Schema evolution for sets

Summary:
This diff provides the bare minimum schema evolution to allow set types to be used in production.

My plan is to provide much more elaborate evolution in future diffs. But because sets are implemented as syscalls, and the schema machinery currently doesn't use syscalls, such a change is pretty involved.

Reviewed By: donsbot, simonmar

Differential Revision: D65896602

fbshipit-source-id: da82f01a1febbaf6f9a58432741ee066e5fa2590

glean/db/Glean/Query/Transform.hs

@@ -483,7 +483,8 @@ transformTerm inner defaultForType src dst = go src dst
             (recurse discard)
             a
           _ -> error $ "expected Array, got " <> show term
-
+    go (SetTy from) (SetTy to)
+      | from == to = Nothing
     go (RecordTy from) (RecordTy to) =
       let transformations = transformationsFor from to
           sameFieldCount = length from == length to

glean/hs/Glean/Schema/Evolve.hs

@@ -376,6 +376,12 @@ canEvolve types compatible new old = go new old
     go StringTy StringTy = Nothing
     go BooleanTy BooleanTy = Nothing
     go (ArrayTy new) (ArrayTy old) = go new old
+    go (SetTy new) (SetTy old)
+      | new == old = Nothing
+      | otherwise = Just $ Text.pack $
+        "types inside sets cannot evolve. Type changed from " <>
+        show (displayDefault (SetTy old))
+        <> " to " <> show (displayDefault new)
     go (PredicateTy new) (PredicateTy old)
       | not (compatible new old) = Just
           $ "type changed from " <> showRef old
@@ -421,6 +427,7 @@ canEvolve types compatible new old = go new old
           BooleanTy -> True
           ByteTy -> True
           ArrayTy _ -> True
+          SetTy _ -> True
           RecordTy fields -> all (hasDefault . fieldDefType) fields
           EnumeratedTy{} -> True
           SumTy (first : _) -> hasDefault (fieldDefType first)