Natvis: Size specifier for array-like structures is not working

Environment

• OS and version: Linux
• VS Code: 1.85.2
• C/C++ extension: 1.18.5
• OS and version of remote machine (if applicable): RHEL 7.6
• GDB / LLDB version: 10.2

Bug Summary and Steps to Reproduce

Bug Summary:

In my natvis file, I am trying to create a visualizer for GCC's std::string_view, and I am using a method similar to how MSVC displays their std::string_view. It looks like so:

<Type Name="std::string_view">
    <AlternativeType Name="std::basic_string_view&lt;*,*&gt;" />
    <DisplayString>{_M_str,[_M_len]na}</DisplayString>
    <StringView>_M_str,[_M_len]na</StringView>
    <Expand>
        <Item Name="[size]" ExcludeView="simple">_M_len</Item>
        <ArrayItems ExcludeView="simple">
            <Size>_M_len</Size>
            <ValuePointer>_M_str</ValuePointer>
        </ArrayItems>
    </Expand>
</Type>

During debugging, the DisplayString just reports "-var-create: unable to create variable object".

If I remove the size specifier, it works, but this isn't correct because a std::string_view doesn't necessarily need to be a null-terminated string.

Steps to reproduce:

1. Start a remote debugging session to a linux server (haven't tried this with running directly on my linux machine)
2. Use a custom natvis file with the above std::string_view visualizer
3. Create a c++ program that uses std::string_view
4. Start a debugging session of a c++ application
5. Try to visualize the std::string_view and see the "-var-create" option

Debugger Configurations

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Attach MyProgram",
            "type": "cppdbg",
            "request": "attach",
            "program": "/path/to/my/program",
            "visualizerFile": "${workspaceFolder}/stl.natvis",
            "showDisplayString": true,
            "miDebuggerPath": "/usr/local/bin/gdb",
            "MIMode": "gdb"
        }
    ]
}

Debugger Logs

--> E (output): {"type":"event","event":"output","body":{"category":"console","output":"1: (31423) <-2235-var-create  - * \"((lPattern)._M_str),[((lPattern)._M_len)]na\"\n"},"seq":10547}
1: (31423) <-2235-var-create  - * "((lPattern)._M_str),[((lPattern)._M_len)]na"
--> R (variables-33): {"type":"response","request_seq":33,"success":true,"command":"variables","body":{"variables":[{"name":"lPattern","value":"-var-create: unable to create variable object","type":"std::string_view","evaluateName":"lPattern","variablesReference":1002},{"name":"lTagName","value":"0x7fffffff8130 \"\"","type":"std::string","evaluateName":"lTagName","variablesReference":1003},{"name":"lStatus","value":"0","type":"int","evaluateName":"lStatus","variablesReference":0,"memoryReference":"0x0000000000000000"},{"name":"lWaveAll","value":"false","type":"bool","evaluateName":"lWaveAll","variablesReference":0},{"name":"lTagFound","value":"false","type":"bool","evaluateName":"lTagFound","variablesReference":0},{"name":"lInsertPoint","value":"false","type":"bool","evaluateName":"lInsertPoint","variablesReference":0},{"name":"lTagCount","value":"1","type":"int","evaluateName":"lTagCount","variablesReference":0,"memoryReference":"0x0000000000000001"},{"name":"lRecursive","value":"0","type":"int","evaluateName":"lRecursive","variablesReference":0,"memoryReference":"0x0000000000000000"},{"name":"lDepth","value":"-1","type":"int","evaluateName":"lDepth","variablesReference":0},{"name":"lLimit","value":"5000","type":"int","evaluateName":"lLimit","variablesReference":0,"memoryReference":"0x0000000000001388"},{"name":"lCount","value":"false","type":"bool","evaluateName":"lCount","variablesReference":0},{"name":"lIsExtId","value":"false","type":"bool","evaluateName":"lIsExtId","variablesReference":0},{"name":"xPattern","value":"-var-create: unable to create variable object","type":"std::string_view","evaluateName":"xPattern","variablesReference":1004},{"name":"xOptions","value":"-var-create: unable to create variable object","type":"std::string_view","evaluateName":"xOptions","variablesReference":1005},{"name":"xFlush","value":"0","type":"int","evaluateName":"xFlush","variablesReference":0,"memoryReference":"0x0000000000000000"},{"name":"xRequest","value":"{...}","type":"const wave::AddWaveReq &","evaluateName":"xRequest","variablesReference":1006}]},"seq":10587}

Other Extensions

No response

Additional Information

No response

Inizia con il file natvis personalizzato e l’espressione ArrayItems Size mostrata nel report, quindi riproduci il malfunzionamento usando la configurazione GDB remoto e il log del debugger forniti. Traccia il modo in cui l’estensione C++ gestisce lo specificatore di dimensione natvis per la visualizzazione di string_view; il lavoro è completato quando il visualizzatore viene creato correttamente e visualizza i caratteri delimitati senza l’errore var-create.