Meld in master has ‘support’ for being built as an xdg-app bundle. This hasn’t actually required any changes to Meld itself, just a script or two to do the necessary building + shims.

If you want to build your own bundle, you can clone current Meld from git, and then:

sh Build an xdg-app bundle
mkdir meld-repo && mkdir appdir
cd meld
xdg-app-builder --repo=../meld-repo ../appdir data/org.gnome.meld-devel.json
cd ..
xdg-app --user remote-add --no-gpg-verify meld-repo meld-repo
xdg-app --user install meld-repo org.gnome.meld

Yes, this will download another copy of Meld from git, even though you just cloned it. Don’t think about it too much. This is just the result of me not properly understanding the xdg-app building model when I started, and the building model being a little odd. I’m sure there is (or will be) a sane way to keep xdg-app building info and scripts in the repo you’re building, but for now this appears to basically work.