add a codec annotation to mark a sealed trait as having all case object members

[googley42]

in zio-dynamodb (which is uses zio-schema) we have the @enumOfCaseObjects trait level annotation to signify that all members as case objects. This gets read by our codec generation code to produce a more compact encoding that is used in many legacy databases.

eg given this model:

sealed trait TrafficLight
case object GREEN extends TrafficLight 
case object RED extends TrafficLight
final case class Box(trafficLightColour: TrafficLight)

The default tagged union encoding is something like:

Map(trafficLightColour -> Map(String(GREEN) -> Null))

after you add the annotation to the sealed trait, the encoding is more compact, with one less level of indirection:

Map(trafficLightColour -> String(GREEN))

This issue is related to this one Define a canonical set of annotations that can be applied to sealed traits, case classes, and fields

[jdegoes]

Maybe @SimpleEnum to indicate all terms are case objects.

[jdegoes]

/bounty $75

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Attempt	Started (GMT+0)	Solution
🟢 @pablf	May 23, 2023, 12:34:35 PM	#564

[andrzejressel]

Weird, when working with JSON parser recently I swore I've seen code like that - if everything is sealed trait is CaseObject0 it deserialises as single string. I'll take a look later.

[pablf]

/attempt #506

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