create and install a pkg-config file on Unix-like systems

CMakeLists.txt

@@ -64,10 +64,14 @@ set_target_properties(olm PROPERTIES
     LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/${CMAKE_INSTALL_LIBDIR}
     RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/${CMAKE_INSTALL_LIBDIR})
 
+include(GNUInstallDirs)
+
+# Make a pkg-config file
+configure_file(${PROJECT_NAME}.pc.in ${PROJECT_NAME}.pc @ONLY NEWLINE_STYLE UNIX)
+
 #
 # Installation
 #
-include(GNUInstallDirs)
 set(INSTALL_CONFIGDIR ${CMAKE_INSTALL_LIBDIR}/cmake/Olm)
 install(TARGETS olm
     EXPORT olm-targets
@@ -86,6 +90,12 @@ install(FILES
     ${CMAKE_CURRENT_SOURCE_DIR}/include/olm/sas.h
     DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/olm)
 
+if (UNIX AND NOT APPLE)
+    install(FILES ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc
+            DESTINATION ${CMAKE_INSTALL_LIBDIR}/pkgconfig
+    )
+endif ()
+
 # Export the targets to a script.
 install(EXPORT olm-targets
   FILE OlmTargets.cmake

olm.pc.in

+prefix=@CMAKE_INSTALL_PREFIX@
+exec_prefix=${prefix}
+includedir=${prefix}/@CMAKE_INSTALL_INCLUDEDIR@
+libdir=${exec_prefix}/@CMAKE_INSTALL_LIBDIR@
+
+Name: olm
+Description: implementation of the Double Ratchet cryptographic ratchet in C++
+Version: @PROJECT_VERSION@
+Cflags: -I${includedir}
+Libs: -L${libdir} -lolm