Function RunFormatter

library/cpp/yt/string/format-inl.h:1129–1256

template <CFormatter TFormatter, class... TArgs>
void RunFormatter(
    TStringBuilderBase* builder,
    TBasicFormatString<TArgs...> formatString,
    const TFormatter& formatter)
{
    auto isValidLocations = [] (const auto& t) {
        return std::get<0>(t) != std::get<1>(t);
    };
    // Generally marker is simply "%v" e.g. 2 symbols.
    // We assume it is used to insert something for roughly 5 symbols
    // of size.
    builder->Preallocate(std::size(formatString.Get()) + sizeof...(TArgs) * (5 - 2));

    // Empty marker positions -- fallback to the normal impl.
    if constexpr (sizeof...(TArgs) != 0) {
        if (!isValidLocations(formatString.Markers[0])) {
            RunFormatterFullScan(builder, formatString.Get(), formatter);
            return;
        }
    } else {
        if (formatString.Escapes[0] == -2) {
            RunFormatterFullScan(builder, formatString.Get(), formatter);
            return;
        }
    }

    int escapesFound = 0;
    int currentPos = 0;

    auto beginIt = formatString.Get().begin();
    auto size = formatString.Get().size();

    const auto& [markers, escapes] = std::tie(formatString.Markers, formatString.Escapes);

    auto appendVerbatim = [&] (int offsetToEnd) {
        builder->AppendString(TStringBuf{beginIt + currentPos, beginIt + offsetToEnd});
    };

    auto processEscape = [&] () mutable {
        // OpenMP doesn't support structured bindings :(.
        auto escapePos = formatString.Escapes[escapesFound];

        // Append everything that's present until %%.
        appendVerbatim(escapePos);

        // Append '%'.
        builder->AppendChar('%');

        // Advance position to first '%' pos + 2.
        currentPos = escapePos + 2;
    };

    int argIndex = 0;

    while(argIndex < std::ssize(markers)) {
        auto [markerStart, markerEnd] = markers[argIndex];

        if (