Add failing test

Makefile

@@ -18,6 +18,9 @@ format: format-nix format-haskell
 ghcid: hpack
 	ghcid -c "cabal --ghc-options='${GHC_OPTIONS}' repl"
 
+ghcid-test: hpack
+	ghcid -c "cabal --ghc-options='${GHC_OPTIONS}' repl derive-has-field-test"
+
 hlint: hpack
 	hlint .
 
@@ -32,4 +35,4 @@ hackage: hpack
 	# cabal upload --publish dist-newstyle/sdist/derive-has-field-0.1.0.0.tar.gz
 	# cabal upload --publish -d dist-newstyle/derive-has-field-0.1.0.0-docs.tar.gz
 
-.PHONY: build hpack test run format-haskell format-nix format ghcid hlint bounds hackage
+.PHONY: build hpack test run format-haskell format-nix format ghcid ghcid-test hlint bounds hackage

src/DeriveHasField.hs

@@ -12,6 +12,7 @@ import Control.Monad
 import Data.Char (toLower)
 import Data.Foldable as Foldable
 import Data.Traversable (for)
+import Debug.Trace
 import GHC.Records
 import Language.Haskell.TH
 import Language.Haskell.TH.Datatype
@@ -23,7 +24,7 @@ makeDeriveHasField :: (String -> String) -> DatatypeInfo -> DecsQ
 makeDeriveHasField fieldModifier datatypeInfo = do
   -- We do not support sum of product types
   constructorInfo <- case datatypeInfo.datatypeCons of
-    [info] -> pure info
+    [info] -> trace (show datatypeInfo) $ pure info
     _ -> fail "deriveHasField: only supports product types with a single data constructor"
 
   -- We only support data and newtype declarations

test/DeriveHasFieldSpec.hs

@@ -26,6 +26,20 @@ someType =
     , someTypeSomeEitherField = Right 0
     }
 
+data OtherType a = OtherType
+  { otherTypeField :: Maybe a
+  , otherTypeOtherField :: Maybe a
+  }
+
+deriveHasFieldWith (dropPrefix "otherType") ''OtherType
+
+otherType :: OtherType Int
+otherType =
+  OtherType
+    { otherTypeField = Just 0
+    , otherTypeOtherField = Nothing
+    }
+
 spec :: Spec
 spec = do
   describe "deriveHasField" $ do
@@ -34,3 +48,6 @@ spec = do
       someType.someOtherField `shouldBe` 0
       someType.someMaybeField `shouldBe` Just 0
       someType.someEitherField `shouldBe` Right 0
+    it "compiles and gets the right field" $ do
+      otherType.field `shouldBe` Just 0
+      otherType.otherField `shouldBe` Nothing