Dear Maintainer,

your package depends on libeigen3-dev. The upstream released a
new major version of this mathematical library, 5.0.0. Some
basic information about new features and changes in this version
can be found here:

https://libeigen.gitlab.io/releases/5.0/

This is a major version change and may require code changes in packages
depending on eigen3. The key breaking changes include:

  - Minimum required C++ standard is now C++14
  - Changes in the build system integration
  - Some API name changes

gnuplot-iostream FTBFS with libeigen3-dev 5.0.1. The full build log is available at:

https://debusine.debian.net/debian/developers-gladk-eigen3/artifact/3755978/

Here is the most probably relevant part of the failing build log:
    ===========================================
gnuplot-iostream.h:1598:31:   required from ‘void gnuplotio::PlotGroup::add(const T&, const std::string&, const std::string&, OrganizationMode) [with T = std::tuple<Eigen::Matrix<double, -1, -1, 0, -1, -1>, Eigen::Matrix<double, -1, -1, 0, -1, -1>, Eigen::Matrix<double, -1, -1, 0, -1, -1> >; OrganizationMode = gnuplotio::Mode2D; std::string = std::__cxx11::basic_string<char>]’
 1598 |             plots.emplace_back(arg, plotspec,
      |             ~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
 1599 |                 "array", // arbitrary value
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
 1600 |                 OrganizationMode(), ModeText());
      |                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
gnuplot-iostream.h:1575:154:   required from ‘gnuplotio::PlotGroup& gnuplotio::PlotGroup::add_plot2d(const T&, const std::string&, const std::string&) [with T = std::tuple<Eigen::Matrix<double, -1, -1, 0, -1, -1>, Eigen::Matrix<double, -1, -1, 0, -1, -1>, Eigen::Matrix<double, -1, -1, 0, -1, -1> >; std::string = std::__cxx11::basic_string<char>]’
 1575 |     template <typename T> PlotGroup &add_plot2d         (const T &arg, const std::string &plotspec="", const std::string &text_array_record="text") { add(arg, plotspec, text_array_record, Mode2D      ()); return *this; }
      |                                                                                                                                                       ~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
example-data-2d.cc:337:25:   required from here
  337 |         plots.add_plot2d(std::tuple{ptsx, ptsy, ptsz}, "with lines title 'tuple<eigen, eigen, eigen>'");
      |         ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
gnuplot-iostream.h:1390:41: error: static assertion failed: container not deep enough
 1390 |     static_assert(ArrayTraits<T>::depth >= Depth, "container not deep enough");
      |                                   ~~~~~~^~~~~~~~
gnuplot-iostream.h:1390:41: note: the comparison reduces to ‘(1 >= 2)’
gnuplot-iostream.h: In instantiation of ‘class gnuplotio::IteratorRange<void, double>’:
gnuplot-iostream.h:883:73:   required from ‘class gnuplotio::PairOfRange<gnuplotio::PairOfRange<gnuplotio::IteratorRange<void, double>, gnuplotio::IteratorRange<void, double> >, gnuplotio::IteratorRange<void, double> >’
  883 |     typedef std::pair<typename RT::value_type, typename RU::value_type> value_type;

    ===========================================
libeigen3-dev_5.0.1-1 is available in experimental.

When this package version lands into unstable (probably at the beginning
of June 2026), this bug will be increased in severity to serious.

Thanks,

Anton