Failed to build on Clang/Windows: `W4` and `WX` flags passed to Clang

Open Beginner friendly

#247 opened on Jul 3, 2026 0 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty: 2/5
Estimated time: 1-3 hours
Newbie friendliness: 74/100

Issue type: Bug
Clarity: Mostly clear
Activity status: Quiet
Tech stack: cmake, cpp
Domain: build-system

Research direction

Start in CMake/WarningsAsErrors.cmake and inspect how /W4 and /WX are added to ApprovalTests. Reproduce the Clang-on-Windows configuration with CMake and Ninja, then verify that Clang no longer receives these flags as file paths while the intended warning behavior remains for supported compilers.

Written by the indexing model from the issue text.

Description

Hi, thanks for this amazing library! I've used it a long throughout the years.

I am trying to build approval tests with Clang on Windows, and I got the following error:

clang++: error: no such file or directory: '/W4'
clang++: error: no such file or directory: '/WX'

It appears that those warning flags are being added by CMake/WarningsAsErrors.cmake.

My current escape hatch:

get_target_property(approval_tests_opts ApprovalTests COMPILE_OPTIONS)

if (approval_tests_opts)
    string(REPLACE "/W4" "" approval_tests_opts "${approval_tests_opts}")
    string(REPLACE "/WX" "" approval_tests_opts "${approval_tests_opts}")
    set_target_properties(ApprovalTests PROPERTIES COMPILE_OPTIONS "${approval_tests_opts}")
endif ()

Extra information of my build

Project: Charlie3D
target to build: charlie3d_test

The Approval Test libary are pulled via CPM:

CPMAddPackage(
        NAME approvaltests
        GITHUB_REPOSITORY approvals/ApprovalTests.cpp
        GIT_TAG v.10.13.0
        SYSTEM TRUE
)

CMake generated command:

C:\Users\Lenovo\AppData\Local\Programs\CLion\bin\cmake\win\x64\bin\cmake.exe -DCMAKE_BUILD_TYPE=Debug -DCMAKE_MAKE_PROGRAM=C:/Users/Lenovo/AppData/Local/Programs/CLion/bin/ninja/win/x64/ninja.exe -DBEYOND_CORE_BUILD_TESTS=ON -DCMAKE_TOOLCHAIN_FILE=C:\Users\Lenovo\.clion-vcpkg\vcpkg\scripts\buildsystems\vcpkg.cmake -DCHARLIE3D_BUILD_TESTS=OFF -G Ninja -S E:\Dev\Charlie3D -B E:\Dev\Charlie3D\cmake-build-debug-clang

Other Information:

clang version 21.1.8
Target: x86_64-pc-windows-msvc
cmake version 3.31.6 (CMake; JetBrains IDE bundle; build 29)
OS: Windows 11

Dominant language: C++
Stars: 339
Forks: 55
PR merge metrics: No merged PRs in 30d

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