Looking at the changelog for efl, the maintainer decided to give up on dev packages for the individual libraries and only provide one dev package ( libefl-all-dev ) for all the efl libraries. Transitional packages were provided for the buster release, but have now been dropped in bullseye/sid.
Thus the thing to do here is to change the build-dependency from libecore-dev to libefl-all-dev . I made this change locally and it test-built succesfully. I have decided to go ahead with a NMU and per the NMU guidelines to do so without delay. A debdiff is attatched to this mail.
diff -Nru dbus-c++-0.9.0/debian/changelog dbus-c++-0.9.0/debian/changelog --- dbus-c++-0.9.0/debian/changelog 2018-01-27 00:08:15.000000000 +0000 +++ dbus-c++-0.9.0/debian/changelog 2020-04-30 17:10:39.000000000 +0000 @@ -1,3 +1,11 @@ +dbus-c++ (0.9.0-8.2) unstable; urgency=medium + + * Non-maintainer upload. + * Change build-dependency from obsolete libecore-dev to libefl-all-dev + (Closes: 950619) + + -- Peter Michael Green <plugw...@debian.org> Thu, 30 Apr 2020 17:10:39 +0000 + dbus-c++ (0.9.0-8.1) unstable; urgency=medium * Non-maintainer upload. diff -Nru dbus-c++-0.9.0/debian/control dbus-c++-0.9.0/debian/control --- dbus-c++-0.9.0/debian/control 2015-08-21 06:38:59.000000000 +0000 +++ dbus-c++-0.9.0/debian/control 2020-04-30 17:10:39.000000000 +0000 @@ -11,7 +11,7 @@ dpkg-dev (>= 1.16.1), graphviz, libdbus-1-dev (>= 0.60), - libecore-dev, + libefl-all-dev, libexpat1-dev, libglib2.0-dev, libgtkmm-2.4-dev (>= 1:2.24.4-2~),
