fix[test]: quickcheck-instances panics when creating empty arrays

hon.cabal

@@ -19,6 +19,7 @@ extra-source-files:
 
 library
   exposed-modules:
+      Data.Array.Arbitrary
       Language.Json
       Language.Json.Parser
       Language.Json.Path

src/Data/Array/Arbitrary.hs

@@ -0,0 +1,22 @@
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE InstanceSigs #-}
+{-# LANGUAGE FlexibleContexts #-}
+module Data.Array.Arbitrary (ArbitraryArray(..), get) where
+import Test.QuickCheck (Arbitrary (arbitrary), Gen)
+import Data.Array.IArray (listArray, IArray, Ix)
+import Data.List (genericLength)
+
+newtype ArbitraryArray a i e = ArbitraryArray { getArbitraryArray :: a i e }
+  deriving stock (Show)
+
+get :: ArbitraryArray a i e -> a i e
+get = getArbitraryArray
+
+instance (Arbitrary e, Num i, Ix i, IArray a e) => Arbitrary (ArbitraryArray a i e) where
+  arbitrary :: Gen (ArbitraryArray a i e)
+  arbitrary = do
+    xs <- arbitrary
+    pure . ArbitraryArray $ case xs of
+      [] -> listArray (1, 0) xs
+      _  -> listArray (0, genericLength xs - 1) xs
+

src/Language/Json.hs

@@ -28,8 +28,7 @@ import GHC.Generics ( Generic, Generically(..) )
 import Pretty.Serialize (PrettySerialize)
 import Test.QuickCheck (Arbitrary (arbitrary), Gen, UnicodeString (getUnicodeString), PrintableString (getPrintableString))
 import qualified Test.QuickCheck.Gen as Gen
-import Test.QuickCheck.Instances.Array ()
+import Data.Array.Arbitrary (ArbitraryArray(getArbitraryArray))
-import Test.QuickCheck.Instances.Natural ()
 
 
 data Value
@@ -50,7 +49,7 @@ instance Arbitrary Value where
     , String . Text.pack . getUnicodeString <$> arbitrary
     , Boolean <$> arbitrary
     , Number <$> arbitrary
-    , Array <$> Gen.scale (`div` 2) arbitrary
+    , Array . getArbitraryArray <$> Gen.scale (`div` 2) arbitrary
     , Object . Map.mapKeys (Text.pack . getUnicodeString) <$> Gen.scale (`div` 2) arbitrary
     ]
 
@@ -64,7 +63,7 @@ instance Arbitrary PrintableValue where
     , String . Text.pack . getPrintableString <$> arbitrary
     , Boolean <$> arbitrary
     , Number <$> arbitrary
-    , Array <$> Gen.scale (`div` 2) arbitrary
+    , Array . getArbitraryArray <$> Gen.scale (`div` 2) arbitrary
     , Object . Map.mapKeys (Text.pack . getPrintableString) <$> Gen.scale (`div` 2) arbitrary
     ]