Merge pull request #1041 from haskell/issue-571

Add a regression test for issue #571

aeson.cabal

@@ -163,6 +163,7 @@ test-suite aeson-tests
     PropertyRTFunctors
     PropertyTH
     PropUtils
+    Regression.Issue571
     Regression.Issue967
     SerializationFormatSpec
     Types

tests/Regression/Issue571.hs

@@ -0,0 +1,23 @@
+{-# LANGUAGE OverloadedStrings, DeriveGeneric  #-}
+module Regression.Issue571 (issue571) where
+
+import Test.Tasty (TestTree)
+import Test.Tasty.HUnit (testCase, (@?=))
+import GHC.Generics (Generic)
+
+import Data.Aeson
+
+data F = F
+    { a :: Maybe Int
+    , b :: Maybe Int
+    }
+  deriving (Eq, Show, Generic)
+
+instance FromJSON F where
+    parseJSON = genericParseJSON defaultOptions { omitNothingFields = False } -- default
+
+issue571 :: TestTree
+issue571 = testCase "issue571" $ do
+    -- the Maybe fields can be omitted.
+    let actual = decode "{}" :: Maybe F
+    actual @?= Just F { a = Nothing, b = Nothing }

tests/UnitTests.hs

@@ -72,6 +72,7 @@ import qualified Data.Text.Lazy.Encoding as TLE
 import qualified ErrorMessages
 import qualified SerializationFormatSpec
 import qualified Data.Map as Map -- Lazy!
+import Regression.Issue571
 import Regression.Issue967
 
 roundTripCamel :: String -> Assertion
@@ -826,6 +827,7 @@ tests = testGroup "unit" [
       assertEqual "" (object ["foo" .= True]) [aesonQQ| {"foo": true } |]
     ]
   , monadFixTests
+  , issue571
   , issue967
   , testCase "KeyMap.insertWith" $ do
       KM.insertWith (-)        "a" 2 (KM.fromList [("a", 1)]) @?= KM.fromList [("a",1 :: Int)]