Compiler option stripped by Visual Studio generator?

Code
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1

It seems the VS 16 code generator is stripping /Wall (all warnings), while the NMake and Ninja generators do not. Is this expected?

cmake version 3.23.1
CMakeLists.txt:

cmake_minimum_required(VERSION 3.16.3)
project(hello)
add_executable(hello hello.c)
target_compile_options(hello PUBLIC /WX /Wall /W4)

cmake -B cmake_out -S . -G "Visual Studio 16 2019" -A Win32
Resulting compiler command:

  C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.29.30133\bin\HostX64\x86\CL.exe /c /Zi /nologo /W4 /WX /diagnostics:column /Od /Ob0 /Oy- /D _MBCS /D WIN32 /D _WINDOWS /D "CMAKE_INTDIR=\"Debug\"" /Gm- /RTC1 /MDd /GS /fp:precise /Zc:wchar_t /Zc:forScope /Zc:inline /Fo"hello.dir\Debug\\" /Fd"hello.dir\Debug\vc142.pdb" /external:W4 /Gd /TC /analyze- /errorReport:queue C:\dev\toolchain\hello.c

Notice that /Wall does not appear on the command line.

cmake -B cmake_out -S . -G "NMake Makefiles"
With NMake, /Wall is present:

        echo  /nologo   /DWIN32 /D_WINDOWS /Zi /Ob0 /Od /RTC1 -MDd /WX /Wall /W4 /showIncludes /FoCMakeFiles\hello.dir\hello.c.obj /FdCMakeFiles\hello.dir\ /FS -c C:\dev\toolchain\hello.c > c:\dev\temp\nm522D.tmp
        C:\dev\cmake-3.23.1-windows-x86_64\cmake-3.23.1-windows-x86_64\bin\cmake.exe -E cmake_cl_compile_depends --dep-file=CMakeFiles\hello.dir\hello.c.obj.d --working-dir=C:\dev\toolchain\cmake_out --filter-prefix="Note: including file: " -- C:\PROGRA~2\MICROS~4\2019\ENTERP~1\VC\Tools\MSVC\1429~1.301\bin\Hostx64\x86\cl.exe @c:\dev\temp\nm522D.tmp

Is this expected?

2

Looks like this is a result of a “lossy” translation to vcxproj and back.

Turns out Wall isn’t being stripped specifically, but earlier options are lost:

Wall: target_compile_options(hello PUBLIC /WX /W4 /Wall)
  W4: target_compile_options(hello PUBLIC /WX /Wall /W4)

The generated vcxproj has the Visual Studio XML setting for warning:

      <WarningLevel>Level4</WarningLevel>

or

      <WarningLevel>EnableAllWarnings</WarningLevel>

based on the last compile option given.

This results in a last-writer-wins overwrite that is different from the behavior of the compiler when both options are provided on the command line (the most verbose option wins).

I had expected target_compile_options to show up as raw compile options on the command line.

3

Sounds like an issue to me, though I’m not sure of the best way to fix it (sounds like a policy would be necessary).

Cc: @brad.king

4

The VS generators parse out flags known to map to specific .vcxproj settings, and generate the settings instead. Both /W4 and /Wall map to the WarningLevel setting. The last one wins, just as /W3 /W4 would choose the latter in a direct cl command-line invocation.