In the case of D841, the interface file changes are very minor (specifically, a new tag is used when an empty closed type family is compiled, but of course none of them exist yet). Thus you might be able to get away without a full rebuild. Good point. Sadly, your patch conflicts with my work on injective type families so looks like I have no choice but to do a full rebuild. I'll post comments about things I wanted to test on Phab.
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