find_package in vcpkg.cmake must honor CMAKE_DISABLE_FIND_PACKAGE_<NAME>

[dg0yt]

Describe the bug

In pristine CMake, "every non-REQUIRED find_package() call in a project can be disabled by setting the variable CMAKE_DISABLE_FIND_PACKAGE_<PackageName> to TRUE." This means, there are no side effects.

vcpkg.cmake overrides cmake's original find_package. It always includes vcpkg-cmake-wrapper.cmake for <PackageName> if it exists:

vcpkg/scripts/buildsystems/vcpkg.cmake

Lines 716 to 725 in 876e67c

	if(EXISTS "${z_vcpkg_find_package_vcpkg_cmake_wrapper_path}")
	list(APPEND z_vcpkg_find_package_backup_vars "ARGS")
	if(DEFINED ARGS)
	set(z_vcpkg_find_package_backup_ARGS "${ARGS}")
	else()
	set(z_vcpkg_find_package_backup_ARGS)
	endif()
	set(ARGS "${z_vcpkg_find_package_package_name};${z_vcpkg_find_package_ARGN}")
	include("${z_vcpkg_find_package_vcpkg_cmake_wrapper_path}")

So all side effects from the wrapper always occur, e.g. failures to load transitive dependencies.

Actual behaviour:
An example of the actual behaviour is seen in current simage build errors for osx: The simage build system is configured with -DCMAKE_DISABLE_FIND_PACKAGE_TIFF=ON. Still, iff port tiff happens to be already installed (and quicktime is not available), the wrapper for TIFF is loaded, and it causes an configuration error because the dependencies of TIFF (JPEG, ZLIB) are disabled, too:

-- Configuring x64-osx-dbg
CMake Error at scripts/cmake/vcpkg_execute_required_process.cmake:105 (message):
    Command failed: /Users/vagrant/Data/downloads/tools/cmake-3.20.2-osx/cmake-3.20.2-macos-universal/CMake.app/Contents/bin/cmake /Users/vagrant/Data/buildtrees/simage/src/mage-1.8.0-17f988a113.clean -DSIMAGE_BUILD_SHARED_LIBS=OFF -DSIMAGE_USE_AVIENC=OFF -DSIMAGE_USE_GDIPLUS=OFF -DCMAKE_DISABLE_FIND_PACKAGE_FLAC=ON -DCMAKE_DISABLE_FIND_PACKAGE_Jasper=ON -DCMAKE_DISABLE_FIND_PACKAGE_Doxygen=ON -DCMAKE_DISABLE_FIND_PACKAGE_ZLIB=ON -DCMAKE_DISABLE_FIND_PACKAGE_GIF=ON -DCMAKE_DISABLE_FIND_PACKAGE_JPEG=ON -DCMAKE_DISABLE_FIND_PACKAGE_PNG=ON -DCMAKE_DISABLE_FIND_PACKAGE_TIFF=ON -DCMAKE_MAKE_PROGRAM=/Users/vagrant/Data/downloads/tools/ninja-1.10.2-osx/ninja -DCMAKE_SYSTEM_NAME=Darwin -DBUILD_SHARED_LIBS=OFF -DVCPKG_CHAINLOAD_TOOLCHAIN_FILE=/Users/vagrant/Data/work/1/s/scripts/toolchains/osx.cmake -DVCPKG_TARGET_TRIPLET=x64-osx -DVCPKG_SET_CHARSET_FLAG=ON -DVCPKG_PLATFORM_TOOLSET=external -DCMAKE_EXPORT_NO_PACKAGE_REGISTRY=ON -DCMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY=ON -DCMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY=ON -DCMAKE_INSTALL_SYSTEM_RUNTIME_LIBS_SKIP=TRUE -DCMAKE_VERBOSE_MAKEFILE=ON -DVCPKG_APPLOCAL_DEPS=OFF -DCMAKE_TOOLCHAIN_FILE=/Users/vagrant/Data/work/1/s/scripts/buildsystems/vcpkg.cmake -DCMAKE_ERROR_ON_ABSOLUTE_INSTALL_DESTINATION=ON -DVCPKG_CXX_FLAGS= -DVCPKG_CXX_FLAGS_RELEASE= -DVCPKG_CXX_FLAGS_DEBUG= -DVCPKG_C_FLAGS= -DVCPKG_C_FLAGS_RELEASE= -DVCPKG_C_FLAGS_DEBUG= -DVCPKG_CRT_LINKAGE=dynamic -DVCPKG_LINKER_FLAGS= -DVCPKG_LINKER_FLAGS_RELEASE= -DVCPKG_LINKER_FLAGS_DEBUG= -DVCPKG_TARGET_ARCHITECTURE=x64 -DCMAKE_INSTALL_LIBDIR:STRING=lib -DCMAKE_INSTALL_BINDIR:STRING=bin -D_VCPKG_ROOT_DIR=/Users/vagrant/Data/work/1/s -D_VCPKG_INSTALLED_DIR=/Users/vagrant/Data/installed -DVCPKG_MANIFEST_INSTALL=OFF -DCMAKE_OSX_ARCHITECTURES=x86_64 -G Ninja -DCMAKE_BUILD_TYPE=Debug -DCMAKE_INSTALL_PREFIX=/Users/vagrant/Data/packages/simage_x64-osx/debug

CMake Error at /Users/vagrant/Data/installed/x64-osx/share/jpeg/vcpkg-cmake-wrapper.cmake:1 (_find_package):
  _find_package for module JPEG called with REQUIRED, but
  CMAKE_DISABLE_FIND_PACKAGE_JPEG is enabled.  A REQUIRED package cannot be
  disabled.
Call Stack (most recent call first):
  /Users/vagrant/Data/work/1/s/scripts/buildsystems/vcpkg.cmake:745 (include)
  /Users/vagrant/Data/installed/x64-osx/share/tiff/vcpkg-cmake-wrapper.cmake:17 (find_package)
  /Users/vagrant/Data/work/1/s/scripts/buildsystems/vcpkg.cmake:745 (include)
  CMakeLists.txt:222 (find_package)


CMake Error at /Users/vagrant/Data/work/1/s/scripts/buildsystems/vcpkg.cmake:791 (_find_package):
  _find_package for module ZLIB called with REQUIRED, but
  CMAKE_DISABLE_FIND_PACKAGE_ZLIB is enabled.  A REQUIRED package cannot be
  disabled.

(From #18393 (comment))

Expected behavior:
For consistency with CMake, no side effects are allowed for non-REQUIRED find_package() calls when the variable CMAKE_DISABLE_FIND_PACKAGE_<PackageName> is set to TRUE, i.e. find_package must return early, without loading wrappers.

In the simage example, the TIFF wrapper must not be loaded for the find_package(TIFF) call in simage's CMakeLists.txt, due to
CMAKE_DISABLE_FIND_PACKAGE_TIFF being set.

[dg0yt]

Expected behavior:
For consistency with CMake, no side effects are allowed for non-REQUIRED find_package() calls when the variable CMAKE_DISABLE_FIND_PACKAGE_<PackageName> is set to TRUE, i.e. find_package must return early, without loading wrappers.

Plus: For REQUIRED calls, find_package in vcpkg.cmake must fail early.

[ras0219-msft]

Yes, this is definitely a bug

[dg0yt]

Fixed by #18961.

[JackBoosY]

Please keep this issue open until #18961 merged.