If we get an error from the message bus (dbus-daemon or dbus-broker),
for example ServiceUnknown if Avahi is not installed or perhaps
SpawnFailed if the service is disabled, it is mapped to a GLib GError.
The errors typically emitted by the message bus belong to the GDBusError
domain, but if nobody has registered the G_DBUS_ERROR domain yet,
then they might be mapped to G_IO_ERROR_DBUS_ERROR instead.
Previously, this code ignored G_IO_ERROR_DBUS_ERROR, but emitted a
warning if the error happens to have been mapped to G_DBUS_ERROR.
This resulted in action-at-a-distance: an unrelated component
triggering registration of the G_DBUS_ERROR domain would make printing
dialogs log the warning. This seems undesirable, and in particular it
can cause test failures, because GLib's test framework makes warnings
fatal by default.
Signed-off-by: Simon McVittie <smcv@debian.org>
9d9e665f34