build: Control systemd service install precisely

If & where the systemd service files are installed should be
controllable by the user, while keeping a good default*. This commit
adds the flexibility to choose, while keeping the options clear.

*A good default is already provided before this commit and remains the
same.

Signed-off-by: Thijs Paelman <thijs@ouroboros.rocks>
Signed-off-by: Sander Vrijders <sander@ouroboros.rocks>

1 files changed, 46 insertions, 22 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index c69b89b3..22196e64 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -131,29 +131,53 @@ install(FILES "${CMAKE_CURRENT_BINARY_DIR}/ouroboros-irm.pc"
   DESTINATION "${CMAKE_INSTALL_LIBDIR}/pkgconfig")
 
 # modified from https://github.com/ximion/limba
-pkg_check_modules(SYSTEMD "systemd")
-if (SYSTEMD_FOUND)
-  if ("${SYSTEMD_UNITDIR}" STREQUAL "")
-    execute_process(COMMAND ${PKG_CONFIG_EXECUTABLE}
-      --variable=systemdsystemunitdir systemd
-      OUTPUT_VARIABLE SYSTEMD_UNITDIR)
-      string(REGEX REPLACE "[ \t\n]+" "" SYSTEMD_UNITDIR
-      "${SYSTEMD_UNITDIR}"
-    )
-  endif ()
-endif ()
-if (NOT ${SYSTEMD_UNITDIR} STREQUAL "")
-  message(STATUS "Installing systemd service in: ${SYSTEMD_UNITDIR}")
-  if (LIBTOML_LIBRARIES AND NOT DISABLE_CONFIGFILE)
-    set (CONFIGURE_STRING "--config ${OUROBOROS_CONFIG_DIR}${OUROBOROS_CONFIG_FILE}")
-  else ()
-    set (CONFIGURE_STRING "")
+set(SYSTEMD_INSTALL_FILES "DETECT" CACHE STRING
+  "Install systemd .service files (NO (never), DETECT (use pkg-config - default),\
+  FORCE (always - see SYSTEMD_UNITDIR_OVERRIDE))")
+set(SYSTEMD_UNITDIR_OVERRIDE "" CACHE PATH
+  "Path to install systemd files. When SYSTEMD_INSTALL_FILES == DETECT, this\
+  can be empty to automatically determine the path. Cannot be empty when FORCE.")
+
+if (SYSTEMD_INSTALL_FILES STREQUAL "DETECT" OR SYSTEMD_INSTALL_FILES STREQUAL "FORCE")
+  if (SYSTEMD_INSTALL_FILES STREQUAL "DETECT")
+    pkg_check_modules(SYSTEMD "systemd")
+    if (SYSTEMD_FOUND)
+      if ("${SYSTEMD_UNITDIR_OVERRIDE}" STREQUAL "")
+        execute_process(COMMAND ${PKG_CONFIG_EXECUTABLE}
+          --variable=systemdsystemunitdir systemd
+          OUTPUT_VARIABLE SYSTEMD_UNITDIR_INTERNAL)
+          string(REGEX REPLACE "[ \t\n]+" "" SYSTEMD_UNITDIR_INTERNAL
+          "${SYSTEMD_UNITDIR_INTERNAL}"
+        )
+      else ()
+        set(SYSTEMD_UNITDIR_INTERNAL "${SYSTEMD_UNITDIR_OVERRIDE}")
+      endif ()
+    else ()
+      set(SYSTEMD_UNITDIR_INTERNAL "")
+    endif ()
+  elseif (SYSTEMD_INSTALL_FILES STREQUAL "FORCE")
+    if ("${SYSTEMD_UNITDIR_OVERRIDE}" STREQUAL "")
+      message(FATAL_ERROR "Systemd installation required by user, but no path\
+             provided with SYSTEMD_UNITDIR_OVERRIDE.")
+    else ()
+      set(SYSTEMD_UNITDIR_INTERNAL "${SYSTEMD_UNITDIR_OVERRIDE}")
+    endif ()
+  endif()
+  if (NOT ${SYSTEMD_UNITDIR_INTERNAL} STREQUAL "")
+    message(STATUS "Systemd service installation enabled to: ${SYSTEMD_UNITDIR_INTERNAL}")
+    if (LIBTOML_LIBRARIES AND NOT DISABLE_CONFIGFILE)
+      set (CONFIGURE_STRING "--config ${OUROBOROS_CONFIG_DIR}${OUROBOROS_CONFIG_FILE}")
+    else ()
+      set (CONFIGURE_STRING "")
+    endif ()
+    configure_file("${CMAKE_CURRENT_SOURCE_DIR}/ouroboros.service.in"
+      "${CMAKE_CURRENT_BINARY_DIR}/ouroboros.service" @ONLY)
+    install(FILES "${CMAKE_CURRENT_BINARY_DIR}/ouroboros.service"
+      DESTINATION "${SYSTEMD_UNITDIR_INTERNAL}")
   endif ()
-  configure_file("${CMAKE_CURRENT_SOURCE_DIR}/ouroboros.service.in"
-    "${CMAKE_CURRENT_BINARY_DIR}/ouroboros.service" @ONLY)
-  install(FILES "${CMAKE_CURRENT_BINARY_DIR}/ouroboros.service"
-    DESTINATION "${SYSTEMD_UNITDIR}")
-endif ()
+else ()
+  message(STATUS "Systemd service installation disabled by user")
+endif()
 
 enable_testing()
 add_custom_target(check COMMAND ${CMAKE_CTEST_COMMAND})