Fix glog & gflags cmake interaction

3rdparty/CMakeLists.txt

@@ -8,20 +8,29 @@ else (MSVC)
   add_definitions("-w")
 endif (MSVC)
 
-# This line enables install(EXPORT) in gflags
-# If it's missing, glog complains about it later in the build process
-# Nothing is actually installed due to ECLUDE_FROM_ALL
-set(INSTALL_STATIC_LIBS "ON")
+set(BUILD_TESTING "OFF" CACHE "" INTERNAL)
+
 add_subdirectory(gflags EXCLUDE_FROM_ALL)
 
-# We use target included directly from gflags, so we need to disable find_package for it
-# And trick glog's CMakeLists into believing we have gflags
-set(CMAKE_DISABLE_FIND_PACKAGE_gflags "ON")
+# Do not call find_package for gflags and fill all relevant info manually
+# We cannot make glog link to gflags __target__, because cmake would try to
+# pull it into glog's export set and will get confused and fail
+# Instead we manually specify location and include path for gflags, this way
+# cmake does not create inter-target dependency and export set does not fail
+set(WITH_GFLAGS "OFF" CACHE "" INTERNAL)
+set(HAVE_LIB_GFLAGS "ON")
+set(gflags_NAMESPACE "gflags")
 set(gflags_FOUND "ON")
-# This one tricks cmake into adding correct include dirs, dependent libraries, etc on target_link_libraries call in glog
-set(gflags_LIBRARIES gflags)
+get_target_property(gflags_INCLUDE_DIR gflags INTERFACE_INCLUDE_DIRECTORIES)
+get_target_property(gflags_LIBRARIES gflags INTERFACE_LINK_LIBRARIES)
+set(gflags_LIBRARIES $<TARGET_FILE:gflags> ${gflags_LIBRARIES})
+
 add_subdirectory(glog EXCLUDE_FROM_ALL)
 
+# We need to ask CMake to compile gflags before compiling glog, so that
+# ${gflags_LIBRARIES} actually exists
+add_dependencies(glog gflags)
+
 set(CMAKE_INSTALL_INCLUDEDIR include/artm)
 add_subdirectory(protobuf-3.0.0/cmake EXCLUDE_FROM_ALL)
 set(PROTOBUF_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR}/protobuf-3.0.0/cmake CACHE "" INTERNAL)