In my case:
[curt:misc]$ mdls -name kMDItemContentTypeTree U.scala
kMDItemContentTypeTree = (
"dyn.ah62d4rv4ge81g25brvuu",
"public.item",
"dyn.ah62d4rv4ge81g25brvuu",
"public.data"
)
public.source-code is not in the list. How can I add it to the list of Content Types?