contrib module CUDEV uses c++ exceptions but not enabled on Windows

[diablodale]

OpenCV compile that includes contrib module CUDEV, the cmake infrastructure disables C++ exceptions but this module's code needs exceptions. Because of this, the code will behave unpredictably if an exception occurs.

System information (version)

• OpenCV => 4.5.1 at master b19f860
• Operating System / Platform => Microsoft Windows [Version 10.0.19042.867]
• Compiler => VS2019 v16.9.0 64-bit compile

Repro

1. Setup as above.
2. Enable features related to contrib modulke CUDEV
3. Compile debug

Result

This warning is issued during compile:

[build] [1645/2349  69% :: 538.614] Building CXX object modules\cudev\test\CMakeFiles\opencv_test_cudev.dir\test_main.cpp.obj
[build] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\include\ostream(411): warning C4530: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc
[build] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\include\ostream(404): note: while compiling class template member function 'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(double)'
[build] C:\repos-nobackup\opencv\modules\core\include\opencv2/core/utility.hpp(400): note: see reference to function template instantiation 'std::basic_ostream<char,std::char_traits<char>> &std::basic_ostream<char,std::char_traits<char>>::operator <<(double)' being compiled
[build] C:\Program Files (x86)\Microsoft Visual Studio\2019\Community\VC\Tools\MSVC\14.28.29910\include\ostream(641): note: see reference to class template instantiation 'std::basic_ostream<char,std::char_traits<char>>' being compiled

Expected

Clean compile, no warnings, and predictable code execution.

Likely cause

compile_commands.json created by cmake on Windows shows exceptions are not enabled for cudev/test/test_main.cpp

{
  "directory": "C:/repos-nobackup/opencv/build",
  "command": "C:\\PROGRA~2\\MICROS~2\\2019\\COMMUN~1\\VC\\Tools\\MSVC\\1428~1.299\\bin\\Hostx64\\x64\\cl.exe  /nologo /TP -D_USE_MATH_DEFINES -D_VARIADIC_MAX=10 -D__OPENCV_BUILD=1 -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -I. -IC:\\repos-nobackup\\opencv_contrib\\modules\\cudev\\src -IC:\\repos-nobackup\\opencv_contrib\\modules\\cudev\\include -Imodules\\cudev -IC:\\repos-nobackup\\opencv\\modules\\core\\include -Imodules\\cudev\\test -IC:\\repos-nobackup\\opencv\\modules\\imgproc\\include -IC:\\repos-nobackup\\opencv\\modules\\imgcodecs\\include -IC:\\repos-nobackup\\opencv\\modules\\videoio\\include -IC:\\repos-nobackup\\opencv\\modules\\highgui\\include -IC:\\repos-nobackup\\opencv\\modules\\ts\\include -I\"C:\\Program Files\\NVIDIA GPU Computing Toolkit\\CUDA\\v10.1\\include\" -I\"C:\\Program Files (x86)\\Intel\\oneAPI\\ipp\\2021.1.1\\include\"  -DGLOG_NO_ABBREVIATED_SEVERITIES -DWINVER=0x0A00 -D_WIN32_WINNT=0x0A00 -DNTDDI_VERSION=0x0A000005 /arch:AVX  /D _CRT_SECURE_NO_DEPRECATE /D _CRT_NONSTDC_NO_DEPRECATE /D _SCL_SECURE_NO_WARNINGS /Gy /bigobj /Oi  /fp:precise /FS         /arch:AVX  /wd4127 /wd4251 /wd4324 /wd4275 /wd4512 /wd4589 /wd4189 /wd4505  /MD /O2 /Ob2 /DNDEBUG  /GL /Fomodules\\cudev\\test\\CMakeFiles\\opencv_test_cudev.dir\\test_main.cpp.obj /FdTARGET_COMPILE_PDB /FS -c C:\\repos-nobackup\\opencv_contrib\\modules\\cudev\\test\\test_main.cpp",
  "file": "C:\\repos-nobackup\\opencv_contrib\\modules\\cudev\\test\\test_main.cpp"
},

There are only two cpp files in the CUDEV module. The compile command for cudev/src/stub.cpp correctly includes /EHa. A suspicious difference in the two compile commands for each. Notice the two spaces between AVX and /wd4127. This suggests that somewhere is placement for the missing /EHa and cmake chose to not place it yet the surrounding spaces remain.

      below is test_main.cpp
/Gy /bigobj /Oi  /fp:precise /FS         /arch:AVX  /wd4127 /wd4251 /wd4324
/Gy /bigobj /Oi  /fp:precise /FS         /arch:AVX /EHa /wd4127 /wd4251 /wd4324
      above is stub.cpp

I suspect the missing flag is due to the following

opencv/cmake/OpenCVDetectCUDA.cmake

Lines 346 to 358 in b19f860

	macro(ocv_cuda_filter_options)
	foreach(var CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_RELEASE CMAKE_CXX_FLAGS_DEBUG)
	set(${var}_backup_in_cuda_compile_ "${${var}}")
	if (CV_CLANG)
	# we remove -Winconsistent-missing-override and -Qunused-arguments
	# just in case we are compiling CUDA with gcc but OpenCV with clang
	string(REPLACE "-Winconsistent-missing-override" "" ${var} "${${var}}")
	string(REPLACE "-Qunused-arguments" "" ${var} "${${var}}")
	endif()
	# we remove /EHa as it generates warnings under windows
	string(REPLACE "/EHa" "" ${var} "${${var}}")

If the test code needs exceptions (as this warning declares), then the /EHa needs to be used on the compile command. In contrast, if the test code removes its use of exceptions, then exception support is not needed. It is possible to ignore warning 4530, but the test code would still be unpredictable and it might provide invalid test results.

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  forum.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there