c++: getline argument list type infered as std::ifstream instead of std::ifstream&?

class TextQuery
{
public:
    using line_no = std::vector<std::string>::size_type;
    TextQuery(std::ifstream&);
    QueryResult query(const std::string&) const;
private:
    std::shared_ptr<std::vector<std::string>> file;
    std::map<std::string, std::shared_ptr<std::set<line_no>>> vm;
};

TextQuery::TextQuery(std::ifstream &is): file(new std::vector<std::string>)
{
    std::string text;
    while (std::getline(is, text)) {
        file->push_back(text);
        int n = file->size() - 1;
        std::istringstream line(text);
        std::string word;
        while (line >> word) {
            auto& lines = vm[word];
            if (!lines) {
                lines.reset(new std::set<line_no>);
            }
            lines->insert(n);
        }
    }
}

IDE: visual studio 2019 error line:

while (std::getline(is, text)) {

the IDE inferred the argument list types of the getline function is "std::ifstream, std::string". so this is inconsistent with the signature of the getline (string) function. but is parameter is from function parameter which has type of "std::ifstream &". I am confused here why IDE infer it as "std::ifstream" instead of "std::ifstream &" ? can anybody give some thoughts about how to fix this?