The state dir is not on the same filesystem as the target dir
Submitted by Dag Odenhall
When trying to build any flatpak, Builder says,
The state dir (/home/.../Projects/.../.flatpak-builder) is not on the same filesystem as the target dir (/home/.../.cache/gnome-builder/flatpak/staging/...)
This seems to have started after an update to flatpak-builder, so it could be a flatpak issue rather than a Builder issue but Builder is where I'm seeing it and it seems to come about as a result of where Builder runs builds. I could report this against flatpak-builder as well or instead if you think that's more appropriate.
My ~/.cache is a separate Btrfs subvolume, because I'm using snapper to create snapshots of $HOME regularly and caches aren't important but tend to hold a lot of unique and changing data that would grow snapshots out of control, but it's all a single Btrfs filesystem.
As a result I'm effectively locked out of using Builder because I can't build any projects and there's no obvious workaround except moving ~/Projects to ~/.cache, and that's just silly.