[Bug] "Compile Active File" misquotes /Fd<dir>\ trailing backslash, consuming the next compiler flag

[namelessmasses]

Brief Issue Summary

When using "Compile Active File" with MSVC + Ninja Multi-Config on Windows, CMake Tools incorrectly quotes compiler arguments that end with a backslash. CMake emits /Fd

\ (with a trailing backslash) when no explicit PDB name is configured. CMake Tools wraps this in quotes, but in cmd.exe a backslash before a closing quote is an escape — so the quote is not treated as closing and the next token (/FS) is consumed as part of the argument.

Observed compile command:

"/FdCMakeFiles\INPUT_TESTS.dir\RelWithDebInfo\ /FS"
cl.exe error:

fatal error C1041: cannot open program database
'...\CMakeFiles\INPUT_TESTS.dir\RelWithDebInfo\ \FS.pdb';
if multiple CL.EXE write to the same .PDB file, please use /FS
cl.exe receives /Fd

\ /FS as a single argument and interprets \FS.pdb as the PDB filename. The /FS flag is lost.

Expected: Arguments with trailing backslashes are quoted correctly, e.g. by doubling the backslash or appending a space before the closing quote ("/FdCMakeFiles\INPUT_TESTS.dir\RelWithDebInfo\ ") — or by not quoting the argument at all since it contains no spaces.

Workaround: Set COMPILE_PDB_NAME on the target so CMake emits an explicit filename (/Fd

<name>.pdb) instead of a bare directory path, eliminating the trailing backslash.

Steps to reproduce:

CMake project, Ninja Multi-Config generator, MSVC toolchain, CMAKE_EXPORT_COMPILE_COMMANDS=ON
Do not set COMPILE_PDB_NAME on any target (default CMake behaviour)
Open a .cpp source file and run CMake: Compile Active File
Environment:

Windows 11
MSVC (cl.exe)
Generator: Ninja Multi-Config
CMake Tools version: 1.23.52
VS Code version: 1.117.0

CMake Tools Diagnostics

{
  "os": "win32",
  "vscodeVersion": "1.117.0",
  "cmtVersion": "1.23.52",
  "configurations": [
    {
      "folder": "d:\\src\\thx\\SonicSnitch\\DetectionEngine\\InversePanning",
      "cmakeVersion": "4.2.3",
      "configured": true,
      "generator": "Ninja Multi-Config",
      "usesPresets": true,
      "compilers": {
        "CXX": "C:/Program Files/Microsoft Visual Studio/18/Community/VC/Tools/MSVC/14.50.35717/bin/Hostx64/x64/cl.exe"
      }
    }
  ],
  "cpptoolsIntegration": {
    "isReady": true,
    "hasCodeModel": true,
    "activeBuildType": "Debug",
    "buildTypesSeen": [
      "Debug",
      "Release",
      "RelWithDebInfo"
    ],
    "requests": [
      "file:///d%3A/src/thx/SonicSnitch/DetectionEngine/InversePanning/tests/decoder_pump_test.cpp",
      "file:///d%3A/src/thx/SonicSnitch/DetectionEngine/InversePanning/DemoUI/src/InputSources/FFmpeg/FFmpegInputSource.cpp"
    ],
    "responses": [
      {
        "uri": "file:///d%3A/src/thx/SonicSnitch/DetectionEngine/InversePanning/tests/decoder_pump_test.cpp",
        "configuration": {
          "includePath": [
            "d:/src/thx/sonicsnitch/detectionengine/inversepanning/src",
            "d:/src/thx/sonicsnitch/detectionengine/inversepanning/demoui/src",
            "d:/src/thx/sonicsnitch/detectionengine/inversepanning/build/ninja/with-vcpkg-qt-online/vcpkg_installed/x64-windows/include",
            "c:/qt/6.11.0/msvc2022_64/include/qtcore",
            "c:/qt/6.11.0/msvc2022_64/include",
            "c:/qt/6.11.0/msvc2022_64/mkspecs/win32-msvc"
          ],
          "defines": [
            "GTEST_LINKED_AS_SHARED_LIBRARY=1",
            "QT_CORE_LIB",
            "TEST_CONTENT_DIR=\"D:/src/thx/SonicSnitch/DetectionEngine/InversePanning/../test-content\"",
            "UNICODE",
            "WIN32",
            "WIN64",
            "_ENABLE_EXTENDED_ALIGNED_STORAGE",
            "_UNICODE",
            "_WIN64"
          ],
          "compilerPath": "c:/program files/microsoft visual studio/18/community/vc/tools/msvc/14.50.35717/bin/hostx64/x64/cl.exe",
          "compilerArgs": [],
          "compilerFragments": [
            "/DWIN32 /D_WINDOWS /EHsc /Zi /Ob0 /Od /RTC1 -std:c++latest -MDd",
            "-Zc:__cplusplus",
            "-permissive-",
            "-utf-8"
          ]
        }
      },
      {
        "uri": "file:///d%3A/src/thx/SonicSnitch/DetectionEngine/InversePanning/DemoUI/src/InputSources/FFmpeg/FFmpegInputSource.cpp",
        "configuration": {
          "includePath": [
            "d:/src/thx/sonicsnitch/detectionengine/inversepanning/src",
            "d:/src/thx/sonicsnitch/detectionengine/inversepanning/demoui/src",
            "d:/src/thx/sonicsnitch/detectionengine/inversepanning/build/ninja/with-vcpkg-qt-online/vcpkg_installed/x64-windows/include",
            "c:/qt/6.11.0/msvc2022_64/include/qtcore",
            "c:/qt/6.11.0/msvc2022_64/include",
            "c:/qt/6.11.0/msvc2022_64/mkspecs/win32-msvc"
          ],
          "defines": [
            "GTEST_LINKED_AS_SHARED_LIBRARY=1",
            "QT_CORE_LIB",
            "TEST_CONTENT_DIR=\"D:/src/thx/SonicSnitch/DetectionEngine/InversePanning/../test-content\"",
            "UNICODE",
            "WIN32",
            "WIN64",
            "_ENABLE_EXTENDED_ALIGNED_STORAGE",
            "_UNICODE",
            "_WIN64"
          ],
          "compilerPath": "c:/program files/microsoft visual studio/18/community/vc/tools/msvc/14.50.35717/bin/hostx64/x64/cl.exe",
          "compilerArgs": [],
          "compilerFragments": [
            "/DWIN32 /D_WINDOWS /EHsc /Zi /Ob0 /Od /RTC1 -std:c++latest -MDd",
            "-Zc:__cplusplus",
            "-permissive-",
            "-utf-8"
          ]
        }
      }
    ],
    "partialMatches": [],
    "targetCount": 42,
    "executablesCount": 11,
    "librariesCount": 1,
    "targets": []
  },
  "settings": [
    {
      "communicationMode": "automatic",
      "useCMakePresets": "always",
      "configureOnOpen": false
    }
  ]
}

Debug Log

[configure-debug.log](https://github.com/user-attachments/files/26993568/configure-debug.log)

Additional Information

This repo is a minimal configuartion to reproduce.

[yanghhhhhhh]

Hi @namelessmasses , thanks for reporting issue here!
We can reproduce this issue on Visual Studio Code v1.117.0 + CMake Tools v1.23.52 release version.

Repro Steps:

1. Clone the project and open it.
2. Open .cpp file, run command "CMake: Compile Active file" and observe the result.

Details please see following video:

FYI: @gcampbell-msft