48_sphinx4_error.diff already does what this patch should do.

Fix test error in C++ template syntax. Closes: #984049

Closes: #980630

spelling-error-in-changelog handle handle (duplicate word) handle

Drop --with python3 and replace b-d on dh-python with a b-d on
dh-sequence-python3.

Drop override_dh_installdocs-indep in debian/rules.
Add b-d on debhelper (>= 12.5).

Fix systems already upgraded from << -3 to <= -6 by deleting the symlink
/usr/share/doc/libvigraimpex-dev/html and moving
/usr/share/doc/libvigraimpex-doc/html to
/usr/share/doc/libvigraimpex-dev in libvigraimpex-doc.preinst.

1.11.1+dfsg-3 replaced the symlink /usr/share/doc/libvigraimpex-doc/html
with a directory (introduced as part of DH 12 upgrade). Use
debian/libvigraimpex-doc.maintscript to properly handle handle upgrads
from << 1.11.1+dfsg3. (Thanks, Andreas Beckmann!) Closes: #950111

When overriding optimization levels for specifi tests append new -O options
instead of replacing it.

B-d on python3-dev instead of python3-all-dev since only the pythomn
module for the default python version is built. (Thanks, Sebastiaan
Couwenberg!)

it is not used anymore.

Revamp rules, use dh sequencer. Install docs from installed (debian/tmp)
instead of built directory.