Building gnome builder from gnome builder fails because llvm flatpak extension is not installed
When trying to build gnome builder from gnome builder on the latest nightly the build exits very early on with the following error:
error: Requested extension org.freedesktop.Sdk.Extension.llvm12 not installed
This has something to do with changes to flatpak itself as far as I can gather from #1458 (closed). It seems there is also another issue related to this already #1486 (closed).
Because it took a bit of digging in these issues to figure out how to get my own build working again I thought it would be useful to have an issue dedicated specifically to the build error and a way to work around the issue.
Workaround:
flatpak remote-add flathub-beta https://flathub.org/beta-repo/flathub-beta.flatpakrepo
flatpak install flathub-beta org.freedesktop.Sdk.Extension.llvm12