[CMake] find_package REQUIRED ignores OPTIONAL_COMPONENTS

[Alexander Stein]

Hi,

I want to use some required Qt component while others are optional. Apparently if you specify REQUIRED in find_package OPTIONAL_COMPONENTS is ignored.
Here is a minimal CMakeLists.txt:
project(test)
cmake_minimum_required(VERSION 3.5)

find_package(Qt4 REQUIRED COMPONENTS QtCore QtGui OPTIONAL_COMPONENTS Invalid)

/home/alex/repo/cmake/build/bin/cmake --version
cmake version 3.5.20160303-gf37f

cmake fails with:
CMake Error at /home/alex/repo/cmake/Modules/FindPackageHandleStandardArgs.cmake:148 (message):
  Could NOT find Qt4 (missing: QT_INVALID_INCLUDE_DIR QT_INVALID_LIBRARY)
  (found version "4.8.7")
Call Stack (most recent call first):
  /home/alex/repo/cmake/Modules/FindPackageHandleStandardArgs.cmake:388 (_FPHSA_FAILURE_MESSAGE)
  /home/alex/repo/cmake/Modules/FindQt4.cmake:1333 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  CMakeLists.txt:4 (find_package)

I expected that if required components are missing cmake bails out while continuing when OPTIONAL_COMPONENTS are missing. My current workaround is:
find_package(Qt4 OPTIONAL_COMPONENTS Invalid)
find_package(Qt4 REQUIRED COMPONENTS QtCore QtGui)

But I would rather use a single line. Am I missing something here?

Best regards,
Alexander