nixos/filesystems: don't silently ignore label when device is set

Before this change, when both device and label were set, the label would
be silently ignored. This is especially problematic when the device is
set in another module, and it's not immediately obvious why the label is
not having any effect.

Additionally, some other modules use the device option to get the device
of a filesystem, but this option is not populated when only the label is
set, causing those modules to conclude that the filesystem does not have
a backing device.

With this change, we populate the device option using the label when the
label is set. This means that we get a clear error message when both the
device and label are set, and that the device is properly populated
whenever the label is used to specify the backing device.

0 files changed, 0 insertions, 0 deletions