[Bug] IntelliSense ignores "compilerArgs" from c_cpp_properties.json on Windows with MinGW

[M3hul-raj]

Environment

• OS and Version: Windows 11 Version 24H2
• VS Code Version: 1.104.3
• C/C++ Extension Version: 1.27.7
• If using SSH remote, specify OS of remote machine: N/A (local build)

Bug Summary and Steps to Reproduce

Bug Summary: The C/C++ extension's IntelliSense engine does not show any warnings in the "PROBLEMS" tab, even when the compilerArgs in c_cpp_properties.json are set to enable them (-Wall, -Wextra, -Wconversion). The issue occurs on a completely clean installation of VS Code, the C/C++ extension, and the MinGW toolchain.

Steps to reproduce:

1. Perform a full reset of VS Code (by renaming %APPDATA%\Code and %USERPROFILE%.vscode\extensions).
2. Perform a clean install of the MSYS2 toolchain (pacman -S --needed base-devel mingw-w64-ucrt-x86_64-toolchain).
3. Install only the official Microsoft C/C++ extension.
4. Create a project with the following test.cpp file:

#include
#include

int main()
{
// -Wall Test: Unused variable.
int unused_variable;

// -Wextra Test: Comparing signed and unsigned integer.
std::vector<int> my_vector = {1, 2, 3};
int signed_int = -1;
if (signed_int < my_vector.size()) {}

// -Wconversion Test: Implicit conversion that loses data.
long long big_number = 9876543210LL;
int small_number = big_number;
(void)small_number;

}

5. Create the corresponding .vscode/c_cpp_properties.json file.
6. Open the test.cpp file and observe the "PROBLEMS" tab.

Expected behavior: The "PROBLEMS" tab should display three warnings (-Wunused-variable, -Wsign-compare, and -Wconversion) based on the compilerArgs.

Configuration and Logs

c_cpp_properties.json:

{
    "configurations": [
        {
            "name": "Win32",
            "includePath": ["${workspaceFolder}/**"],
            "defines": [],
            "compilerArgs": [
                "-Wall",
                "-Wextra",
                "-Wconversion"
            ],
            "compilerPath": "C:\\msys64\\ucrt64\\bin\\g++.exe",
            "cppStandard": "gnu++23",
            "intelliSenseMode": "windows-gcc-x64"
        }
    ],
    "version": 4
}


Logs from running C/C++: Log Diagnostics:

-------- Diagnostics - 10/8/2025, 12:47:58 AM
Version: 1.27.7
Current Configuration:
{
    "name": "Win32",
    "includePath": [
        "c:/Users/mehul/OneDrive/Desktop/Coding/**"
    ],
    "defines": [
        "_DEBUG",
        "UNICODE",
        "_UNICODE"
    ],
    "compilerArgs": [
        "-Wall",
        "-Wextra",
        "-Wconversion"
    ],
    "compilerPath": "C:\\msys64\\ucrt64\\bin\\g++.exe",
    "cStandard": "gnu23",
    "cppStandard": "gnu++23",
    "intelliSenseMode": "windows-gcc-x64",
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPathInCppPropertiesJson": "C:\\msys64\\ucrt64\\bin\\g++.exe",
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "iostream": "cpp",
        "ostream": "cpp",
        "list": "cpp",
        "random": "cpp",
        "cstdlib": "cpp",
        "cmath": "cpp",
        "numeric": "cpp",
        "iosfwd": "cpp"
    },
    "filesExclude": {
        "**/.git": true,
        "**/.svn": true,
        "**/.hg": true,
        "**/.DS_Store": true,
        "**/Thumbs.db": true
    },
    "filesAutoSaveAfterDelay": false,
    "editorInlayHintsEnabled": true,
    "editorParameterHintsEnabled": true,
    "searchExclude": {
        "**/node_modules": true,
        "**/bower_components": true,
        "**/*.code-search": true
    },
    "workbenchSettingsEditor": "ui"
}
cpptools version (native): 1.27.7.0
Current database path: C:\USERS\MEHUL\APPDATA\LOCAL\MICROSOFT\VSCODE-CPPTOOLS\EAC14729FAC1AD3FDB629C1E532A6DE2\.BROWSE.VC.DB
Translation Unit Mappings:
[ C:\Users\mehul\OneDrive\Desktop\Coding\C++\Recursion\test.cpp - source TU]:
Translation Unit Configurations:
[ C:\Users\mehul\OneDrive\Desktop\Coding\C++\Recursion\test.cpp ]
    Process ID: 5764
    Memory Usage: 198 MB
    Compiler Path: C:\msys64\ucrt64\bin\g++.exe
    Include paths:
        system include: C:\msys64\ucrt64\include\c++\15.2.0
        system include: C:\msys64\ucrt64\include\c++\15.2.0\x86_64-w64-mingw32
        system include: C:\msys64\ucrt64\include\c++\15.2.0\backward
        system include: C:\msys64\ucrt64\lib\gcc\x86_64-w64-mingw32\15.2.0\include
        system include: C:\msys64\ucrt64\include
        system include: C:\msys64\ucrt64\lib\gcc\x86_64-w64-mingw32\15.2.0\include-fixed
    Defines:
        _DEBUG
        UNICODE
        _UNICODE
    Standard Version: c++23
    IntelliSense Mode: windows-gcc-x64
    Other Flags:
        --g++
        --gnu_version=150200
Total Memory Usage: 198 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 4201

Other Extensions

Issue occurs on a fresh VS Code installation with only the ms-vscode.cpptools extension installed. No other extensions are active.

Additional context

Command-line compilation using a batch file with the same compiler and flags works perfectly and shows the warnings when an error is introduced. This confirms the compiler toolchain is functional.

The issue is isolated to the IntelliSense service not respecting the compilerArgs.

The diagnostic log shows that the configuration file is being read correctly, the compiler is found, and the C++ standard is set, but the compilerArgs appear to be ignored by the IntelliSense process.

[Colengms]

Hi @M3hul-raj . I don't think arguments from compilerArgs are being ignored, generally speaking. It looks like the specific arguments you are using do not currently influence IntelliSense.

We have the following existing issue tracking adding the ability to arbitrarily enable/disable specific IntelliSense errors: #2345 I'd suggest up-voting that issue. There is also a workaround suggested there, using #pragmas and error numbers. However, there is not currently a direct association between IntelliSense errors and the set of gcc-specific warnings enabled/disabled using the gcc arguments you provided.

[sean-mcmanus]

This issue tracking potentially showing "warnings" for when a compiler gives warnings and not errors is #828 , but those would be EDG warnings and I'm not sure if all the clang/gcc warnings are supported.

[M3hul-raj]

As a temporary workaround, I have created a manual build task that runs g++ -fsyntax-only. This task correctly populates the 'PROBLEMS' tab with the expected warnings. However, the live IntelliSense engine is still not showing these warnings automatically.