[libc++] `codecvt<wchar_t, char, mbstate_t>::do_in` returns `ok` but not `partial` when having incompletely parsed UTF-8 input

[debugee]

sample

debug config

launch.json

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "type": "lldb",
            "request": "launch",
            "name": "Launch",
            "program": "${workspaceFolder}/build/testcpp",
            "args": [],
            "cwd": "${workspaceFolder}",
            "initCommands": [
                "settings set target.process.thread.step-avoid-regexp \"\"",
            ],
            "console": "integratedTerminal",
            "env": {
                "LANG":"en_US.UTF-8"
            }
        }
    ]
}

please add "LANG":"en_US.UTF-8"

in file locale.cpp
codecvt<wchar_t, char, mbstate_t>::do_in

llvm-project/libcxx/src/locale.cpp

Line 1416 in a9843ac

codecvt<wchar_t, char, mbstate_t>::result codecvt<wchar_t, char, mbstate_t>::do_in(

have bug when trans utf-8 to wchar_t

when input 你123

do_in trans uncompleted utf-8 bytes with first byte 0xe4
and return ok, but correct is partial

so bug come out

[llvmbot]

@llvm/issue-subscribers-c-1

Author: debugee (debugee)

sample

debug config

launch.json
{
// Use IntelliSense to learn about possible attributes.
// Hover to view descriptions of existing attributes.
// For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
"version": "0.2.0",
"configurations": [
{
"type": "lldb",
"request": "launch",
"name": "Launch",
"program": "${workspaceFolder}/build/testcpp",
"args": [],
"cwd": "${workspaceFolder}",
"initCommands": [
"settings set target.process.thread.step-avoid-regexp """,
],
"console": "integratedTerminal",
"env": {
"LANG":"en_US.UTF-8"
}
}
]
}

please add "LANG":"en_US.UTF-8"

<img width="714" alt="Image" src="https://github.com/user-attachments/assets/2870f4bd-9fe4-46d7-9b07-0ec0469efeb8" />

in file locale.cpp
codecvt<wchar_t, char, mbstate_t>::result codecvt<wchar_t, char, mbstate_t>::do_in(

have bug when trans utf-8 to wchar_t

when input 你123

do_in trans uncompleted utf-8 bytes with first byte 0xe4
and return ok, but correct is partial

so bug come out

[EugeneZelenko]

Which STL implementation do you use? Could you please create reproducer on https://godbolt.org?

[debugee]

Which STL implementation do you use? Could you please create reproducer on https://godbolt.org?

maybe all version of libc++ have bug

I compile llvm => tag: llvmorg-20.1.0

[frederick-vs-ja]

Thanks for reporting! I edited the title and description for descriptiveness and readability.