Issue 1:
System information (version)

OpenCV => 4

Operating System / Platform => Ubuntu 16.04

Detailed description

Looks like I have an issue to capture image from a camera, e.g. running example_cpp_videocapture_camera returns the following error:

Opening camera...

[ WARN:0] VideoCapture(index=0) was built without support of requested backendID=200

ERROR: Can't initialize camera capture

There is no issue with latest OpenCV 3.4 branch (93d1785).

My configuration:

General configuration for OpenCV 4.0.0-pre =====================================
Version control: 3.4.3-844-g5459c11

Platform:
Timestamp: 2018-11-12T15:48:29Z
Host: Linux 4.4.0-138-generic x86_64
CMake: 3.5.1
CMake generator: Unix Makefiles
CMake build tool: /usr/bin/make
Configuration: Release

CPU/HW features:
Baseline: SSE SSE2 SSE3
requested: SSE3
Dispatched code generation: SSE4_1 SSE4_2 FP16 AVX AVX2 AVX512_SKX
requested: SSE4_1 SSE4_2 AVX FP16 AVX2 AVX512_SKX
SSE4_1 (4 files): + SSSE3 SSE4_1
SSE4_2 (1 files): + SSSE3 SSE4_1 POPCNT SSE4_2
FP16 (0 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 AVX
AVX (4 files): + SSSE3 SSE4_1 POPCNT SSE4_2 AVX
AVX2 (10 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2
AVX512_SKX (1 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2 AVX_512F AVX512_SKX

C/C++:
Built as dynamic libs?: YES
C++ Compiler: /usr/bin/c++ (ver 5.4.0)
C++ flags (Release): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
C++ flags (Debug): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
C Compiler: /usr/bin/cc
C flags (Release): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-narrowing -Wno-comment -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -O3 -DNDEBUG -DNDEBUG
C flags (Debug): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-narrowing -Wno-comment -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -g -O0 -DDEBUG -D_DEBUG
Linker flags (Release):
Linker flags (Debug):
ccache: NO
Precompiled headers: YES
Extra dependencies: dl m pthread rt
3rdparty dependencies:

OpenCV modules:
To be built: calib3d core dnn features2d flann gapi highgui imgcodecs imgproc java java_bindings_generator ml objdetect photo python2 python3 python_bindings_generator stitching ts video videoio
Disabled: world
Disabled by dependency: -
Unavailable: js
Applications: examples apps
Documentation: NO
Non-free algorithms: NO

GUI:
GTK+: YES (ver 3.18.9)
GThread : YES (ver 2.48.2)
GtkGlExt: NO
VTK support: YES (ver 6.2.0)

Media I/O:
ZLib: /usr/lib/x86_64-linux-gnu/libz.so (ver 1.2.8)
JPEG: /usr/lib/x86_64-linux-gnu/libjpeg.so (ver 80)
WEBP: /usr/lib/x86_64-linux-gnu/libwebp.so (ver encoder: 0x0202)
PNG: /usr/lib/x86_64-linux-gnu/libpng.so (ver 1.2.54)
TIFF: /usr/lib/x86_64-linux-gnu/libtiff.so (ver 42 / 4.0.6)
JPEG 2000: /usr/lib/x86_64-linux-gnu/libjasper.so (ver 1.900.1)
OpenEXR: /usr/lib/x86_64-linux-gnu/libImath.so /usr/lib/x86_64-linux-gnu/libIlmImf.so /usr/lib/x86_64-linux-gnu/libIex.so /usr/lib/x86_64-linux-gnu/libHalf.so /usr/lib/x86_64-linux-gnu/libIlmThread.so (ver 2.2.0)
HDR: YES
SUNRASTER: YES
PXM: YES
PFM: YES

Video I/O:
DC1394: YES (ver 2.2.4)
FFMPEG: YES
avcodec: YES (ver 56.60.100)
avformat: YES (ver 56.40.101)
avutil: YES (ver 54.31.100)
swscale: YES (ver 3.1.101)
avresample: NO
GStreamer: NO
libv4l/libv4l2: NO
v4l/v4l2: linux/videodev2.h

Parallel framework: pthreads

Trace: YES (with Intel ITT)

Other third-party libraries:
Intel IPP: 2019.0.0 Gold [2019.0.0]
at: /home/user/opencv-build/3rdparty/ippicv/ippicv_lnx/icv
Intel IPP IW: sources (2019.0.0)
at: /home/user/opencv-build/3rdparty/ippicv/ippicv_lnx/iw
Lapack: YES (/opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_intel_lp64.so /opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_sequential.so /opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_core.so /opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_intel_lp64.so /opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_sequential.so /opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_core.so /opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_intel_lp64.so /opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_sequential.so /opt/intel/compilers_and_libraries_2017.4.196/linux/mkl/lib/intel64/libmkl_core.so -lpthread -lm -ldl)
Eigen: YES (ver 3.2.92)
Custom HAL: NO
Protobuf: build (3.5.1)

OpenCL: YES (no extra features)
Include path: /home/user/opencv/opencv-fork/3rdparty/include/opencl/1.2
Link libraries: Dynamic load

Python 2:
Interpreter: /usr/bin/python2.7 (ver 2.7.12)
Libraries: /usr/lib/x86_64-linux-gnu/libpython2.7.so (ver 2.7.12)
numpy: /usr/local/lib/python2.7/dist-packages/numpy/core/include (ver 1.12.0)
packages path: lib/python2.7/dist-packages

Python 3:
Interpreter: /usr/bin/python3 (ver 3.5.2)
Libraries: /usr/lib/x86_64-linux-gnu/libpython3.5m.so (ver 3.5.2)
numpy: /usr/lib/python3/dist-packages/numpy/core/include (ver 1.11.0)
packages path: lib/python3.5/dist-packages

Python (for build): /usr/bin/python2.7

Java:
ant: /usr/bin/ant (ver 1.9.6)
JNI: /usr/lib/jvm/default-java/include /usr/lib/jvm/default-java/include/linux /usr/lib/jvm/default-java/include
Java wrappers: YES
Java tests: NO

Install to: /home/user/opencv-build/install
-----------------------------------------------------------------

Issue 2:
On fedora 26 I have this error when compiling openCV with the modules:

[ 84%] Building CXX object modules/optflow/CMakeFiles/opencv_perf_optflow.dir/perf/perf_main.cpp.o
[ 84%] Building CXX object modules/optflow/CMakeFiles/opencv_perf_optflow.dir/perf/perf_variational_refinement.cpp.o
In file included from /home/malcolm/external_sources/opencv/modules/python/src2/cv2.cpp:1496:0:
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h: In function ‘PyObject* pyopencv_cv_structured_light_structured_light_StructuredLightPattern_decode(PyObject*, PyObject*, PyObject*)’:
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h:45897:5: error: ‘vector_vector_Mat’ was not declared in this scope
vector_vector_Mat patternImages;
^~~~~~~~~~~~~~~~~
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h:45897:5: note: suggested alternative: ‘vector_vector_DMatch’
vector_vector_Mat patternImages;
^~~~~~~~~~~~~~~~~
vector_vector_DMatch
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h:45909:42: error: ‘patternImages’ was not declared in this scope
pyopencv_to(pyobj_patternImages, patternImages, ArgInfo("patternImages", 0)) &&
^~~~~~~~~~~~~
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h:45909:42: note: suggested alternative: ‘whiteImages’
pyopencv_to(pyobj_patternImages, patternImages, ArgInfo("patternImages", 0)) &&
^~~~~~~~~~~~~
whiteImages
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h:45922:5: error: ‘vector_vector_Mat’ was not declared in this scope
vector_vector_Mat patternImages;
^~~~~~~~~~~~~~~~~
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h:45922:5: note: suggested alternative: ‘vector_vector_DMatch’
vector_vector_Mat patternImages;
^~~~~~~~~~~~~~~~~
vector_vector_DMatch
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h:45934:42: error: ‘patternImages’ was not declared in this scope
pyopencv_to(pyobj_patternImages, patternImages, ArgInfo("patternImages", 0)) &&
^~~~~~~~~~~~~
/home/malcolm/external_sources/opencv/build/modules/python2/pyopencv_generated_types.h:45934:42: note: suggested alternative: ‘whiteImages’
pyopencv_to(pyobj_patternImages, patternImages, ArgInfo("patternImages", 0)) &&
^~~~~~~~~~~~~
whiteImages
In file included from /home/malcolm/external_sources/opencv/modules/python/src2/cv2.cpp:1496:0:
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h: In function ‘PyObject* pyopencv_cv_structured_light_structured_light_StructuredLightPattern_decode(PyObject*, PyObject*, PyObject*)’:
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h:45676:5: error: ‘vector_vector_Mat’ was not declared in this scope
vector_vector_Mat patternImages;
^~~~~~~~~~~~~~~~~
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h:45676:5: note: suggested alternative: ‘vector_vector_DMatch’
vector_vector_Mat patternImages;
^~~~~~~~~~~~~~~~~
vector_vector_DMatch
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h:45688:42: error: ‘patternImages’ was not declared in this scope
pyopencv_to(pyobj_patternImages, patternImages, ArgInfo("patternImages", 0)) &&
^~~~~~~~~~~~~
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h:45688:42: note: suggested alternative: ‘whiteImages’
pyopencv_to(pyobj_patternImages, patternImages, ArgInfo("patternImages", 0)) &&
^~~~~~~~~~~~~
whiteImages
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h:45701:5: error: ‘vector_vector_Mat’ was not declared in this scope
vector_vector_Mat patternImages;
^~~~~~~~~~~~~~~~~
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h:45701:5: note: suggested alternative: ‘vector_vector_DMatch’
vector_vector_Mat patternImages;
^~~~~~~~~~~~~~~~~
vector_vector_DMatch
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h:45713:42: error: ‘patternImages’ was not declared in this scope
pyopencv_to(pyobj_patternImages, patternImages, ArgInfo("patternImages", 0)) &&
^~~~~~~~~~~~~
/home/malcolm/external_sources/opencv/build/modules/python3/pyopencv_generated_types.h:45713:42: note: suggested alternative: ‘whiteImages’
pyopencv_to(pyobj_patternImages, patternImages, ArgInfo("patternImages", 0)) &&
^~~~~~~~~~~~~
whiteImages
[ 84%] Building CXX object modules/stitching/CMakeFiles/opencv_perf_stitching.dir/perf/perf_stich.cpp.o
[ 84%] Linking CXX executable ../../bin/opencv_perf_optflow
[ 84%] Built target opencv_perf_optflow
Scanning dependencies of target tutorial_hull_demo
[ 84%] Building CXX object samples/cpp/CMakeFiles/tutorial_hull_demo.dir/tutorial_code/ShapeDescriptors/hull_demo.cpp.o
[ 84%] Linking CXX executable ../../bin/cpp-tutorial-hull_demo
[ 84%] Built target tutorial_hull_demo
Scanning dependencies of target tutorial_EqualizeHist_Demo
[ 84%] Building CXX object samples/cpp/CMakeFiles/tutorial_EqualizeHist_Demo.dir/tutorial_code/Histograms_Matching/EqualizeHist_Demo.cpp.o
make[2]: *** [modules/python2/CMakeFiles/opencv_python2.dir/build.make:324: modules/python2/CMakeFiles/opencv_python2.dir/__/src2/cv2.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:21101: modules/python2/CMakeFiles/opencv_python2.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....
[ 84%] Linking CXX executable ../../bin/opencv_perf_stitching
[ 84%] Linking CXX executable ../../bin/cpp-tutorial-EqualizeHist_Demo
[ 84%] Built target opencv_perf_stitching
[ 84%] Built target tutorial_EqualizeHist_Demo
make[2]: *** [modules/python3/CMakeFiles/opencv_python3.dir/build.make:324: modules/python3/CMakeFiles/opencv_python3.dir/__/src2/cv2.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:21232: modules/python3/CMakeFiles/opencv_python3.dir/all] Error 2
make: *** [Makefile:163: all] Error 2

My Cmake config is as follow

General configuration for OpenCV 3.3.0-dev =====================================
-- Version control: 3.3.0-370-g7475d23fe
--
-- Extra modules:
-- Location (extra): /home/malcolm/external_sources/opencv_contrib/modules
-- Version control (extra): 3.3.0-58-g4bc49c05
--
-- Platform:
-- Timestamp: 2017-09-26T18:52:28Z
-- Host: Linux 4.12.9-300.fc26.x86_64 x86_64
-- CMake: 3.9.1
-- CMake generator: Unix Makefiles
-- CMake build tool: /usr/bin/gmake
-- Configuration: Release
--
-- CPU/HW features:
-- Baseline: SSE SSE2 SSE3
-- requested: SSE3
-- Dispatched code generation: SSE4_1 SSE4_2 FP16 AVX AVX2
-- requested: SSE4_1 SSE4_2 AVX FP16 AVX2
-- SSE4_1 (3 files): + SSSE3 SSE4_1
-- SSE4_2 (1 files): + SSSE3 SSE4_1 POPCNT SSE4_2
-- FP16 (2 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 AVX
-- AVX (4 files): + SSSE3 SSE4_1 POPCNT SSE4_2 AVX
-- AVX2 (7 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2
--
-- C/C++:
-- Built as dynamic libs?: YES
-- C++11: YES
-- C++ Compiler: /usr/bin/c++ (ver 7.1.1)
-- C++ flags (Release): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -msse -msse2 -msse3 -O2 -DNDEBUG -DNDEBUG
-- C++ flags (Debug): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Wno-narrowing -Wno-delete-non-virtual-dtor -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -msse -msse2 -msse3 -g -O0 -DDEBUG -D_DEBUG
-- C Compiler: /usr/bin/cc
-- C flags (Release): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-narrowing -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -msse -msse2 -msse3 -O2 -DNDEBUG -DNDEBUG
-- C flags (Debug): -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Winit-self -Wno-narrowing -Wno-comment -Wno-implicit-fallthrough -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -msse -msse2 -msse3 -g -O0 -DDEBUG -D_DEBUG
-- Linker flags (Release):
-- Linker flags (Debug):
-- ccache: NO
-- Precompiled headers: YES
-- Extra dependencies: dl m pthread rt
-- 3rdparty dependencies:
--
-- OpenCV modules:
-- To be built: core flann imgproc ml objdetect phase_unwrapping photo plot reg surface_matching video viz xphoto bgsegm face freetype fuzzy img_hash imgcodecs shape videoio xobjdetect highgui superres ts bioinspired dpm features2d line_descriptor saliency text calib3d ccalib cvv datasets rgbd stereo structured_light tracking videostab xfeatures2d ximgproc aruco optflow stitching python2 python3
-- Disabled: js world contrib_world dnn_modern
-- Disabled by dependency: -
-- Unavailable: cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev java cnn_3dobj hdf matlab sfm
--
-- GUI:
-- QT 5.x: YES (ver 5.7.1)
-- QT OpenGL support: NO
-- OpenGL support: NO
-- VTK support: YES (ver 8.1.0)
--
-- Media I/O:
-- ZLib: /lib64/libz.so (ver 1.2.11)
-- JPEG: /lib64/libjpeg.so (ver )
-- WEBP: build (ver encoder: 0x020e)
-- PNG: /lib64/libpng.so (ver 1.6.28)
-- TIFF: /lib64/libtiff.so (ver 42 - 4.0.8)
-- JPEG 2000: build (ver 1.900.1)
-- OpenEXR: build (ver 1.7.1)
-- GDAL: NO
-- GDCM: NO
--
-- Video I/O:
-- DC1394 1.x: NO
-- DC1394 2.x: NO
-- FFMPEG: NO
-- avcodec: NO
-- avformat: NO
-- avutil: NO
-- swscale: NO
-- avresample: NO
-- GStreamer: NO
-- OpenNI: NO
-- OpenNI PrimeSensor Modules: NO
-- OpenNI2: NO
-- PvAPI: NO
-- GigEVisionSDK: NO
-- Aravis SDK: NO
-- UniCap: NO
-- UniCap ucil: NO
-- V4L/V4L2: NO/YES
-- XIMEA: NO
-- Xine: NO
-- Intel Media SDK: NO
-- gPhoto2: NO
--
-- Parallel framework: pthreads
--
-- Trace: YES (with Intel ITT)
--
-- Other third-party libraries:
-- Use Intel IPP: 2017.0.3 [2017.0.3]
-- at: /home/malcolm/external_sources/opencv/build/3rdparty/ippicv/ippicv_lnx
-- Use Intel IPP IW: NO
-- Use VA: NO
-- Use Intel VA-API/OpenCL: NO
-- Use Lapack: NO
-- Use Eigen: YES (ver 3.3.4)
-- Use Cuda: NO
-- Use OpenCL: YES
-- Use OpenVX: NO
-- Use custom HAL: NO
--
-- OpenCL: <Dynamic loading of OpenCL library>
-- Include path: /home/malcolm/external_sources/opencv/3rdparty/include/opencl/1.2
-- Use AMDFFT: NO
-- Use AMDBLAS: NO
--
-- Python 2:
-- Interpreter: /usr/bin/python2.7 (ver 2.7.13)
-- Libraries: /lib64/libpython2.7.so (ver 2.7.13)
-- numpy: /usr/lib64/python2.7/site-packages/numpy/core/include (ver 1.12.1)
-- packages path: lib/python2.7/site-packages
--
-- Python 3:
-- Interpreter: /usr/bin/python3 (ver 3.6.2)
-- Libraries: /lib64/libpython3.6m.so (ver 3.6.2)
-- numpy: /usr/lib64/python3.6/site-packages/numpy/core/include (ver 1.12.1)
-- packages path: lib/python3.6/site-packages
--
-- Python (for build): /usr/bin/python2.7
--
-- Java:
-- ant: NO
-- JNI: NO
-- Java wrappers: NO
-- Java tests: NO
--
-- Matlab: Matlab not found or implicitly disabled
--
-- Documentation:
-- Doxygen: NO
--
-- Tests and samples:
-- Tests: YES
-- Performance tests: YES
-- C/C++ Examples: YES
--
-- Install path: /usr/local
--
-- cvconfig.h is in: /home/malcolm/external_sources/opencv/build
-- -----------------------------------------------------------------
--
-- Configuring done
-- Generating done
-- Build files have been written to: /home/malcolm/external_sources/opencv/build

I used to work until I set BUILD_opencv_dnn and BUILD_opencv_dnn_modernto false. I'm not sure what I'm missing here