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.

ultrastardx fails because its autoconf configure script only ever
probes pkg-config for "opencv4" and the bare "opencv" module name
(build log: "checking for OpenCV... no" / "checking for opencv4...
no" / "checking for opencv >= 3.0.0... no", followed by the fatal
"configure: error: OpenCV was requested but not found" at log line
3830). The --with-opencv-cxx-api configure run therefore aborts
before any compilation happens, and the override_dh_auto_configure
rule fails with exit code 25 (make[1]: *** [debian/rules:17:
override_dh_auto_configure] Error 25). The maintainer should extend
configure.ac's OpenCV pkg-config probe to also try "opencv5" (e.g.
PKG_CHECK_MODULES trying opencv5 before falling back to
opencv4/opencv), regenerating configure with the change.

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.

  checking for a sed that does not truncate output... /usr/bin/sed
  checking for grep that handles long lines and -e... /usr/bin/grep
  checking for cmake... no
  checking build system type... x86_64-pc-linux-gnu
  checking host system type... x86_64-pc-linux-gnu
  checking for fpc... fpc
  checking for fpcmake... fpcmake
  checking version of fpc... [3.2.2]
  checking whether the Free Pascal Compiler works... yes
  checking whether the Free Pascal Compiler can link... yes
  checking whether FPC supports -k"-z noexecstack"... yes
  checking whether FPC supports -k"--copy-dt-needed-entries"... yes
  checking for gcc... x86_64-linux-gnu-gcc
  checking whether the C compiler works... yes
  checking for C compiler default output file name... a.out
  checking for suffix of executables...
  checking whether we are cross compiling... no
  checking for suffix of object files... o
  checking whether the compiler supports GNU C... yes
  checking whether x86_64-linux-gnu-gcc accepts -g... yes
  checking for x86_64-linux-gnu-gcc option to enable C23 features... none needed
  checking for ranlib... ranlib
  checking for pkg-config... /usr/bin/pkg-config
  checking pkg-config is at least version 0.9.0... yes
  checking for sdl2... yes
  checking for SDL2_image... yes
  checking for freetype2... yes
  checking for sqlite3... yes
  checking for lua5.5... no
  checking for lua5.4... no
  checking for lua5.3... yes
  checking version of lua... [5.3.6]
  checking size of lua_Integer... 64 bits
  checking for library containing luaL_newstate... -llua5.3
  checking for libavcodec... yes
  checking version of libavcodec... [62.28.102]
  checking for libavformat... yes
  checking version of libavformat... [62.12.102]
  checking for libavutil... yes
  checking version of libavutil... [60.26.102]
  checking for libswscale... yes
  checking version of libswscale... [9.5.102]
  checking for libswresample... yes
  checking version of libswresample... [6.3.102]
  checking version of ffmpeg... [8.0]
  configure: Checking for C++ compiler
  checking whether the compiler supports GNU C++... yes
  checking whether x86_64-linux-gnu-g++ accepts -g... yes
  checking if C++ toolchain works... yes
  checking for libprojectM >= 1.0... no
  checking whether x86_64-linux-gnu-g++ supports C++11 features with
-std=gnu++11... yes
  checking for OpenCV... no
  checking for opencv4... no
  checking for opencv >= 3.0.0... no
  configure: error: in '/build/reproducible-path/ultrastardx-2026.6.0+dfsg2':
  configure: error: OpenCV was requested but not found

Please close this bug if it turns out to be a collision with another ongoing
transition rather than an OpenCV 5 problem.

Thanks,
Aron