Function userdata_remapper_wrap 

pub unsafe extern "C" fn userdata_remapper_wrap(
    l: *mut lua_State,
    str: *const c_char,
    len: usize,
) -> u8

C trampoline installed into global_State::ecb.gettypemapping so the VM’s bytecode loader can map userdata type names through the registered remapper.

Mirrors userdataRemapperWrap (CodeGen/src/CodeGenContext.cpp):

static uint8_t userdataRemapperWrap(lua_State* L, const char* str, size_t len) {
    if (BaseCodeGenContext* codegenCtx = getCodeGenContext(L)) {
        uint8_t index = codegenCtx->userdataRemapper(codegenCtx->userdataRemappingContext, str, len);
        if (index < (LBC_TYPE_TAGGED_USERDATA_END - LBC_TYPE_TAGGED_USERDATA_BASE))
            return LBC_TYPE_TAGGED_USERDATA_BASE + index;
    }
    return LBC_TYPE_USERDATA;
}

Safety

l must be a valid lua_State pointer (or null, which is handled). This is invoked by the VM through a function pointer, hence extern "C".