Make fff installable

This commit make fff installable, via `cmake --install <build-dir>
--prefix <some-install-prefix>` for example.  During installation,
imported targets are created, such that users are able to fff like
this:

```cmake
find_package(fff REQUIRED)

add_executable(some_test some_test.ccp)
target_link_libraries(some_test PRIVATE fff::fff)
´´´

This won't affect users who embed fff in their source trees,

Furthermore, if `FFF_GENERATE` is enable, fff.h is generated into the
build folder, instead of overwriting the pre-generated fff.h.

CMakeLists.txt

@@ -9,38 +9,57 @@ set(CMAKE_CXX_STANDARD 11)
 # Enable ctest
 enable_testing()
 
-add_library(fff INTERFACE)
-
 option(FFF_GENERATE "If enabled, fff.h will be regenerated using ruby" OFF)
 
 # Generate fff.h if fakegen.rb changed
 if(FFF_GENERATE)
+ find_package(Ruby REQUIRED)
+
  add_custom_command(
  OUTPUT
- ${CMAKE_CURRENT_LIST_DIR}/fff.h
+ ${CMAKE_BINARY_DIR}/fff.h
  COMMAND
- ruby ${CMAKE_CURRENT_LIST_DIR}/fakegen.rb >> ${CMAKE_CURRENT_LIST_DIR}/fff.h
+ ${Ruby_EXECUTABLE} ${CMAKE_CURRENT_LIST_DIR}/fakegen.rb >> ${CMAKE_BINARY_DIR}/fff.h
  DEPENDS
  ${CMAKE_CURRENT_LIST_DIR}/fakegen.rb
  ${CMAKE_CURRENT_LIST_DIR}/LICENSE
  )
- add_custom_target(fff_h DEPENDS ${CMAKE_CURRENT_LIST_DIR}/fff.h)
+ add_library(fff INTERFACE ${CMAKE_BINARY_DIR}/fff.h)
+ target_include_directories(fff INTERFACE
+ $<BUILD_INTERFACE:${CMAKE_BINARY_DIR}>
+ $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+ )
+ set_target_properties(fff
+ PROPERTIES PUBLIC_HEADER "${CMAKE_BINARY_DIR}/fff.h"
+ )
 else()
- add_library(fff_h INTERFACE)
- set_target_properties(fff_h
+ add_library(fff INTERFACE)
+ target_include_directories(fff INTERFACE
+ $<BUILD_INTERFACE:${CMAKE_SOURCE_DIR}>
+ $<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>
+ )
+ set_target_properties(fff
  PROPERTIES PUBLIC_HEADER "fff.h"
  )
 endif()
 
-add_dependencies(fff fff_h)
-
-# Add an interface library for fff.h
-target_include_directories(fff INTERFACE ${CMAKE_CURRENT_LIST_DIR})
-
 option(FFF_UNIT_TESTING "If enabled, fff tests will be compiled and run" OFF)
 
 if(FFF_UNIT_TESTING)
  # Add tests and samples
  add_subdirectory(test)
  add_subdirectory(examples)
 endif()
+
+include(GNUInstallDirs)
+
+install(TARGETS fff EXPORT fffTargets
+ PUBLIC_HEADER
+ INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+)
+install(EXPORT fffTargets
+ FILE fffTargets.cmake
+ NAMESPACE fff::
+ DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/cmake/fff)
+install(FILES fffConfig.cmake
+ DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/cmake/fff)

fffConfig.cmake

@@ -0,0 +1 @@
+include("${CMAKE_CURRENT_LIST_DIR}/fffTargets.cmake")