Merge pull request #5195 from mshabunin:warn-missing-contrib

cmake/OpenCVModule.cmake

@@ -248,7 +248,7 @@ macro(ocv_glob_modules)
   foreach(__path ${ARGN})
     if("${__path}" STREQUAL "EXTRA")
       set(OPENCV_PROCESSING_EXTRA_MODULES 1)
-    endif()
+    else()
       get_filename_component(__path "${__path}" ABSOLUTE)
 
       list(FIND __directories_observed "${__path}" __pathIdx)
@@ -257,6 +257,7 @@ macro(ocv_glob_modules)
       endif()
       list(APPEND __directories_observed "${__path}")
 
+      set(__count 0)
       file(GLOB __ocvmodules RELATIVE "${__path}" "${__path}/*")
       if(__ocvmodules)
         list(SORT __ocvmodules)
@@ -271,9 +272,17 @@ macro(ocv_glob_modules)
             list(APPEND __directories_observed "${__modpath}")
 
             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)