System information (version)

• OpenCV => 3.4.2
• Operating System / Platform = macOS 10.13.6
• Compiler = Xcode Version 10.0 beta 6 (10L232m)

Detailed description

OpenCV iOS framework build fails against most recent Xcode 10 beta. The following error occurs:

CMake Error at cmake/OpenCVCompilerOptimizations.cmake:458 (message):
  Required baseline optimization is not supported: NEON
  (CPU_BASELINE_REQUIRE=;NEON)
Call Stack (most recent call first):
  cmake/OpenCVCompilerOptions.cmake:259 (include)
  CMakeLists.txt:555 (include)


-- Performing Test HAVE_CPU_BASELINE_FLAGS
-- Performing Test HAVE_CPU_BASELINE_FLAGS - Failed
CMake Error at cmake/OpenCVCompilerOptimizations.cmake:505 (message):
  Compiler doesn't support baseline optimization flags:
Call Stack (most recent call first):
  cmake/OpenCVCompilerOptions.cmake:261 (ocv_compiler_optimization_options)
  CMakeLists.txt:555 (include)

I realize that this is a beta version of Xcode, but the final version is expected to be released next week, and I was hoping someone else may have seen this issue. Full log is here: https://gist.github.com/amrox/522e7968c5badbb2fdd168068843e808

This seems very similar to
#10363 #8945 but this issue is said to be fixed in 3.4.1, and I'm still seeing it in 3.4.2 and 3.4.3.

Finally this only happens when using the Xcode beta toolchain. If I switch back to Xcode 9.4.1 (9F2000) it builds fine.

Steps to reproduce

1. Checkout opencv, tested against 3.4.3 3.4.2 and d74b98c3d9264f9623b27a8d4e0fc92ac97b71d0
2. build iOS framework with: python platforms/ios/build_framework.py build/ios

Edit:

It appears the real problem is due to the fact that libstdc++ is deprecated in Xcode 10 / iOS 12 toolchain and Apple wants you to move to libc++

CMakeError.log: CMakeError.log