microsoft / microsoft/vscode-cpptools

Add support for clang-cl behavior for `/external:I`

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#14,186 3 comments 0 reactions 1 assignee View on GitHub

@Colengms is already working on this.

Since Feb 12, 2026.

bug compiler support fixed Language Service
Dominant language
TypeScript
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Description

Environment

  • OS and Version: Windows 10
  • VS Code Version: 1.109.2
  • C/C++ Extension Version: 1.30.5

Bug Summary

/external:I in compilerArgs for MSVC are not treated as system include directories as shown in C/C++ Diagnostic:

    Include paths:
        include: C:\tmp\.vscode

But for clang++ -isystem, it is correctly detected as system include:

    Include paths:
        system include (isystem): C:\tmp\.vscode

clang-cl -imsvc as well:

    Include paths:
        system include: C:\Program Files\LLVM\lib\clang\21\include
        system include: C:\tmp\.vscode

Configuration and Logs

C/C++ Diagnostic for MSVC /external:I 
-------- Diagnostics - 2026/2/13 00:47:56
Version: 1.30.5
Current Configuration:
{
    "name": "Test",
    "intelliSenseMode": "windows-msvc-x64",
    "compilerArgs": [
        "/external:I${workspaceFolder}/.vscode"
    ],
    "compilerPathIsExplicit": false,
    "cStandardIsExplicit": false,
    "cppStandardIsExplicit": false,
    "intelliSenseModeIsExplicit": true,
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "windowsSdkVersion": "10.0.26100.0",
    "cStandard": "c17",
    "cppStandard": "c++17",
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "compilerPath": "C:\\Program Files\\Microsoft Visual Studio\\18\\Enterprise\\VC\\Tools\\MSVC\\14.50.35717\\bin\\Hostx64\\x64\\cl.exe",
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {},
    "filesExclude": {
        "**/.git": true,
        "**/.svn": true,
        "**/.hg": true,
        "**/.DS_Store": true,
        "**/Thumbs.db": true,
        "**/.classpath": true,
        "**/.project": true,
        "**/.settings": true,
        "**/.factorypath": true
    },
    "filesAutoSaveAfterDelay": false,
    "editorInlayHintsEnabled": true,
    "editorParameterHintsEnabled": true,
    "searchExclude": {
        "**/node_modules": true,
        "**/bower_components": true,
        "**/*.code-search": true
    },
    "workbenchSettingsEditor": "ui"
}
cpptools version (native): 1.30.5.0
Current database path: C:\USERS\HUANGQINJIN\APPDATA\LOCAL\MICROSOFT\VSCODE-CPPTOOLS\90D20250051651E1D809C1C7E0C52070\.BROWSE.VC.DB
Translation Unit Mappings:
[ C:\tmp\main.cpp - source TU]:
Translation Unit Configurations:
[ C:\tmp\main.cpp ]
    Process ID: 2948
    Memory Usage: 50 MB
    Compiler Path: C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Tools\MSVC\14.50.35717\bin\Hostx64\x64\cl.exe
    Include paths:
        include: C:\tmp\.vscode
        system include: C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Tools\MSVC\14.50.35717\include
        system include: C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Tools\MSVC\14.50.35717\atlmfc\include
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\um
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\ucrt
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\shared
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\winrt
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\cppwinrt
    Standard Version: ms_c++17
    IntelliSense Mode: windows-msvc-x64
Total Memory Usage: 50 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 5348
C/C++ Diagnostic for clang++ -isystem 
-------- Diagnostics - 2026/2/13 00:52:26
Version: 1.30.5
Current Configuration:
{
    "name": "Test",
    "compilerPath": "C:\\Program Files\\LLVM\\bin\\clang++.exe",
    "compilerArgs": [
        "-isystem${workspaceFolder}/.vscode"
    ],
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": false,
    "cppStandardIsExplicit": false,
    "intelliSenseModeIsExplicit": false,
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPathInCppPropertiesJson": "C:\\Program Files\\LLVM\\bin\\clang++.exe",
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {},
    "filesExclude": {
        "**/.git": true,
        "**/.svn": true,
        "**/.hg": true,
        "**/.DS_Store": true,
        "**/Thumbs.db": true,
        "**/.classpath": true,
        "**/.project": true,
        "**/.settings": true,
        "**/.factorypath": true
    },
    "filesAutoSaveAfterDelay": false,
    "editorInlayHintsEnabled": true,
    "editorParameterHintsEnabled": true,
    "searchExclude": {
        "**/node_modules": true,
        "**/bower_components": true,
        "**/*.code-search": true
    },
    "workbenchSettingsEditor": "ui"
}
cpptools version (native): 1.30.5.0
Current database path: C:\USERS\HUANGQINJIN\APPDATA\LOCAL\MICROSOFT\VSCODE-CPPTOOLS\90D20250051651E1D809C1C7E0C52070\.BROWSE.VC.DB
Translation Unit Mappings:
[ C:\tmp\main.cpp - source TU]:
Translation Unit Configurations:
[ C:\tmp\main.cpp ]
    Process ID: 15408
    Memory Usage: 51 MB
    Compiler Path: C:\Program Files\LLVM\bin\clang++.exe
    Include paths:
        system include (isystem): C:\tmp\.vscode
        system include: C:\Program Files\LLVM\lib\clang\21\include
        system include: C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Tools\MSVC\14.50.35717\include
        system include: C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Tools\MSVC\14.50.35717\atlmfc\include
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\ucrt
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\shared
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\um
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\winrt
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\cppwinrt
    Standard Version: c++14
    IntelliSense Mode: windows-clang-x64
    Other Flags:
        --clang
        --clang_version=210108
        --ms_compatibility
Total Memory Usage: 51 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 6459
Number of files parsed: 1
C/C++ Diagnostic for clang-cl -imsvc 
-------- Diagnostics - 2026/2/13 00:53:17
Version: 1.30.5
Current Configuration:
{
    "name": "Test",
    "compilerPath": "C:\\Program Files\\LLVM\\bin\\clang-cl.exe",
    "compilerArgs": [
        "-imsvc${workspaceFolder}/.vscode"
    ],
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": false,
    "cppStandardIsExplicit": false,
    "intelliSenseModeIsExplicit": false,
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPathInCppPropertiesJson": "C:\\Program Files\\LLVM\\bin\\clang-cl.exe",
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {},
    "filesExclude": {
        "**/.git": true,
        "**/.svn": true,
        "**/.hg": true,
        "**/.DS_Store": true,
        "**/Thumbs.db": true,
        "**/.classpath": true,
        "**/.project": true,
        "**/.settings": true,
        "**/.factorypath": true
    },
    "filesAutoSaveAfterDelay": false,
    "editorInlayHintsEnabled": true,
    "editorParameterHintsEnabled": true,
    "searchExclude": {
        "**/node_modules": true,
        "**/bower_components": true,
        "**/*.code-search": true
    },
    "workbenchSettingsEditor": "ui"
}
cpptools version (native): 1.30.5.0
Current database path: C:\USERS\HUANGQINJIN\APPDATA\LOCAL\MICROSOFT\VSCODE-CPPTOOLS\90D20250051651E1D809C1C7E0C52070\.BROWSE.VC.DB
Translation Unit Mappings:
[ C:\tmp\main.cpp - source TU]:
Translation Unit Configurations:
[ C:\tmp\main.cpp ]
    Process ID: 24416
    Memory Usage: 51 MB
    Compiler Path: C:\Program Files\LLVM\bin\clang-cl.exe
    Include paths:
        system include: C:\Program Files\LLVM\lib\clang\21\include
        system include: C:\tmp\.vscode
        system include: C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Tools\MSVC\14.50.35717\include
        system include: C:\Program Files\Microsoft Visual Studio\18\Enterprise\VC\Tools\MSVC\14.50.35717\atlmfc\include
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\ucrt
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\shared
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\um
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\winrt
        system include: C:\Program Files (x86)\Windows Kits\10\Include\10.0.26100.0\cppwinrt
    Standard Version: c++14
    IntelliSense Mode: windows-clang-x64
    Other Flags:
        --clang
        --clang_version=210108
        --ms_compatibility
Total Memory Usage: 51 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 6459
Number of files parsed: 1

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