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
@@ -35,7 +35,6 @@ install:
     if ($env:APPVEYOR_JOB_NAME -like "*Visual Studio 2017*") {
       $env:CMAKE_GENERATOR = "Visual Studio 15 2017"
       $env:CMAKE_INCLUDE_PATH = "C:\Libraries\boost_1_64_0"
-      $env:CXXFLAGS = "-permissive-"
     } else {
       $env:CMAKE_GENERATOR = "Visual Studio 14 2015"
     }
@@ -57,14 +56,15 @@ 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 --version
 - cmake -G "%CMAKE_GENERATOR%" -A "%CMAKE_ARCH%"
-    -DPYBIND11_CPP_STANDARD="/std:c++%CPP%"
+    -DPYBIND11_CPP_STANDARD="/std:c++17"
     -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

@@ -20,7 +20,7 @@ include(CMakeParseArguments)
 
 # Use the language standards abstraction if CMake supports it with the current compiler
 if(NOT CMAKE_VERSION VERSION_LESS 3.1)
-  if(NOT CMAKE_CXX_STANDARD)
+  if(NOT CMAKE_CXX_STANDARD AND NOT PYBIND11_CPP_STANDARD)
     if(CMAKE_CXX14_STANDARD_COMPILE_OPTION)
       set(CMAKE_CXX_STANDARD 14)
     elseif(CMAKE_CXX11_STANDARD_COMPILE_OPTION)
@@ -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 = ${PYBIND11_CPP_STANDARD})
+
 # Checks whether the given CXX/linker flags can compile and link a cxx file.  cxxflags and
 # linkerflags are lists of flags to use.  The result variable is a unique variable name for each set
 # of flags: the compilation result will be cached base on the result variable.  If the flags work,
@@ -218,8 +220,10 @@ function(pybind11_add_module target_name)
   # Make sure C++11/14 are enabled
   if(PYBIND11_CPP_STANDARD)
     if(CMAKE_VERSION VERSION_LESS 3.3 OR CMAKE_GENERATOR MATCHES "Visual Studio")
+      message("HERE, I hope?")
       target_compile_options(${target_name} PUBLIC ${PYBIND11_CPP_STANDARD})
     else()
+      message("NOT HERE, I hope?")
       target_compile_options(${target_name} PUBLIC $<$<COMPILE_LANGUAGE:CXX>:${PYBIND11_CPP_STANDARD}>)
     endif()
   endif()