Deducing this (Explicit object member functions) not supported for conversion operators

[lukas-lang]

Environment

• OS and Version: Windows 11, 25H2
• VS Code Version: 1.108.1
• C/C++ Extension Version: 1.29.3
• If using SSH remote, specify OS of remote machine: N/A

Bug Summary and Steps to Reproduce

Bug Summary:
Deducing this is not supported for conversion operators, and instead results in a series of errors being reported

Steps to reproduce:

1. Set the C++ version to C++23
2. Create a file with the following content:

   auto ftm = __cpp_explicit_this_parameter;
   
   struct foo
   {
       auto bar(this auto &&self)
       {
           return 1;
       }
   
       operator int(this auto &&self)
       {
           return 1;
       }
   };
   
   int main()
   {
       int bar = foo{};
       
       return foo{}.bar();
   }
   

3. Observe the errors in the problems panel
   Expected behavior: No errors
   Observed behavior: There are 3 errors reported

an operator name must be declared as a function C/C++(501)
expected a ';' C/C++(65)
no suitable conversion function from "foo" to "int" exists C/C++(413)

Configuration and Logs

## Settings
`"C_Cpp.default.cppStandard": "c++23"`
## C/C++: Log Diagnostics
-------- Diagnostics - 1/19/2026, 10:59:49 AM
Version: 1.29.3
Current Configuration:
{
    "name": "Win32",
    "includePath": [
        "${workspaceFolder}/**"
    ],
    "defines": [
        "_DEBUG",
        "UNICODE",
        "_UNICODE"
    ],
    "compilerPath": "cl.exe",
    "cStandard": "c17",
    "intelliSenseMode": "windows-msvc-x64",
    "compilerPathInCppPropertiesJson": "cl.exe",
    "cppStandard": "c++23",
    "intelliSenseModeIsExplicit": false,
    "cStandardIsExplicit": false,
    "cppStandardIsExplicit": true,
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPathIsExplicit": false,
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.default.cppStandard": "c++23",
    "C_Cpp.loggingLevel": "Debug"
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": false,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "*.bsh": "java",
        "*.m": "matlab",
        "*.tr": "wolfram"
    },
    "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): 1.29.2.0
Current database path: C:\USERS\LUKAS\APPDATA\LOCAL\TEMP\{117CBE87-EFA1-445B-BCF0-1BA778E337A1}\.BROWSE.VC.DB
Translation Unit Mappings:
[ C:\Users\Lukas\Downloads\test.cpp - source TU]:
Translation Unit Configurations:
[ C:\Users\Lukas\Downloads\test.cpp ]
    Process ID: 5212
    Memory Usage: 59 MB
    Compiler Path: C:\Program Files\Microsoft Visual Studio\18\Community\VC\Tools\MSVC\14.50.35717\bin\Hostx64\x64\cl.exe
    Include paths:
        system include: C:\Program Files\Microsoft Visual Studio\18\Community\VC\Tools\MSVC\14.50.35717\include
    Defines:
        _DEBUG
        UNICODE
        _UNICODE
    Standard Version: ms_c++23
    IntelliSense Mode: windows-msvc-x64
Total Memory Usage: 59 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 263

Other Extensions

Note that MSVC 17.2 and later has no problem with the code (when removing the feature test macro): https://godbolt.org/z/qvMcbGd3b

Additional context

No response

[sean-mcmanus]

@lukas-lang It's a bug with our EDG compiler used for IntelliSense parsing.

[sean-mcmanus]

I filed internal issue 2687124.