Filters set in DesignSpace files are ignored

[khaledhosny]

A DesognSpace file with filters set in <variable-font> lib are ignored. I’m not sure if these filters are supposed to be processed or not, but in Glyphs filters are set on the instances, and variable font instances are mapped to DesignSpace <variable-font>.

The root of this issue is that *InterpolatablePreProcessor takes a list of UFO files as input, so we would need to get the <variable-font> to it somehow and load filters from it in additions to filters set on on the individual UFOs, or should it be done in a different way?

[anthrotype]

we would need to get the to it somehow and load filters from it in additions to filters set on on the individual UFOs

yeah. Possibly the caller could load the filters from the designspace and pass them on to the InterpolatablePreProcessor using its filters parameter.
depending on whether we want these filters from the designspace to override or extend, we have to either omit or add the ellipsis ... in the filters parameter.