Flatpak is the new name of xdg-app. So following up on my previous LibreOffice in a Box post, here is some more technical detail on how an upcoming LibreOffice 5.2 will be available as a Flatpak bundle.
There is now a shell script demonstrating how to do all the downloading of sources, building, and bundling up. I decided against using flatpak-builder (nee xdg-app-builder) for that mostly out of convenience, mainly because the way LibreOffice fetches its external dependencies is so different from the typical way of building a Linux app. So I felt more comfortable doing these things manually, calling the raw xdg-app build steps from a script. But given enough pressure (e.g., to make the LibreOfficeKit widget buried within the LibreOffice installation set available to other Flatpak apps), this might get revisited.
The script proceeds in six steps (see the above link for details):
First, building LibreOffice requires an Archive-Zip Perl module not found in the org.gnome.Sdk we build against. The easiest solution (easier than to try and get rid of that Perl dependency in the LibreOffice build machinery, that is) is to download it and make it available to the build via the PERLLIB environment variable.
Second, we need the LibreOffice sources themselves. The current master branch has all the necessary changes needed for a Flatpak’ed LibreOffice (as will the coming libreoffice-5-2 branch).
Third, we need to fetch LibreOffice’s external dependencies. LibreOffice has a long list of external projects that it can either use from the underlying system or build/bundle itself. Those external projects covered by Flatpak’s org.gnome.Platform runtime are taken from there, but whatever remains is bundled with the LibreOffice app. The sources for these external projects are normally downloaded during the build, but an xdg-app build does not have network connectivity, so they need to be downloaded upfront. So bootstrap enough of a LibreOffice build here to execute the
make fetch part.
Fourth, LibreOffice is built in xdg-app. The choice of building against the org.gnome.Platform 3.20 is somewhat arbitrarty, but it’s the latest revision available. And given LibreOffice’s strong GTK3 support (which e.g. also enables running on Wayland), this should make the resulting app more versatile than basing it on the more fundamental org.freedesktop.Platform. Building LibreOffice doesn’t exactly follow the
make && make install mantra, but there happened to already be a
make distro-pack-install target that produces the build artifacts in (almost) the right way for our purposes here.
Fifth, the build artifacts from the previous step are assembled in the way xdg-app expects them. Some of the metadata desktop and icon files need to be renamed, to match xdg-app’s expectation that metadata files belonging to the org.libreoffice.LibreOffice app have names actually starting with “org.libreoffice.LibreOffice”.
Finally, everything is bundled up into a LibreOffice.flatpak that can be distributed to users, who can then install it with
xdg-app install --bundle LibreOffice.flatpak.
The bundle contains all the available LibreOffice localizations. It doesn’t make that much of a difference for the size of the resulting LibreOffice.flatpak, and should be easier to handle for both producers and consumers than to provide dedicated single-language apps. For reasons of size, the help content is not bundled, though; the intent is to (transparently) use the online help content. However, one caveat with the current state of xdg-app is that an app cannot reach out to other applications on the machine via xdg-open (a portal will be needed for that). When asked to process “external” URLs (e.g., when clicking on a hyperlink in a text document, but also when accessing the online help), LibreOffice tries to pass those URLs to xdg-open, but that doesn’t work yet in xdg-app.