cmake: Fix rapidJSON version detection

Author: xerrni

CMakeLists.txt

@@ -150,13 +150,21 @@ set_property(SOURCE src/utils.cc APPEND PROPERTY COMPILE_DEFINITIONS
 ### Includes
 
 if(USE_SYSTEM_RAPIDJSON)
-  find_package(RapidJSON QUIET)
+  set(RapidJSON_MIN_VERSION "1.1.0")
+  find_package(RapidJSON ${RapidJSON_MIN_VERSION} QUIET)
   if(NOT DEFINED RapidJSON_INCLUDE_DIRS AND DEFINED RAPIDJSON_INCLUDE_DIRS)
-    message(FATAL_ERROR "RapidJSON version is likely too old. See https://github.com/MaskRay/ccls/issues/455")
+    set(RapidJSON_INCLUDE_DIRS "${RAPIDJSON_INCLUDE_DIRS}")
   endif()
 endif()
 if(NOT RapidJSON_FOUND)
-  set(RapidJSON_INCLUDE_DIRS third_party/rapidjson/include)
+  if(EXISTS "${CMAKE_SOURCE_DIR}/third_party/rapidjson/include")
+    message(STATUS "Using local RapidJSON")
+    set(RapidJSON_INCLUDE_DIRS third_party/rapidjson/include)
+  else()
+    message(STATUS "Plase initialize rapidJSON git submodule as currently installed version is to old:")
+    message(STATUS "git submodule init && git submodule update")
+    message(FATAL_ERROR "RapidJSON version is likely too old. See https://github.com/MaskRay/ccls/issues/455")
+  endif()
 endif()
 
 target_include_directories(ccls PRIVATE src)