When install at the system path /usr install the rules file at the pk…

…g config udevdir

CMakeLists.txt

@@ -1370,27 +1370,55 @@ if(UNIX AND NOT APPLE)
   )
 
   option(INSTALL_USER_UDEV_RULES "Install user udev rule file for USB HID and Bulk controllers" ON)
-  if (INSTALL_USER_UDEV_RULES)
-    install(
-      FILES
-        "${CMAKE_CURRENT_SOURCE_DIR}/res/linux/mixxx-usb-uaccess.rules"
-      DESTINATION
-        "${MIXXX_INSTALL_DATADIR}/udev/rules.d"
-    )
-    install(CODE "
-    message(STATUS \"Important Note: Installation of udev rules\n\"
-        \"The udev rule file for USB HID and Bulk controller permissions will be\n\"
-        \"installed to:\n\"
-        \"    ${CMAKE_INSTALL_PREFIX}/${MIXXX_INSTALL_DATADIR}/udev/rules.d.\n\"
-        \"If you are installing Mixxx from source for your own use, copy\n\"
-        \"mixxx-usb-uaccess.rules to /etc/udev/rules.d/ and run:\n\"
-        \"    udevadm control --reload-rules && udevadm trigger\n\"
-        \"as root to load the rules.\n\"
-        \"If you are building a package for a distribution, the correct directory for\n\"
-        \"system rules is either /lib/udev/rules.d (e.g. Debian, Fedora) or\n\"
-        \"/usr/lib/udev/rules.d (e.g. Arch Linux) with an appropriate priority prefix.\n\"
-        \"Adjust your package script accordingly and set -DINSTALL_USER_UDEV_RULES=OFF\")
-    ")
+  if(INSTALL_USER_UDEV_RULES)
+    set(MIXXX_UDEVDIR "${MIXXX_INSTALL_DATADIR}/udev")
+    if (CMAKE_INSTALL_PREFIX STREQUAL "/usr")
+      find_package(PkgConfig)
+      if (PKG_CONFIG_FOUND)
+        pkg_check_modules( PKGCONFIG_UDEV udev)
+        if (PKGCONFIG_UDEV_FOUND)
+	  execute_process(
+	    COMMAND ${PKG_CONFIG_EXECUTABLE} --variable=udevdir udev
+            OUTPUT_VARIABLE PKGCONFIG_UDEVDIR
+            OUTPUT_STRIP_TRAILING_WHITESPACE
+          )
+          if(PKGCONFIG_UDEVDIR)
+	    file(TO_CMAKE_PATH "${PKGCONFIG_UDEVDIR}" MIXXX_UDEVDIR)
+          endif()
+        endif()
+      endif()
+    endif()
+    if (MIXXX_UDEVDIR STREQUAL "${MIXXX_INSTALL_DATADIR}/udev")
+      install(
+        FILES
+          "${CMAKE_CURRENT_SOURCE_DIR}/res/linux/mixxx-usb-uaccess.rules"
+        DESTINATION
+          "${MIXXX_UDEVDIR}/rules.d"
+      )
+      install(CODE "
+      message(STATUS \"Important Note: Installation of udev rules\n\"
+          \"The udev rule file for USB HID and Bulk controller permissions have been\n\"
+          \"installed to:\n\"
+          \"    ${MIXXX_UDEVDIR}/rules.d.\n\"
+          \"If you are installing Mixxx from source for your own use, copy\n\"
+          \"mixxx-usb-uaccess.rules to /etc/udev/rules.d/ and run:\n\"
+          \"    udevadm control --reload-rules && udevadm trigger\n\"
+          \"as root to load the rules.\n\"
+          \"If you are building a package for a distribution, the correct directory for\n\"
+          \"system rules is either /lib/udev/rules.d (e.g. Debian, Fedora) or\n\"
+          \"/usr/lib/udev/rules.d (e.g. Arch Linux) with an appropriate priority prefix.\n\"
+          \"Adjust your package script accordingly and set -DINSTALL_USER_UDEV_RULES=OFF\")
+      ")
+    else()
+      install(
+        FILES
+          "${CMAKE_CURRENT_SOURCE_DIR}/res/linux/mixxx-usb-uaccess.rules"
+        DESTINATION
+          "${MIXXX_UDEVDIR}/rules.d"
+        RENAME
+          "69-mixxx-usb-uaccess.rules"
+      )
+    endif()
   endif()
 endif()