Skip to content

Add support for clang-cl behavior for /external:I #14186

Open
Bug
Open
Add support for clang-cl behavior for /external:I#14186
Bug
Assignees
Colengms
Labels
Language Servicebugcompiler supportfixedCheck the Milestone for the release in which the fix is or will be available.
Milestone
1.35.2

Description

@huangqinjin
huangqinjin
opened on Feb 12, 2026

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

No activity

Activity on this issue will appear here.

Activity

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment

Metadata

Metadata

Assignees

Labels

Language Servicebugcompiler supportfixedCheck the Milestone for the release in which the fix is or will be available.

Type

Bug

Projects

  • cpptools
    Status
    Done

Milestone

Relationships

None yet

Development

No branches or pull requests

Issue actions