Debugging non-failure of /std:c++17

Author: YannickJadoul

.appveyor.yml

@@ -12,10 +12,10 @@ platform:
 environment:
   matrix:
   - PYTHON: 36
-    CPP: 14
+    CPP: 17
     CONFIG: Debug
   - PYTHON: 27
-    CPP: 14
+    CPP: 17
     CONFIG: Debug
   - CONDA: 36
     CPP: 17
@@ -57,14 +57,15 @@ install:
     7z x 3.3.3.zip -y > $null
     $env:CMAKE_INCLUDE_PATH = "eigen-eigen-67e894c6cd8f;$env:CMAKE_INCLUDE_PATH"
 build_script:
+- set VERBOSE=1
 - cmake -G "%CMAKE_GENERATOR%" -A "%CMAKE_ARCH%"
     -DPYBIND11_CPP_STANDARD="/std:c++%CPP%"
     -DPYBIND11_WERROR=ON
     -DDOWNLOAD_CATCH=ON
     -DCMAKE_SUPPRESS_REGENERATION=1
     .
 - set MSBuildLogger="C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll"
-- cmake --build . --config %CONFIG% --target pytest -- /m /v:m /logger:%MSBuildLogger%
-- cmake --build . --config %CONFIG% --target cpptest -- /m /v:m /logger:%MSBuildLogger%
-- if "%CPP%"=="17" (cmake --build . --config %CONFIG% --target test_cmake_build -- /m /v:m /logger:%MSBuildLogger%)
+- cmake --build . --config %CONFIG% --target pytest -- /m /logger:%MSBuildLogger%
+- cmake --build . --config %CONFIG% --target cpptest -- /m /logger:%MSBuildLogger%
+- if "%CPP%"=="17" (cmake --build . --config %CONFIG% --target test_cmake_build -- /m /logger:%MSBuildLogger%)
 on_failure: if exist "tests\test_cmake_build" type tests\test_cmake_build\*.log*

tools/pybind11Tools.cmake

@@ -56,6 +56,8 @@ if(NOT PYBIND11_CPP_STANDARD AND NOT CMAKE_CXX_STANDARD)
       "C++ standard flag, e.g. -std=c++11, -std=c++14, /std:c++14.  Defaults to C++14 mode." FORCE)
 endif()
 
+message(PYBIND11_CPP_STANDARD = ${PYBIND11_CPP_STANDARD})
+
 # Checks whether the given CXX/linker flags can compile and link a cxx file.  cxxflags and
 # linkerflags are lists of flags to use.  The result variable is a unique variable name for each set
 # of flags: the compilation result will be cached base on the result variable.  If the flags work,