Dear maintainer,

Your package fails to build from source against opencv 5.0.0+dfsg-1~exp1,
currently in experimental.

OpenCV 5.0 renames its entire install tree from opencv4 to opencv5 and ships
no compatibility shims:

  * pkg-config: only /usr/lib/<triplet>/pkgconfig/opencv5.pc.  There is no
                opencv4.pc and no opencv.pc.
  * headers:    /usr/include/opencv5/opencv2/..., no /usr/include/opencv4.
  * cmake:      /usr/lib/<triplet>/cmake/opencv5/OpenCVConfig.cmake.  A bare
                find_package(OpenCV) still resolves, but a pinned version
                such as find_package(OpenCV 4.7) no longer matches.
  * modules:    libopencv-calib3d-dev is split into libopencv-calib-dev,
                libopencv-geometry-dev, libopencv-stereo-dev and
                libopencv-ptcloud-dev; libopencv-features2d-dev becomes
                libopencv-features-dev.  The CMake component names change
                with them (features2d -> features).
  * geometry:   the new geometry module is not only a piece of calib3d.  It
                also absorbs shape and contour functions that used to live
                in imgproc -- contourArea, arcLength, approxPolyDP,
                boundingRect, minAreaRect, convexHull and
                getPerspectiveTransform among them -- and opencv2/opencv.hpp
                does not pull in opencv2/geometry.hpp, so code that reached
                those through the umbrella header now needs an explicit
                include of opencv2/geometry.hpp.

In kde-spectacle's case, CMakeLists.txt:94 calls find_package(OpenCV 4.7)
(or similarly pins a 4.x floor), and CMake's config-mode search rejects
the only OpenCV package present, /usr/lib/x86_64-linux-gnu/cmake/opencv5/
OpenCVConfig.cmake, because it reports version 5.0.0, which does not
satisfy the requested "4.7" constraint. The log shows this is a plain
version mismatch, not a missing package or a moved component: OpenCV is
found, just refused on version grounds. The maintainer should update
CMakeLists.txt:94 to accept OpenCV 5 (e.g. find_package(OpenCV 5) or a
version range covering 4.7..<6), and audit the OpenCV modules the
project actually links against for the calib3d/features2d renames noted
above.

The same source builds fine in the same chroot against the OpenCV 4.10
packages currently in unstable, so this is specific to OpenCV 5.

The relevant part of the build log follows; the full log is attached.