Honest advertising on supported language versions

[MathiasMagnus]

Expected Behavior

If C++17* support (*with limitations) is advertised, things should mostly work when in C++17 mode.

Actual Behavior

Even

int main() {
  boost::ut::expect(true);
}

fails to compile with MSVC saying:

[build] C:\Users\mnagy\Source\Repos\ut\.vscode\install\include\boost/ut.hpp(1402): error C7555: use of designated initializers requires at least '/std:c++latest'
[build] C:\Users\mnagy\Source\Repos\ut\.vscode\install\include\boost/ut.hpp(1402): note: This diagnostic occurred in the compiler generated function 'auto boost::ext::ut::v1_1_8::runner<TReporter,MaxPathSize>::on(boost::ext::ut::v1_1_8::events::test<Ts...>)'

This issue is not unique to MSVC, even Appveyor build with clang-cl have output such as:

[57/112] Building CXX object example\CMakeFiles\boost_ut_parameterized.dir\parameterized.cpp.obj
..\example\parameterized.cpp(30,20): warning: explicit template parameter list for lambdas is a C++20 extension [-Wc++20-extensions]
  "types"_test = []<class T>() {
                   ^

When the entry points to testing use C++20 features, I naturally don't expect Boost UT to work in C++17 mode, but most features should have C++17 workarounds (hence the asterisk "with limitations").

Either decide whether the library supports C++17 or not. If yes, actually specify/mark which features are known to not work. Run strict C++17 builds in CI (-Werror) and disable such tests on purpose if there are no workarounds implemented.

BTW, this regression was introduced in v1.1.5, as installing tagged version of v1.1.4 compiles the simplest example as intended.

Steps to Reproduce the Problem

cmake_minimum_required(VERSION 3.0)

project(Test-Boost.UT
  LANGUAGES CXX
)

if (MSVC)
  string(REGEX REPLACE "/W[0-9]" "" CMAKE_CXX_FLAGS ${CMAKE_CXX_FLAGS})
endif (MSVC)

find_package(ut REQUIRED)

add_executable(Test1 Test1.cpp)

target_link_libraries(Test1
  PRIVATE
    boost::ut
)

target_compile_options(Test1
  PRIVATE
    $<$<CXX_COMPILER_ID:MSVC>:
      /W4          # Turn on all (sensible) warnings
      /permissive- # Turn on strict language conformance
      /EHsc        # Specify exception handling model
    >
)

2. C:\Kellekek\Microsoft\VisualStudio\2019\BuildTools\VC\Tools\MSVC\14.26.28801\bin\Hostx64\x64\cl.exe /nologo /TP -IC:\Users\mnagy\Source\Repos\ut\.vscode\install\include /DWIN32 /D_WINDOWS /GR /EHsc /MDd /Zi /Ob0 /Od /RTC1 /W4 /permissive- /EHsc /std:c++17 /showIncludes /FoCMakeFiles\Test1.dir\Test1.cpp.obj /FdCMakeFiles\Test1.dir\ /FS -c ..\..\Test1.cpp

Specifications

• Version: 1.1.5+
• Platform: Windows
• Subsystem: ?