Fix Decoder[None.type] (#1726)

circe · Apr 20, 2021 · c8e7733 · c8e7733
1 parent 1ae596b
commit c8e7733
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Showing 2 changed files with 30 additions and 4 deletions.
diff --git a/modules/core/shared/src/main/scala/io/circe/Decoder.scala b/modules/core/shared/src/main/scala/io/circe/Decoder.scala
@@ -910,11 +910,11 @@ object Decoder
     }
   }
 
-  private[this] final val rightNone: Either[DecodingFailure, Option[Nothing]] = Right(None)
-  private[this] final val validNone: ValidatedNel[DecodingFailure, Option[Nothing]] = Validated.valid(None)
+  private[this] final val rightNone: Either[DecodingFailure, None.type] = Right(None)
+  private[this] final val validNone: ValidatedNel[DecodingFailure, None.type] = Validated.valid(None)
 
-  private[circe] final val keyMissingNone: Decoder.Result[Option[Nothing]] = Right(None)
-  private[circe] final val keyMissingNoneAccumulating: AccumulatingResult[Option[Nothing]] =
+  private[circe] final val keyMissingNone: Decoder.Result[None.type] = Right(None)
+  private[circe] final val keyMissingNoneAccumulating: AccumulatingResult[None.type] =
     Validated.valid(None)
 
   /**
@@ -964,6 +964,22 @@ object Decoder
     else {
       Left(DecodingFailure("None", c.history))
     }
+    final override def tryDecode(c: ACursor): Decoder.Result[None.type] = c match {
+      case c: HCursor =>
+        if (c.value.isNull) rightNone
+        else Left(DecodingFailure("None", c.history))
+      case c: FailedCursor =>
+        if (!c.incorrectFocus) keyMissingNone else Left(DecodingFailure("None", c.history))
+    }
+
+    final override def tryDecodeAccumulating(c: ACursor): AccumulatingResult[None.type] = c match {
+      case c: HCursor =>
+        if (c.value.isNull) validNone
+        else Validated.invalidNel(DecodingFailure("None", c.history))
+      case c: FailedCursor =>
+        if (!c.incorrectFocus) keyMissingNoneAccumulating
+        else Validated.invalidNel(DecodingFailure("None", c.history))
+    }
   }
 
   /**

diff --git a/modules/tests/shared/src/test/scala/io/circe/CodecSuites.scala b/modules/tests/shared/src/test/scala/io/circe/CodecSuites.scala
@@ -157,6 +157,16 @@ class StdLibCodecSuite extends CirceMunitSuite with ArrayFactoryInstance {
 
     assert(result.isLeft)
   }
+
+  test("None.type decoder should succeed for missing fields") {
+    val n = Json.obj()
+    val decoder = Decoder[None.type].at("foo")
+
+    val result1 = decoder.decodeJson(n)
+    assert(result1.isRight)
+    val result2 = decoder.decodeAccumulating(HCursor.fromJson(n))
+    assert(result2.isValid)
+  }
 }
 
 class CatsCodecSuite extends CirceMunitSuite with StreamFactoryInstance {