Install build and test dependencies

git checkout master && \
sudo apt install \
   devscripts \
   dh-make-perl \
   libdist-zilla-app-command-authordebs-perl && \
dzil authordebs --install && \
git checkout debian && \
mk-build-deps -i -r --root-cmd sudo

Update POT and PO files

git checkout master && \
    ( cd po && make pot && make update-po ) && \
    git add po && \
    git commit -m 'Update POT and PO files.'

Make an upstream release

git checkout master

Enable new translations in po/PACKAGE and commit.

Export new upstream version number:

export VERSION=XXX

Update version number in lib/Tails.pm, commit all files that need to be, run the upstream test suite, build an upstream tarball, tag the release, move the tarball out of the build repository and clean it up:

perl -pi -E 's,^Version [0-9.]+,Version $ENV{VERSION},' lib/Tails.pm && \
   perl -pi \
      -E "s,^our \\\$VERSION = '[0-9.]+';\$,our \\\$VERSION = '$VERSION';," \
      lib/Tails.pm && \
   git commit lib/Tails.pm -m "Tails-perl5lib $VERSION" && \
   RELEASE_TESTING=1 dzil test && \
   dzil build && \
   git tag -s "Tails-perl5lib_$VERSION" -m "Tails-perl5lib $VERSION" && \
   mv Tails-perl5lib-*.tar.gz .. && \
   git clean -fdx

Update the Debian package

Checkout the branch with Debian package specifics, import the new upstream tarball, update debian/changelog:

git checkout debian && \
   gbp import-orig --upstream-vcs-tag=Tails-perl5lib_$VERSION \
      ../Tails-perl5lib-$VERSION.tar.gz && \
   gbp dch --auto --spawn-editor=always

(Do not forget to set the appropriate release.)

Update the packaging (e.g. look at changes in dist.ini), and then update debian/changelog again if needed.

Commit debian/changelog:

    git commit debian/changelog \
        -m "$(echo "$(dpkg-parsechangelog -SSource) ($(dpkg-parsechangelog -SVersion))\n\nGit-Dch: Ignore\n")"

Build a Debian package (use a Stretch/amd64 chroot with stretch-backports enabled):

gbp buildpackage

If everything is fine, add a signed tag to the repository and push the changes:

gbp buildpackage --git-tag-only --git-sign-tags && \
git push --follow-tags origin \
                master:master \
                debian:debian \
                pristine-tar:pristine-tar \
                upstream:upstream

(Make sure master, upstream, debian and pristine-tar were all pushed.)

Add the Debian package to Tails

Sign the package:

debsign $CHANGES_FILE

Upload:

dupload --to tails $CHANGES_FILE