(C++23) Fails to parse a particular lambda expression within an initializer list

[Motyak]

Environment

• OS and Version: Fedora Linux 42 (Workstation Edition)
• VS Code Version: 1.100.2
• C/C++ Extension Version: 1.25.3
• If using SSH remote, specify OS of remote machine: _

Bug Summary and Steps to Reproduce

Bug Summary:
Having a lambda expression that contains a front attribute, when inside an initializer list, triggers a syntax error.

Steps to reproduce:

1. Copy-paste this code snippet in a cpp file :

#include <vector>
#include <functional>

// example #1: works
std::function<void()> a = [] [[noreturn]] () {};

// example #2: works
auto b = std::function<void()>{[] () {}};

// example #3: doesn't work
auto c = std::function<void()>{[] [[noreturn]] () {}};

Expected behavior:
Based on this C++23 "spec" there should be no syntax error reported
-> https://en.cppreference.com/w/cpp/language/lambda.html
(see under Explanation > front-attr)
But even if the spec is wrong, it should at least stay consistent between example #1 and #3 (both fails or both pass)
(though g++ 15.1.1 parses it fine)

Configuration and Logs

{
    "configurations": [
        {
            "name": "Linux",
            "includePath": [
                "${workspaceFolder}/include",
                "${workspaceFolder}/monlang-parser/include",
            ],
            "defines": [],
            "compilerPath": "/usr/bin/g++",
            "cStandard": "c23",
            "cppStandard": "c++23",
            "intelliSenseMode": "linux-gcc-x64"
        }
    ],
    "version": 4
}

-------- Diagnostics - 6/3/2025, 9:28:25 AM
Version: 1.25.3
Current Configuration:
{
    "name": "Linux",
    "includePath": [
        "/home/motyak/devv/monlang-interpreter/include",
        "/home/motyak/devv/monlang-interpreter/monlang-parser/include"
    ],
    "defines": [],
    "compilerPath": "/usr/bin/g++",
    "cStandard": "c23",
    "cppStandard": "c++23",
    "intelliSenseMode": "linux-gcc-x64",
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPathInCppPropertiesJson": "/usr/bin/g++",
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.loggingLevel": "Debug",
    "C_Cpp.autoAddFileAssociations": false
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "*.cpp": "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,
        "monlang-LV1/*": true,
        "monlang-parser/*": true,
        "lib/monlang-LV1/*": true,
        "lib/monlang-LV2/*": true
    },
    "workbenchSettingsEditor": "ui"
}
cpptools version (native): 1.25.3.0
Current database path: /home/motyak/.cache/vscode-cpptools/d4fd19c9f7621ce3aa4ae46b901a0e1a/.browse.VC.db
Translation Unit Mappings:
[ /home/motyak/devv/monlang-interpreter/src/builtin/exit.cpp - source TU]:
Translation Unit Configurations:
[ /home/motyak/devv/monlang-interpreter/src/builtin/exit.cpp ]
    Process ID: 8917
    Memory Usage: 142 MB
    Compiler Path: /usr/bin/g++
    Include paths:
        include: /home/motyak/devv/monlang-interpreter/include
        include: /home/motyak/devv/monlang-interpreter/monlang-parser/include
        system include: /usr/include/c++/15
        system include: /usr/include/c++/15/x86_64-redhat-linux
        system include: /usr/include/c++/15/backward
        system include: /usr/lib/gcc/x86_64-redhat-linux/15/include
        system include: /usr/local/include
        system include: /usr/include
    Standard Version: c++23
    IntelliSense Mode: linux-gcc-x64
    Other Flags:
        --g++
        --gnu_version=150101
Total Memory Usage: 142 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 8560
Number of files parsed: 1130-------- Diagnostics - 6/3/2025, 9:28:25 AM
Version: 1.25.3
Current Configuration:
{
    "name": "Linux",
    "includePath": [
        "/home/motyak/devv/monlang-interpreter/include",
        "/home/motyak/devv/monlang-interpreter/monlang-parser/include"
    ],
    "defines": [],
    "compilerPath": "/usr/bin/g++",
    "cStandard": "c23",
    "cppStandard": "c++23",
    "intelliSenseMode": "linux-gcc-x64",
    "compilerPathIsExplicit": true,
    "cStandardIsExplicit": true,
    "cppStandardIsExplicit": true,
    "intelliSenseModeIsExplicit": true,
    "recursiveIncludesReduceIsExplicit": false,
    "recursiveIncludesPriorityIsExplicit": false,
    "recursiveIncludesOrderIsExplicit": false,
    "compilerPathInCppPropertiesJson": "/usr/bin/g++",
    "mergeConfigurations": false,
    "recursiveIncludes": {},
    "browse": {
        "limitSymbolsToIncludedHeaders": true
    }
}
Modified Settings:
{
    "C_Cpp.loggingLevel": "Debug",
    "C_Cpp.autoAddFileAssociations": false
}
Additional Tracked Settings:
{
    "editorTabSize": 4,
    "editorInsertSpaces": true,
    "editorAutoClosingBrackets": "languageDefined",
    "filesEncoding": "utf8",
    "filesAssociations": {
        "*.cpp": "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,
        "monlang-LV1/*": true,
        "monlang-parser/*": true,
        "lib/monlang-LV1/*": true,
        "lib/monlang-LV2/*": true
    },
    "workbenchSettingsEditor": "ui"
}
cpptools version (native): 1.25.3.0
Current database path: /home/motyak/.cache/vscode-cpptools/d4fd19c9f7621ce3aa4ae46b901a0e1a/.browse.VC.db
Translation Unit Mappings:
[ /home/motyak/devv/monlang-interpreter/src/builtin/exit.cpp - source TU]:
Translation Unit Configurations:
[ /home/motyak/devv/monlang-interpreter/src/builtin/exit.cpp ]
    Process ID: 8917
    Memory Usage: 142 MB
    Compiler Path: /usr/bin/g++
    Include paths:
        include: /home/motyak/devv/monlang-interpreter/include
        include: /home/motyak/devv/monlang-interpreter/monlang-parser/include
        system include: /usr/include/c++/15
        system include: /usr/include/c++/15/x86_64-redhat-linux
        system include: /usr/include/c++/15/backward
        system include: /usr/lib/gcc/x86_64-redhat-linux/15/include
        system include: /usr/local/include
        system include: /usr/include
    Standard Version: c++23
    IntelliSense Mode: linux-gcc-x64
    Other Flags:
        --g++
        --gnu_version=150101
Total Memory Usage: 142 MB

------- Workspace parsing diagnostics -------
Number of files discovered (not excluded): 8560
Number of files parsed: 1130

Other Extensions

No response

Additional context

No response

[sean-mcmanus]

@Motyak FYI, C++23 is still in development for our extension. 1.26.1 has more C++23 features added, but I haven't checked yet if this is one of them.

UPDATE: Doesn't work with 1.26.1.

[sean-mcmanus]

@Motyak I've filed a bug on our shared VS parser at https://developercommunity.visualstudio.com/t/Incorrect-IntelliSense-errors-occur-with/10915778

UPDATE: It looks like our EDG-based parser currently supports the new C++23 attributes on lambda feature according to https://en.cppreference.com/w/cpp/23.html, so this does seem likely to be an unintended bug and not a feature they haven't implemented yet.