Incorrect C++ standard given while present in compile_commands.json

[BluTree]

Environment

• OS and Version: 26100.3476
• VS Code Version: 1.98.2
• C/C++ Extension Version: 1.24.3 (but bug reproduced in 1.24.2 also)

Bug Summary and Steps to Reproduce

Bug Summary:
The extension fails to set the correct C++ standard, while the file is correctly found in compile_commands.json. In my case, the extension gives the C++17 standard while I'm specifying the C++20 standard.

Steps to reproduce:

1. Write this snippet of code in test.cc:

#include <concepts>

template <typename T>
	requires std::same_as<T, int>
void func(T);

int main(int argc, char** argv)
{
	#ifdef TEST_DEFINE
	func(TEST_DEFINE);
	#endif
	func(1);
	return 0;
}

2. Write a compile_commands.json with this entry:

[
	{
		"directory": "./",
		"command": "clang++ -g -Wall -std=c++20 -DTEST_DEFINE=3",
		"file": "test.cc"
	}
]

3. Setup the compile command in the c_cpp_properties.json
4. Notice the errors on the require keyword, while the TEST_DEFINE define is correctly given

Expected behavior:
The extension should correctly find all the options given to the compiler in compile_commands

On a side note, when I was looking for help in the logs, I noticed this strange error:
Specified compiler was not found: c:\Dev\Sources\C++ tests\clang++ (with c:\Dev\Sources\C++ tests\ being the workspace folder)

This error doesn't appear when running with 1.24.1 version

Configuration and Logs

-------- Diagnostics - 3/22/2025, 11:11:59 PM
Version: 1.24.3
Current Configuration:
{
    "name": "Win32",
    "intelliSenseMode": "windows-clang-x64",
    "compileCommands": [
        "c:\\Dev\\Sources\\C++ tests\\compile_commands.json"
    ],
    "compilerPathIsExplicit": false,
    "cStandardIsExplicit": false,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "compileCommandsInCppPropertiesJson": [
        "compile_commands.json"
    ],
    "cppStandard": "c++17",
    "mergeConfigurations": false,
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.default.compilerPath": "C:\\Dev\\LLVM\\bin\\clang++.exe",
    "C_Cpp.default.cppStandard": "c++17",
    "C_Cpp.exclusionPolicy": "checkFilesAndFolders",
    "C_Cpp.formatting": "clangFormat",
    "C_Cpp.doxygen.generateOnType": false,
    "C_Cpp.codeAnalysis.exclude": {
        "folder": true
    },
    "C_Cpp.codeAnalysis.clangTidy.enabled": true,
    "C_Cpp.codeAnalysis.clangTidy.path": "C:\\Dev\\LLVM\\bin\\clang-tidy.exe",
    "C_Cpp.intelliSenseMemoryLimit": 16384,
    "C_Cpp.loggingLevel": "Debug",
    "C_Cpp.experimentalFeatures": "enabled",
    "C_Cpp.caseSensitiveFileSupport": "enabled"
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": false,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "*.sln": "xml",
        "log": "log",
        "vector": "cpp",
        "concepts": "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): 1.24.3.0
Current database path: C:\Users\Aubin\AppData\Local\Microsoft\vscode-cpptools\2e0838e3c682a3a1661b48151af947ff\.browse.VC.db
Translation Unit Mappings:
[ C:\Dev\Sources\C++ tests\test.cc - source TU]:
Translation Unit Configurations:
[ C:\Dev\Sources\C++ tests\test.cc ]
    Process ID: 18908
    Memory Usage: 61 MB
    Compiler Path: C:\Dev\LLVM\bin\clang.exe
    Include paths:
        system include: C:\Dev\LLVM\lib\clang\19\include
        system include: C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\include
        system include: C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\atlmfc\include
        system include: C:\Windows Kits\10\Include\10.0.22621.0\ucrt
        system include: C:\Windows Kits\10\Include\10.0.22621.0\shared
        system include: C:\Windows Kits\10\Include\10.0.22621.0\um
        system include: C:\Windows Kits\10\Include\10.0.22621.0\winrt
        system include: C:\Windows Kits\10\Include\10.0.22621.0\cppwinrt
    Defines:
        TEST_DEFINE=3
    Standard Version: c++17
    IntelliSense Mode: windows-clang-x64
    Other Flags:
        --clang
        --clang_version=190103
        --ms_compatibility
    compile_commands.json entry:
        directory: c:\Dev\Sources\C++ tests\
        file: C:\Dev\Sources\C++ tests\test.cc
        command: clang++ -g -Wall -std=c++20 -DTEST_DEFINE=3
Total Memory Usage: 61 MB
Browse Paths from compile_commands.json, from workspace folder: C:\Dev\Sources\C++ tests
    C:\Dev\LLVM\lib\clang\19\include
    C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\atlmfc\include
    C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\include
    C:\Dev\Sources\C++ tests
    C:\Windows Kits\10\Include\10.0.22621.0\cppwinrt
    C:\Windows Kits\10\Include\10.0.22621.0\shared
    C:\Windows Kits\10\Include\10.0.22621.0\ucrt
    C:\Windows Kits\10\Include\10.0.22621.0\um
    C:\Windows Kits\10\Include\10.0.22621.0\winrt
    C:\Dev\Sources\C++ tests

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 5387

Other Extensions

No response

Additional context

No response

[sean-mcmanus]

@BluTree How you are expecting the "clang++.exe" in your compile_commands.json to be resolved into a full path? My guess is that we're throwing out the arguments in your compile_commands.json because we don't resolve the "clang++" to a full path and then we fall back to using your C_Cpp.default.compilerPath but without the arguments. Can you set C_Cpp.default.compilerArgs to "-std=c++20 -DTEST_DEFINE=3" or something like that?

Or somehow make a change to ensure clang++.exe can resolve to a full path? Or do you think we should be doing that automatically somehow?

[BluTree]

How you are expecting the "clang++.exe" in your compile_commands.json to be resolved into a full path?

I was assuming the PATH would be used to resolve this. And I can confirm this behavior worked on 1.24.1. I tried replacing clang++ to clang-cl, just to verify, and the logs clearly indicate it resolves correctly to the compiler path, while it fails in 1.24.2 and later.

1.24.1:
Querying compiler for default C++ language standard using command line: C:\Dev\LLVM\bin\clang-cl.exe /TP /clang:-E /clang:-dM nul

Diagnostic Logs

-------- Diagnostics - 3/24/2025, 5:56:33 PM
Version: 1.24.1
Current Configuration:
{
    "name": "Win32",
    "intelliSenseMode": "windows-clang-x64",
    "compileCommands": [
        "c:\\Dev\\Sources\\C++ tests/compile_commands.json"
    ],
    "compilerPathIsExplicit": false,
    "cStandardIsExplicit": false,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "compileCommandsInCppPropertiesJson": [
        "${workspaceFolder}/compile_commands.json"
    ],
    "cppStandard": "c++17",
    "mergeConfigurations": false,
    "browse": {
        "path": [
            "${workspaceFolder}"
        ],
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.default.compilerPath": "C:\\Dev\\LLVM\\bin\\clang++.exe",
    "C_Cpp.default.cppStandard": "c++17",
    "C_Cpp.exclusionPolicy": "checkFilesAndFolders",
    "C_Cpp.formatting": "clangFormat",
    "C_Cpp.doxygen.generateOnType": false,
    "C_Cpp.codeAnalysis.exclude": {
        "folder": true
    },
    "C_Cpp.codeAnalysis.clangTidy.enabled": true,
    "C_Cpp.codeAnalysis.clangTidy.path": "C:\\Dev\\LLVM\\bin\\clang-tidy.exe",
    "C_Cpp.intelliSenseMemoryLimit": 16384,
    "C_Cpp.loggingLevel": "Debug",
    "C_Cpp.experimentalFeatures": "enabled",
    "C_Cpp.caseSensitiveFileSupport": "enabled"
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": false,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "*.sln": "xml",
        "log": "log",
        "vector": "cpp",
        "concepts": "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): 1.24.1.0
Current database path: C:\Users\Aubin\AppData\Local\Microsoft\vscode-cpptools\2e0838e3c682a3a1661b48151af947ff\.browse.VC.db
Translation Unit Mappings:
[ C:\Dev\Sources\C++ tests\test.cc - source TU]:
Translation Unit Configurations:
[ C:\Dev\Sources\C++ tests\test.cc ]
    Process ID: 33464
    Memory Usage: 73 MB
    Compiler Path: C:\Dev\LLVM\bin\clang-cl.exe
    Includes:
    System Includes:
        C:\Dev\LLVM\lib\clang\20\include
        C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\include
        C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\atlmfc\include
        C:\Windows Kits\10\Include\10.0.22621.0\ucrt
        C:\Windows Kits\10\Include\10.0.22621.0\shared
        C:\Windows Kits\10\Include\10.0.22621.0\um
        C:\Windows Kits\10\Include\10.0.22621.0\winrt
        C:\Windows Kits\10\Include\10.0.22621.0\cppwinrt
    Defines:
        TEST_DEFINE=3
    Standard Version: c++20
    IntelliSense Mode: windows-clang-x64
    Other Flags:
        --clang
        --clang_version=200100
        --ms_compatibility
    compile_commands.json entry:
        directory: C:\Dev\Sources\C++ tests
        file: C:\Dev\Sources\C++ tests\test.cc
        command: clang-cl -std:c++20 -DTEST_DEFINE=3
Total Memory Usage: 73 MB
Browse Paths from compile_commands.json, from workspace folder: C:\Dev\Sources\C++ tests
    C:\Dev\Sources\C++ tests

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 9263

1.24.3:
Specified compiler was not found: C:\Dev\Sources\C++ tests\clang-cl

Diagnostic Logs

-------- Diagnostics - 3/24/2025, 5:59:07 PM
Version: 1.24.3
Current Configuration:
{
    "name": "Win32",
    "intelliSenseMode": "windows-clang-x64",
    "compileCommands": [
        "c:\\Dev\\Sources\\C++ tests/compile_commands.json"
    ],
    "compilerPathIsExplicit": false,
    "cStandardIsExplicit": false,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "compileCommandsInCppPropertiesJson": [
        "${workspaceFolder}/compile_commands.json"
    ],
    "cppStandard": "c++17",
    "mergeConfigurations": false,
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.default.compilerPath": "C:\\Dev\\LLVM\\bin\\clang++.exe",
    "C_Cpp.default.cppStandard": "c++17",
    "C_Cpp.exclusionPolicy": "checkFilesAndFolders",
    "C_Cpp.formatting": "clangFormat",
    "C_Cpp.doxygen.generateOnType": false,
    "C_Cpp.codeAnalysis.exclude": {
        "folder": true
    },
    "C_Cpp.codeAnalysis.clangTidy.enabled": true,
    "C_Cpp.codeAnalysis.clangTidy.path": "C:\\Dev\\LLVM\\bin\\clang-tidy.exe",
    "C_Cpp.intelliSenseMemoryLimit": 16384,
    "C_Cpp.loggingLevel": "Debug",
    "C_Cpp.experimentalFeatures": "enabled",
    "C_Cpp.caseSensitiveFileSupport": "enabled"
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": false,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "*.sln": "xml",
        "log": "log",
        "vector": "cpp",
        "concepts": "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): 1.24.3.0
Current database path: C:\Users\Aubin\AppData\Local\Microsoft\vscode-cpptools\2e0838e3c682a3a1661b48151af947ff\.browse.VC.db
Translation Unit Mappings:
[ C:\Dev\Sources\C++ tests\test.cc - source TU]:
Translation Unit Configurations:
[ C:\Dev\Sources\C++ tests\test.cc ]
    Process ID: 3376
    Memory Usage: 62 MB
    Compiler Path: C:\Dev\LLVM\bin\clang.exe
    Include paths:
        system include: C:\Dev\LLVM\lib\clang\20\include
        system include: C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\include
        system include: C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\atlmfc\include
        system include: C:\Windows Kits\10\Include\10.0.22621.0\ucrt
        system include: C:\Windows Kits\10\Include\10.0.22621.0\shared
        system include: C:\Windows Kits\10\Include\10.0.22621.0\um
        system include: C:\Windows Kits\10\Include\10.0.22621.0\winrt
        system include: C:\Windows Kits\10\Include\10.0.22621.0\cppwinrt
    Defines:
        TEST_DEFINE=3
    Standard Version: c++17
    IntelliSense Mode: windows-clang-x64
    Other Flags:
        --clang
        --clang_version=200100
        --ms_compatibility
    compile_commands.json entry:
        directory: C:\Dev\Sources\C++ tests
        file: C:\Dev\Sources\C++ tests\test.cc
        command: clang-cl -std:c++20 -DTEST_DEFINE=3
Total Memory Usage: 62 MB
Browse Paths from compile_commands.json, from workspace folder: C:\Dev\Sources\C++ tests
    C:\Dev\LLVM\lib\clang\20\include
    C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\atlmfc\include
    C:\Dev\Microsoft Visual Studio\2022\Community\VC\Tools\MSVC\14.41.34120\include
    C:\Dev\Sources\C++ tests
    C:\Windows Kits\10\Include\10.0.22621.0\cppwinrt
    C:\Windows Kits\10\Include\10.0.22621.0\shared
    C:\Windows Kits\10\Include\10.0.22621.0\ucrt
    C:\Windows Kits\10\Include\10.0.22621.0\um
    C:\Windows Kits\10\Include\10.0.22621.0\winrt

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 5423

Can you set C_Cpp.default.compilerArgs to "-std=c++20 -DTEST_DEFINE=3" or something like that?

I tried specifying the C_Cpp.default.compilerArgs, and it worked as intended.