cmake: Added missing extra modules warning

cmake/OpenCVModule.cmake

@@ -248,31 +248,40 @@ macro(ocv_glob_modules)
   foreach(__path ${ARGN})
     if("${__path}" STREQUAL "EXTRA")
       set(OPENCV_PROCESSING_EXTRA_MODULES 1)
-    endif()
-    get_filename_component(__path "${__path}" ABSOLUTE)
+    else()
+      get_filename_component(__path "${__path}" ABSOLUTE)
 
-    list(FIND __directories_observed "${__path}" __pathIdx)
-    if(__pathIdx GREATER -1)
-      message(FATAL_ERROR "The directory ${__path} is observed for OpenCV modules second time.")
-    endif()
-    list(APPEND __directories_observed "${__path}")
-
-    file(GLOB __ocvmodules RELATIVE "${__path}" "${__path}/*")
-    if(__ocvmodules)
-      list(SORT __ocvmodules)
-      foreach(mod ${__ocvmodules})
-        get_filename_component(__modpath "${__path}/${mod}" ABSOLUTE)
-        if(EXISTS "${__modpath}/CMakeLists.txt")
-
-          list(FIND __directories_observed "${__modpath}" __pathIdx)
-          if(__pathIdx GREATER -1)
-            message(FATAL_ERROR "The module from ${__modpath} is already loaded.")
-          endif()
-          list(APPEND __directories_observed "${__modpath}")
+      list(FIND __directories_observed "${__path}" __pathIdx)
+      if(__pathIdx GREATER -1)
+        message(FATAL_ERROR "The directory ${__path} is observed for OpenCV modules second time.")
+      endif()
+      list(APPEND __directories_observed "${__path}")
+
+      set(__count 0)
+      file(GLOB __ocvmodules RELATIVE "${__path}" "${__path}/*")
+      if(__ocvmodules)
+        list(SORT __ocvmodules)
+        foreach(mod ${__ocvmodules})
+          get_filename_component(__modpath "${__path}/${mod}" ABSOLUTE)
+          if(EXISTS "${__modpath}/CMakeLists.txt")
+
+            list(FIND __directories_observed "${__modpath}" __pathIdx)
+            if(__pathIdx GREATER -1)
+              message(FATAL_ERROR "The module from ${__modpath} is already loaded.")
+            endif()
+            list(APPEND __directories_observed "${__modpath}")
 
-          add_subdirectory("${__modpath}" "${CMAKE_CURRENT_BINARY_DIR}/${mod}/.${mod}")
-        endif()
-      endforeach()
+            add_subdirectory("${__modpath}" "${CMAKE_CURRENT_BINARY_DIR}/${mod}/.${mod}")
+
+            if (DEFINED OPENCV_MODULE_opencv_${mod}_LOCATION)
+              math(EXPR __count "${__count} + 1")
+            endif()
+          endif()
+        endforeach()
+      endif()
+      if (OPENCV_PROCESSING_EXTRA_MODULES AND ${__count} LESS 1)
+        message(SEND_ERROR "No extra modules found in folder: ${__path}\nPlease provide path to 'opencv_contrib/modules' folder.")
+      endif()
     endif()
   endforeach()
   ocv_clear_vars(__ocvmodules __directories_observed __path __modpath __pathIdx)