Derivation is failing to resolve a custom ConfigConvert materializer

Context: I’m working on an integration of coulomb with pureconfig.

I have a generator (see this pull-req) for ConfigConvert that appears to work well in isolation (it will instantiate implicitly when using to and from on a coulomb Quantity). However, when I try to declare a configuration case class that has Quantity members, the corresponding reader will not resolve implicitly, unless I explicitly declare ConfigConvert, in which case it will work. Here’s an example session, where you can see my first loadConfig fail, and then after I declare the two ConfigConvert values explicitly, it succeeds:

scala> import coulomb._, coulomb.si._, coulomb.time._, coulomb.info._, coulomb.typesafeconfig._, coulomb.parser._, com.typesafe.config._, coulomb.siprefix._, shapeless._, org.apache.avro._, org.apache.avro.generic._, org.apache.avro.file._, coulomb.avro._, coulomb.binprefix._, _root_.pureconfig._, _root_.pureconfig.generic.auto._, coulomb.pureconfig._

scala> implicit val qp = QuantityParser[Second :: Byte :: Hour :: Giga :: HNil]
qp: coulomb.parser.QuantityParser = coulomb.parser.QuantityParser@67b5409b

scala> case class QC(t: Quantity[Double, Second], m: Quantity[Double, Mega %* Byte])
defined class QC

scala> val conf = ConfigFactory.parseString("""{ "t": { "value": 1, "unit":"hour" }, "m": { "value": 1, "unit": "gigabyte" } }""") 
conf: com.typesafe.config.Config = Config(SimpleConfigObject({"m":{"unit":"gigabyte","value":1},"t":{"unit":"hour","value":1}}))

scala> val conf = ConfigFactory.parseString("""{ t: { value: 1, unit: "hour" }, m: { value: 1, unit: "gigabyte" } }""") 
conf: com.typesafe.config.Config = Config(SimpleConfigObject({"m":{"unit":"gigabyte","value":1},"t":{"unit":"hour","value":1}}))

scala> loadConfig[QC](conf)
                     ^
       error: Cannot find an implicit instance of pureconfig.ConfigReader[QC].
       If you are trying to read or write a case class or sealed trait consider using PureConfig's auto derivation by adding `import pureconfig.generic.auto._`

scala> implicit val ttt = implicitly[ConfigConvert[Quantity[Double, Second]]]
ttt: pureconfig.ConfigConvert[coulomb.Quantity[Double,coulomb.si.Second]] = coulomb.pureconfig.package$$anon$1@71f0008b

scala> implicit val ttt2 = implicitly[ConfigConvert[Quantity[Double, Mega %* Byte]]]
ttt2: pureconfig.ConfigConvert[coulomb.Quantity[Double,coulomb.siprefix.Mega %* coulomb.info.Byte]] = coulomb.pureconfig.package$$anon$1@721a582

scala> loadConfig[QC](conf)
res1: pureconfig.ConfigReader.Result[QC] = Right(QC(Quantity(3600.0),Quantity(1000.0)))

[erikerlandson]

@ruippeixotog thanks! For fun, I tried compiling it as part of the test build. I dropped the following into my source:

object pctest {
  import coulomb._, coulomb.si._, coulomb.time._, coulomb.info._, coulomb.typesafeconfig._, coulomb.parser._, com.typesafe.config._, coulomb.siprefix._, shapeless._, coulomb.binprefix._, _root_.pureconfig._, _root_.pureconfig.generic.auto._, coulomb.pureconfig._

  implicit val qp = QuantityParser[Second :: Byte :: Hour :: Giga :: HNil]

  case class QC(t: Quantity[Double, Second], m: Quantity[Double, Mega %* Byte])

  val conf = ConfigFactory.parseString("""{ "t": { "value": 1, "unit":"hour" }, "m": { "value": 1, "unit": "gigabyte" } }""") 

  val qc = loadConfig[QC](conf)  // Now I compile!
}

When I do it that way, it compiles fine! That suggests it isn’t a bug in pureconfig, but maybe the REPL’s environment is not set up quite right to make the implicit tree resolve.

[ruippeixotog]

That’s great to hear! The Scala REPL is indeed very flaky, I’m glad it works in a normal environment.