Update FromJSON TickNumber instance to match ToJSON instance (#1870)

Fixes #1868.

src/swarm-engine/Swarm/Game/Tick.hs

@@ -12,15 +12,19 @@ import Data.Aeson qualified as A
 import Data.Int (Int64)
 import GHC.Generics (Generic)
 import Prettyprinter (Pretty (..))
+import Swarm.Util.JSON (optionsUnwrapUnary)
 import Swarm.Util.WindowedCounter (Offsettable (..))
 
 -- | A newtype representing a count of ticks (typically since the
 --   start of a game).
 newtype TickNumber = TickNumber {getTickNumber :: Int64}
-  deriving (Eq, Ord, Show, Read, Generic, FromJSON)
+  deriving (Eq, Ord, Show, Read, Generic)
 
 instance ToJSON TickNumber where
-  toJSON = A.genericToJSON (A.defaultOptions {A.unwrapUnaryRecords = True})
+  toJSON = A.genericToJSON optionsUnwrapUnary
+
+instance FromJSON TickNumber where
+  parseJSON = A.genericParseJSON optionsUnwrapUnary
 
 -- | Add an offset to a 'TickNumber'.
 addTicks :: Int -> TickNumber -> TickNumber

src/swarm-util/Swarm/Util/JSON.hs

@@ -0,0 +1,12 @@
+-- |
+-- SPDX-License-Identifier: BSD-3-Clause
+--
+-- Utilities for JSON de/serialization.
+module Swarm.Util.JSON where
+
+import Data.Aeson qualified as A
+
+-- | @aeson@ options specifying to unwrap unary records so they are
+--   encoded as a simple value instead of as a JSON object.
+optionsUnwrapUnary :: A.Options
+optionsUnwrapUnary = A.defaultOptions {A.unwrapUnaryRecords = True}

swarm.cabal

@@ -525,6 +525,7 @@ library swarm-util
     Data.BoolExpr.Simplify
     Swarm.Util
     Swarm.Util.Erasable
+    Swarm.Util.JSON
     Swarm.Util.Lens
     Swarm.Util.OccurrenceEncoder
     Swarm.Util.ReadableIORef