Useless compile error while lacking encoder/decoder about circe

[djx314]

+1 to use implicitNotFound !
To decode and encode date, juest implicit

  implicit val dateTimeEncoder: Encoder[DateTime] = Encoder.instance(a => a.getMillis.asJson)
  implicit val dateTimeDecoder: Decoder[DateTime] = Decoder.instance(a => a.as[Long].map(new DateTime(_)))

Because of date has many format, I suggest that defined it in the documention and don't add a default format in the jfc.

[travisbrown]

Yeah, that's a pretty terrible error message—thanks for pointing it out.

The implementation of the generic derivation mechanism will be changing with #30, which I'm hoping to get done tomorrow, so after that dust settles I'll revisit this and #34, since things might be a little different by then. We should be able to use @implicitNotFound in a few places to improve these messages a lot (see for example this message in Finch).

[travisbrown]

I'm going to go ahead and close this since the following is a huge improvement:

<console>:59: error: could not find implicit value for parameter e: io.circe.Encoder[Foo]
           println(f.asJson.noSpaces)
                     ^

I'm not actually sure there's much additional useful information we could add with @implicitNotFound in this case, apart from maybe a pointer to the docs.