Upstream paraview source and VTK submodule
==========================================

Paraview source is tightly bound to a given version of VTK.
Unfortunately paraview releases are not synchronised with VTK
releases. Paraview source therefore provides its own subdirectory
contain a copy of the required VTK source.

In the upstream paraview git repository at
https://gitlab.kitware.com/paraview/paraview
the VTK source is managed as a git submodule pointing to a specific
commit in the VTK upstream source at https://gitlab.kitware.com/vtk/vtk

Paraview no longer provides release tarballs. The last version at
https://gitlab.kitware.com/paraview/paraview/-/releases is v5.8.0

The paraview git repo does provide tarballs from all tags at
https://gitlab.kitware.com/paraview/paraview/-/tags
However these tarballs are automatically generated by git archive.
git archive does not include submodules in the generated tarball, so
the required VTK source is missing.

To work around these issues, debian maintainers now have to generated
the upstream source tarball manually after pulling the submodules.
The used method is suggested at
https://stackoverflow.com/a/67389978/12401525

The steps are
1) Clone the upstream repository
2) Checkout the desired tag (to obtain a specific release version)
3) Pull the submodules.
4) Generate a tarball including submodule source.

For instance, to obtain v5.11.2 source including submodules as
paraview-v5.11.2+dfsg.tar.gz:

UPSTREAM_TAG=v5.11.2
git clone https://gitlab.kitware.com/paraview/paraview.git
cd paraview
git checkout ${UPSTREAM_TAG}
git submodule update --init --recursive
git ls-files --recurse-submodules | tar caf ../paraview-${UPSTREAM_TAG}+dfsg.tar.gz -T-
