Fix, add tests

Author: m-bock

src/Data/Codec/Argonaut/Generic.purs

@@ -70,11 +70,12 @@ instance nullarySumCodecCtor ∷ IsSymbol name ⇒ NullarySumCodec (Constructor
       tagRaw = reflectSymbol (Proxy ∷ Proxy name)
       tag = encoding.mapTag tagRaw
     in
-      J.fromString $ tag
+      J.fromString tag
   nullarySumDecode encoding name j = do
-    tagRaw ← note (CA.Named name (CA.TypeMismatch "String")) (J.toString j)
-    let tag = encoding.mapTag tagRaw
-    if tag /= reflectSymbol (Proxy ∷ Proxy name) then
+    actualTag ← note (CA.Named name (CA.TypeMismatch "String")) (J.toString j)
+    let expectedTagRaw = reflectSymbol (Proxy ∷ Proxy name)
+    let expectedTag = encoding.mapTag expectedTagRaw
+    if expectedTag /= actualTag then
       Left (CA.Named name (CA.UnexpectedValue j))
     else
       Right (Constructor NoArguments)

test/Test/Generic.purs

@@ -2,14 +2,15 @@ module Test.Generic where
 
 import Prelude
 
-import Data.Codec.Argonaut.Generic (nullarySum)
+import Data.Codec.Argonaut.Generic (nullarySum, nullarySumWith)
 import Data.Generic.Rep (class Generic)
 import Data.Show.Generic (genericShow)
 import Effect (Effect)
 import Effect.Console (log)
 import Test.QuickCheck (quickCheck)
 import Test.QuickCheck.Arbitrary (genericArbitrary)
 import Test.QuickCheck.Gen (Gen)
+import Test.Sum (check)
 import Test.Util (propCodec)
 
 data MySum = Ctor1 | Ctor2 | MoarCtors
@@ -27,3 +28,9 @@ main ∷ Effect Unit
 main = do
   log "Check nullarySum"
   quickCheck (propCodec genMySum (nullarySum "MySum"))
+
+  let opts = { mapTag: \tag → "My" <> tag }
+
+  check (nullarySumWith opts "MySum") Ctor1 "\"MyCtor1\""
+  check (nullarySumWith opts "MySum") MoarCtors "\"MyMoarCtors\""
+