Add version check to Findnlohmann_json.cmake

externals/find-modules/Findnlohmann_json.cmake

@@ -8,11 +8,25 @@ find_path(nlohmann_json_INCLUDE_DIR
   PATH_SUFFIXES nlohmann
 )
 
+if(nlohmann_json_INCLUDE_DIR)
+  file(STRINGS "${nlohmann_json_INCLUDE_DIR}/json.hpp" _nlohmann_json_version_lines
+    REGEX "#define[ \t]+NLOHMANN_JSON_VERSION_(MAJOR|MINOR|PATCH)")
+  string(REGEX REPLACE ".*NLOHMANN_JSON_VERSION_MAJOR +\([0-9]+\).*" "\\1" _nlohmann_json_version_major "${_nlohmann_json_version_lines}")
+  string(REGEX REPLACE ".*NLOHMANN_JSON_VERSION_MINOR +\([0-9]+\).*" "\\1" _nlohmann_json_version_minor "${_nlohmann_json_version_lines}")
+  string(REGEX REPLACE ".*NLOHMANN_JSON_VERSION_PATCH +\([0-9]+\).*" "\\1" _nlohmann_json_version_patch "${_nlohmann_json_version_lines}")
+  set(nlohmann_json_VERSION "${_nlohmann_json_version_major}.${_nlohmann_json_version_minor}.${_nlohmann_json_version_patch}")
+  unset(_nlohmann_json_version_major)
+  unset(_nlohmann_json_version_minor)
+  unset(_nlohmann_json_version_patch)
+  unset(_nlohmann_json_version_lines)
+endif()
+
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(nlohmann_json
   FOUND_VAR nlohmann_json_FOUND
   REQUIRED_VARS
     nlohmann_json_INCLUDE_DIR
+    nlohmann_json_VERSION
   VERSION_VAR nlohmann_json_VERSION
 )