSTALL_PATH} COMPONENT test)
     install(TARGETS sdbus-c++-perf-tests-server DESTINATION ${TESTS_INSTALL_PATH} COMPONENT test)
-    install(FILES ${PERFTESTS_SOURCE_DIR}/files/org.sdbuscpp.perftests.conf DESTINATION /etc/dbus-1/system.d COMPONENT test)
+    install(FILES ${PERFTESTS_SOURCE_DIR}/files/org.sdbuscpp.perftests.conf DESTINATION ${CMAKE_INSTALL_FULL_SYSCONFDIR}/dbus-1/system.d COMPONENT test)
 endif()
 
 if(ENABLE_STRESS_TESTS)
     install(TARGETS sdbus-c++-stress-tests DESTINATION ${TESTS_INSTALL_PATH} COMPONENT test)
-    install(FILES ${STRESSTESTS_SOURCE_DIR}/files/org.sdbuscpp.stresstests.conf DESTINATION /etc/dbus-1/system.d COMPONENT test)
+    install(FILES ${STRESSTESTS_SOURCE_DIR}/files/org.sdbuscpp.stresstests.conf DESTINATION ${CMAKE_INSTALL_FULL_SYSCONFDIR}/dbus-1/system.d COMPONENT test)
 endif()
 
 #----------------------------------

tests/integrationtests/DBusMethodsTests.cpp

@@ -277,6 +277,10 @@ TEST_F(SdbusTestObject, CannotSetGeneralMethodTimeoutWithLibsystemdVersionLessTh
 
 TEST_F(SdbusTestObject, CanCallMethodSynchronouslyWithoutAnEventLoopThread)
 {
+#if defined(__clang__) && defined(__FreeBSD__)
+    GTEST_SKIP() << "https://github.com/Kistler-Group/sdbus-cpp/issues/359";
+#endif
+
     auto proxy = std::make_unique<TestProxy>(BUS_NAME, OBJECT_PATH, sdbus::dont_run_event_loop_thread);
 
     auto multiplyRes = proxy->multiply(INT64_VALUE, DOUBLE_VALUE);

tests/integrationtests/DBusStandardInterfacesTests.cpp

@@ -61,12 +61,9 @@ TEST_F(SdbusTestObject, PingsViaPeerInterface)
 
 TEST_F(SdbusTestObject, AnswersMachineUuidViaPeerInterface)
 {
-    // If /etc/machine-id does not exist in your system (which is very likely because you have
-    // a non-systemd Linux), org.freedesktop.DBus.Peer.GetMachineId() will not work. To solve
-    // this, you can create /etc/machine-id yourself as symlink to /var/lib/dbus/machine-id,
-    // and then org.freedesktop.DBus.Peer.GetMachineId() will start to work.
-    if (::access("/etc/machine-id", F_OK) == -1)
-        GTEST_SKIP() << "/etc/machine-id file does not exist, GetMachineId() will not work";
+    if (::access("/etc/machine-id", F_OK) == -1 &&
+        ::access("/var/lib/dbus/machine-id", F_OK) == -1)
+        GTEST_SKIP() << "/etc/machine-id and /var/lib/dbus/machine-id files do not exist, GetMachineId() will not work";
 
     ASSERT_NO_THROW(m_proxy->GetMachineId());
 }