0.7.1: Circe-converted decoders handle nulls, better errors

Author: domaspoliakas

circe/src/main/scala/mongo4cats/circe.scala

@@ -50,10 +50,11 @@ object circe extends JsonCodecs {
 
     implicit def circeDecoderToDecoder[A: Decoder] = new BsonDecoder[A] {
       def apply(b: BsonValue) = {
-        val doc = BsonDocument(RootTag -> b).toJson()
+        val doc = BsonDocument(RootTag -> (if (b == null) new BsonNull else b)).toJson()
         val json = parser.parse(doc)
-        val decoder = Decoder.instance[A](_.get[A](RootTag))
-        json
+        val jsonWithoutRoot = json.flatMap(_.hcursor.get[Json](RootTag))
+        val decoder = Decoder.instance[A](_.as[A])
+        jsonWithoutRoot
           .flatMap(decoder.decodeJson(_))
           .leftMap(x =>
             BsonDecodeError {

circe/src/test/scala/mongo4cats/circe.scala

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2020 Kirill5k
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package mongo4cats
+
+import org.scalatest.wordspec.AnyWordSpec
+import org.scalatest.matchers.should.Matchers
+import org.bson.BsonString
+import io.circe.Decoder
+import org.scalatest.EitherValues
+import io.circe.DecodingFailure
+
+class CirceSpec extends AnyWordSpec with Matchers with EitherValues {
+
+  "circe conversions" should {
+    "decode null as if it was Json.null" in {
+      circe.implicits.circeDecoderToDecoder[Unit](Decoder.instance { c => 
+        c.value.asNull.toRight(DecodingFailure("wasn't null!", Nil))
+      }).apply(null) shouldBe Right(())
+    }
+
+    "not report the internal root tag in history when reporting errors" in {
+
+      val deco = Decoder.instance(h => {
+        h.get[String]("hek")(Decoder.failedWithMessage("Bad!"))
+      })
+
+      val res = circe.implicits.circeDecoderToDecoder[String](deco).apply(new BsonString("hek"))
+
+      res.left.value.msg shouldBe "An error occured during decoding BsonValue BsonString{value='hek'}: DecodingFailure(Attempt to decode value on failed cursor, List(DownField(hek)))"
+
+    }
+  }
+
+}

version.sbt

@@ -1 +1 @@
-version in ThisBuild := "0.7.0"
+version in ThisBuild := "0.7.1"