Merge pull request #7694 from sergiud:cmake-config-optional-components

cmake/templates/OpenCVConfig.cmake.in

@@ -14,6 +14,10 @@
 #
 #    find_package(OpenCV REQUIRED core videoio)
 #
+#    You can also mark OpenCV components as optional:
+
+#    find_package(OpenCV REQUIRED core OPTIONAL_COMPONENTS viz)
+#
 #    If the module is found then OPENCV_<MODULE>_FOUND is set to TRUE.
 #
 #    This file will define the following variables:
@@ -48,6 +52,21 @@ SET(OpenCV_VERSION_PATCH  @OPENCV_VERSION_PATCH@)
 SET(OpenCV_VERSION_TWEAK  0)
 SET(OpenCV_VERSION_STATUS "@OPENCV_VERSION_STATUS@")
 
+include(FindPackageHandleStandardArgs)
+
+if(NOT CMAKE_VERSION VERSION_LESS 2.8.8
+    AND OpenCV_FIND_COMPONENTS  # prevent excessive output
+)
+  # HANDLE_COMPONENTS was introduced in CMake 2.8.8
+  list(APPEND _OpenCV_FPHSA_ARGS HANDLE_COMPONENTS)
+  # The missing components will be handled by the FindPackageHandleStandardArgs
+  # module.
+  set(_OpenCV_HANDLE_COMPONENTS_MANUALLY FALSE)
+else()
+  # The missing components will be handled by this config.
+  set(_OpenCV_HANDLE_COMPONENTS_MANUALLY TRUE)
+endif()
+
 # Extract directory name from full path of the file currently being processed.
 # Note that CMake 2.8.3 introduced CMAKE_CURRENT_LIST_DIR. We reimplement it
 # for older versions of CMake to support these as well.
@@ -120,24 +139,33 @@ endif()
 set(OpenCV_WORLD_COMPONENTS @OPENCV_WORLD_MODULES@)
 
 # expand short module names and see if requested components exist
-set(OpenCV_FIND_COMPONENTS_ "")
 foreach(__cvcomponent ${OpenCV_FIND_COMPONENTS})
+  # Store the name of the original component so we can set the
+  # OpenCV_<component>_FOUND variable which can be checked by the user.
+  set (__original_cvcomponent ${__cvcomponent})
   if(NOT __cvcomponent MATCHES "^opencv_")
     set(__cvcomponent opencv_${__cvcomponent})
   endif()
   list(FIND OpenCV_LIB_COMPONENTS ${__cvcomponent} __cvcomponentIdx)
   if(__cvcomponentIdx LESS 0)
-    #requested component is not found...
-    if(OpenCV_FIND_REQUIRED)
+    if(_OpenCV_HANDLE_COMPONENTS_MANUALLY)
+      # Either the component is required or the user did not set any components at
+      # all. In the latter case, the OpenCV_FIND_REQUIRED_<component> variable
+      # will not be defined since it is not set by this config. So let's assume
+      # the implicitly set components are always required.
+      if(NOT DEFINED OpenCV_FIND_REQUIRED_${__original_cvcomponent} OR
+          OpenCV_FIND_REQUIRED_${__original_cvcomponent})
         message(FATAL_ERROR "${__cvcomponent} is required but was not found")
       elseif(NOT OpenCV_FIND_QUIETLY)
-      message(WARNING "${__cvcomponent} is required but was not found")
+        # The component was marked as optional using OPTIONAL_COMPONENTS
+        message(WARNING "Optional component ${__cvcomponent} was not found")
       endif()
+    endif(_OpenCV_HANDLE_COMPONENTS_MANUALLY)
     #indicate that module is NOT found
     string(TOUPPER "${__cvcomponent}" __cvcomponentUP)
     set(${__cvcomponentUP}_FOUND "${__cvcomponentUP}_FOUND-NOTFOUND")
+    set(OpenCV_${__original_cvcomponent}_FOUND FALSE)
   else()
-    list(APPEND OpenCV_FIND_COMPONENTS_ ${__cvcomponent})
     # Not using list(APPEND) here, because OpenCV_LIBS may not exist yet.
     # Also not clearing OpenCV_LIBS anywhere, so that multiple calls
     # to find_package(OpenCV) with different component lists add up.
@@ -145,6 +173,7 @@ foreach(__cvcomponent ${OpenCV_FIND_COMPONENTS})
     #indicate that module is found
     string(TOUPPER "${__cvcomponent}" __cvcomponentUP)
     set(${__cvcomponentUP}_FOUND 1)
+    set(OpenCV_${__original_cvcomponent}_FOUND TRUE)
   endif()
   if(OpenCV_SHARED AND ";${OpenCV_WORLD_COMPONENTS};" MATCHES ";${__cvcomponent};" AND NOT TARGET ${__cvcomponent})
     get_target_property(__implib_dbg opencv_world IMPORTED_IMPLIB_DEBUG)
@@ -170,7 +199,6 @@ foreach(__cvcomponent ${OpenCV_FIND_COMPONENTS})
     endif()
   endif()
 endforeach()
-set(OpenCV_FIND_COMPONENTS ${OpenCV_FIND_COMPONENTS_})
 
 # ==============================================================
 # Compatibility stuff
@@ -226,3 +254,8 @@ macro(ocv_list_filterout lst regex)
     endif()
   endforeach()
 endmacro()
+
+# We do not actually need REQUIRED_VARS to be checked for. Just use the
+# installation directory for the status.
+find_package_handle_standard_args(OpenCV REQUIRED_VARS OpenCV_INSTALL_PATH
+                                  VERSION_VAR OpenCV_VERSION ${_OpenCV_FPHSA_ARGS})