CMakeLists.txt: Needs CMAKE_CXX_STANDARD=11

[jenisys]

Description

CMake build currently fails to compile on macOS (with AppleClang 10.0.0).
Doctest 2.2.2 / 2.3 or newer requires C++11 or newer, at least in the default configuration.
The default C++ compiler standard depends largely on the current toolchain / compiler version. Therefore, it would be much more robust to describe this requirement.

WORKAROUND: Fixes the problem

# -- FILE: doctest/CMakeLists.txt
...
project(doctest VERSION ${ver})
# CHANGE-NEEDED: Use C++11 standard as default for all C++ targets.
set(CMAKE_CXX_STANDARD 11)  
...

ALTERNATIVE:
Set target properties to CXX_STANDARD=11 on all examples/.../CMakeLists.txt files where this information is currently missing

Steps to reproduce

1. Checkout / clone doctest git repository
2. Run cmake build (with platform / toolchain environment described above)

cmake --build .
[2/44] Building CXX object examples/all_features/CMakeFiles/disabled.dir/alternative_macros.cpp.o
FAILED: examples/all_features/CMakeFiles/disabled.dir/alternative_macros.cpp.o 
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++  -DDOCTEST_CONFIG_DISABLE -I../scripts/development_only -I../doctest/parts -Werror -pedantic -pedantic-errors -fvisibility=hidden -fstrict-aliasing -Weverything -Wno-c++98-compat -Wno-c++98-compat-pedantic -Wno-c++98-compat-bind-to-temporary-copy -Wno-c++98-compat-local-type-template-args -Qunused-arguments -fcolor-diagnostics -g -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk   -Wno-unknown-warning-option -Wno-unneeded-internal-declaration -Wno-unused-function -Wno-unused-parameter -Wno-unused-variable -Wno-unused-template -MD -MT examples/all_features/CMakeFiles/disabled.dir/alternative_macros.cpp.o -MF examples/all_features/CMakeFiles/disabled.dir/alternative_macros.cpp.o.d -o examples/all_features/CMakeFiles/disabled.dir/alternative_macros.cpp.o -c ../examples/all_features/alternative_macros.cpp
In file included from ../examples/all_features/alternative_macros.cpp:1:
In file included from ../examples/all_features/doctest_proxy.h:6:
In file included from ../scripts/development_only/doctest/doctest.h:1:
../doctest/parts/doctest_fwd.h:400:1: error: inline namespaces are a C++11 feature [-Werror,-Wc++11-inline-namespace]
DOCTEST_STD_NAMESPACE_BEGIN
^
... (more C++11 compile errors)

Extra information

• doctest version: v2.2.2 or newer (also current HEAD)
• Operating System: macOS 10.14
• Compiler+version: AppleClang 10.0.0

[onqtam]

Thanks for reporting! Seems that this is not enough - we forgot the case when someone is building the doctest repository itself (and not using it as a sub project)