Handle OPTIONAL_COMPONENTS in find_package(YARP)

There is no way to make this work with `find_dependency()` since it
passes caller's REQUIRED to the underlying `find_package()` call.
That is, no error should be raised if an optional component was not
found while issuing a `find_package(YARP REQUIRED ...)` command.

cmake/template/YARPConfig.cmake.in

@@ -7,7 +7,6 @@
 
 
 
-include(CMakeFindDependencyMacro)
 include(CMakeDependentOption)
 
 
@@ -116,17 +115,14 @@ set(YARP_QML2_IMPORT_DIR_FULL "@PACKAGE_YARP_QML2_IMPORT_DIR@")
 # Used by YarpIDL.cmake
 set(YARP_IDL_BINARY_HINT "@PACKAGE_YARP_IDL_BINARY_HINT@")
 
-# FIXME Remove this check when CMake 3.9 or later is required
-#       This is used later and in YARPTargetsStatic.cmake
-if (CMAKE_VERSION VERSION_LESS 3.9)
-  set(_YARP_FIND_PARTS_REQUIRED)
-  if (YARP_FIND_REQUIRED)
-    set(_YARP_FIND_PARTS_REQUIRED REQUIRED)
-  endif()
-  set(_YARP_FIND_PARTS_QUIET)
-  if (YARP_FIND_QUIETLY)
-    set(_YARP_FIND_PARTS_QUIET QUIET)
-  endif()
+# This is used later and in YARPTargetsStatic.cmake
+set(_YARP_FIND_PARTS_REQUIRED)
+if (YARP_FIND_REQUIRED)
+  set(_YARP_FIND_PARTS_REQUIRED REQUIRED)
+endif()
+set(_YARP_FIND_PARTS_QUIET)
+if (YARP_FIND_QUIETLY)
+  set(_YARP_FIND_PARTS_QUIET QUIET)
 endif()
 
 # Include YARPTargets.cmake file (that includes for now, targets without a
@@ -149,19 +145,19 @@ endif()
 # Find all requested components
 set(YARP_LIBRARIES YARP::YARP_init)
 foreach(_yarp_module ${YARP_FIND_COMPONENTS})
-  # FIXME Remove this check when CMake 3.9 or later is required
-  if (CMAKE_VERSION VERSION_LESS 3.9)
-    find_package(YARP_${_yarp_module}
-                 ${_YARP_FIND_PARTS_QUIET}
-                 ${_YARP_FIND_PARTS_REQUIRED}
-                 HINTS "${YARP_CMAKECONFIG_DIR}"
-                 NO_DEFAULT_PATH)
-  else()
-    find_dependency(YARP_${_yarp_module}
-                    HINTS "${YARP_CMAKECONFIG_DIR}"
-                    NO_DEFAULT_PATH)
+  set(_YARP_FIND_PART_${_yarp_module}_REQUIRED)
+  # Only propagate REQUIRED if module was not passed to OPTIONAL_COMPONENTS
+  if(YARP_FIND_REQUIRED_${_yarp_module})
+    set(_YARP_FIND_PART_${_yarp_module}_REQUIRED ${_YARP_FIND_PARTS_REQUIRED})
+  endif()
+  find_package(YARP_${_yarp_module}
+               ${_YARP_FIND_PARTS_QUIET}
+               ${_YARP_FIND_PART_${_yarp_module}_REQUIRED}
+               HINTS "${YARP_CMAKECONFIG_DIR}"
+               NO_DEFAULT_PATH)
+  if(YARP_${_yarp_module}_FOUND)
+    list(APPEND YARP_LIBRARIES YARP::YARP_${_yarp_module})
   endif()
-  list(APPEND YARP_LIBRARIES YARP::YARP_${_yarp_module})
 endforeach()
 
 # Ensure that all requested modules are available

cmake/template/YARPTargetsStatic.cmake.in

@@ -41,18 +41,17 @@ list(APPEND CMAKE_MODULE_PATH ${YARP_MODULE_PATH})
 # Properly find the dependencies. This will force to include all the
 # dependencies also for packages in other exports
 foreach(_target ${_targets})
-  # FIXME Remove this check when CMake 3.9 or later is required
-  if (CMAKE_VERSION VERSION_LESS 3.9)
-    find_package(${_target}
-                 ${_YARP_FIND_PARTS_QUIET}
-                 ${_YARP_FIND_PARTS_REQUIRED}
-                 HINTS "${YARP_CMAKECONFIG_DIR}"
-                 NO_DEFAULT_PATH)
-  else()
-    find_dependency(${_target}
-                    HINTS "${YARP_CMAKECONFIG_DIR}"
-                    NO_DEFAULT_PATH)
+  string(REGEX REPLACE "^YARP_" "" _target "${_target}")
+  set(_YARP_FIND_PART_${_target}_REQUIRED)
+  # Only propagate REQUIRED if module was not passed to OPTIONAL_COMPONENTS
+  if(YARP_FIND_REQUIRED_${_target})
+    set(_YARP_FIND_PART_${_target}_REQUIRED ${_YARP_FIND_PARTS_REQUIRED})
   endif()
+  find_package(YARP_${_target}
+               ${_YARP_FIND_PARTS_QUIET}
+               ${_YARP_FIND_PART_${_target}_REQUIRED}
+               HINTS "${YARP_CMAKECONFIG_DIR}"
+               NO_DEFAULT_PATH)
 endforeach()
 
 # Restore the original situation

doc/release/v3_1_0.md

@@ -8,6 +8,10 @@ A (partial) list of bug fixed and issues resolved in this release can be found
 New Features
 ------------
 
+### Build System
+
+* Added support for `OPTIONAL_COMPONENTS` in `find_package(YARP)` calls.
+
 ### Devices
 
 #### imuBosch_BNO055