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

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

https://debusine.debian.net/debian/developers-gladk-eigen3/artifact/3757436/

Here is the most probably relevant part of the failing build log:
    ===========================================
-- Found OpenMP_CXX: -fopenmp (found version "4.5")
CMake Error at src/cmake/meshlab_tools.cmake:93 (_message):
  Eigen is required - at least one of VCG_ALLOW_SYSTEM_EIGEN or
  VCG_ALLOW_BUNDLED_EIGEN must be enabled and found.
Call Stack (most recent call first):
  src/vcglib/CMakeLists.txt:42 (message)

Dear maintainers,

eigen3 5.0 (libeigen3-dev 5.0) is now in unstable, so these FTBFS bugs are
release-critical.  I am therefore raising their severity to serious.

Regards,

Anton