First time setup

git clone git@gitlab-ssh.tails.net:tails/gnome-software
cd gnome-software
git remote add debian-upstream https://salsa.debian.org/gnome-team/gnome-software.git

Import new version

First make sure your checkout is up-to-date:

git fetch origin
git fetch debian-upstream

Let's say GNOME Software 51.1-1 hits Debian unstable, then set:

DEBIAN_TAG=debian/51.1-1
TAILS_ISSUE=12345

And derive these:

VERSION="${DEBIAN_TAG#*/}"~bpo13+0tails1
GNOME_SOFTWARE_BRANCH="tails/backport-${DEBIAN_TAG:?}"
TAILS_BRANCH="${TAILS_ISSUE:?}-gnome-software-${DEBIAN_TAG#*/}-backport"

Check for new Adwaita usage

GNOME Software 51 depends on libadwaita >= 1.8~alpha, but Trixie only has 1.7.6, and we don't want to backport a higher version. Therefore we have to monitor any changes we introduce with new version for new usage of libadwaita, and make sure it still works. As an example of something that does not work, but which we considers acceptable, commit 657bc3aa introduces AdwShortcutsSection which requires libadwaita >= 1.8, so in our backport this dialog doesn't work. For details, see this thread.

git log -p -GAdw origin/tails/trixie.."${DEBIAN_TAG:?}" -- src

Prepare new release

git checkout -b "${GNOME_SOFTWARE_BRANCH:?}" origin/tails/trixie
git merge "${DEBIAN_TAG:?}"

You likely will have to deal with merge conflicts in debian/changelog.

Then prepare the release:

(
set -eu -o pipefail
gbp dch --new-version="${VERSION:?}" --distribution="${TAILS_BRANCH:?}" --debian-branch="${GNOME_SOFTWARE_BRANCH:?}"
dch --append "Rebuild for Trixie"
git commit -m "releasing package gnome-software version ${VERSION}" debian/changelog
gbp buildpackage --git-tag-only --git-sign-tags --git-debian-branch="${GNOME_SOFTWARE_BRANCH:?}"
git show
)

Build Debian packages

For instance, if you use pbuilder:

gbp buildpackage --git-debian-branch="${GNOME_SOFTWARE_BRANCH:?}" --git-pbuilder --git-arch=amd64 --git-dist=trixie

Publish packaging branch

git push \
    --set-upstream \
    -o merge_request.create \
    -o merge_request.draft \
    -o merge_request.target=tails/trixie \
    -o merge_request.title="Draft: Backport ${DEBIAN_TAG}" \
    origin "${GNOME_SOFTWARE_BRANCH:?}"

Prepare Tails branch

(
set -eu -o pipefail
cd "${TAILS_GIT_REPO:?}"
git fetch origin
git checkout -b "${TAILS_BRANCH:?}" origin/stable
bin/add-APT-overlay --enable
)

Then update the value ignore.temporary.gnome-software.version in config/ci/needed-package-updates.yml to the version we just backported, as outputted by:

echo "${DEBIAN_TAG#*/}"

Next, publish the branch:

(
set -eu -o pipefail
git push \
    --set-upstream \
    -o merge_request.create \
    -o merge_request.draft \
    -o merge_request.target=stable \
    -o merge_request.title="Draft: Install GNOME Software ${VERSION:?}" \
    origin "${TAILS_BRANCH:?}"
bin/add-APT-overlay --wait
)

Upload Debian packages

Once the APT suite is ready (when the previous command finishes) you can upload the packages using dput or dupload (see this document for setup instructions).