Bugfix: Diff calculation was detecting updates where there were not any.

Diff calculation did not check if values changed when a key is in
both maps that are being diffed. This means that it was detecting an
update, while in fact the value had not changed.

anti-diff/src/Data/Map/Diff/Strict.hs

@@ -158,13 +158,16 @@ nonEmptyDiffHistory (DiffHistory sq) = NEDiffHistory <$> NESeq.nonEmptySeq sq
 ------------------------------------------------------------------------------}
 
 -- | Compute the difference between @'Values'@.
-diff :: Ord k => Values k v -> Values k v -> Diff k v
+diff :: (Ord k, Eq v) => Values k v -> Values k v -> Diff k v
 diff (Values m1) (Values m2) = Diff $
     Merge.merge
       (Merge.mapMissing $ \_k v -> singletonDelete v)
       (Merge.mapMissing $ \_k v -> singletonInsert v)
       (Merge.zipWithMaybeMatched $ \ _k v1 v2 ->
-        Just $ singletonDelete v1 `unsafeMappend` singletonInsert v2
+        if v1 == v2 then
+          Nothing
+        else
+          Just $ singletonDelete v1 `unsafeMappend` singletonInsert v2
       )
       m1
       m2

ouroboros-consensus/src/Ouroboros/Consensus/Ledger/Basics.hs

@@ -676,7 +676,7 @@ applyLedgerTablesDiffsTicked = flip (zipOverLedgerTablesTicked $ flip rawApplyDi
 -- Calculate differences
 
 rawCalculateDifference ::
-     Ord k
+     (Ord k, Eq v)
   => ValuesMK   k v
   -> ValuesMK   k v
   -> TrackingMK k v