JsPath.prune should not repath on success

Play JSON Version (2.5.x / etc)

2.6.9

API (Scala / Java / Neither / Both)

Scala

Operating System (Ubuntu 15.10 / MacOS 10.10 / Windows 10)

macOS 10.13.6

JDK (Oracle 1.8.0_72, OpenJDK 1.8.x, Azul Zing)

java version "1.8.0_172"
Java(TM) SE Runtime Environment (build 1.8.0_172-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.172-b11, mixed mode)

Library Dependencies

N/A

Expected Behavior

scala> :paste
// Entering paste mode (ctrl-D to finish)

import play.api.libs.json._

val js = Json.parse("""{
                       |  "a": 1,
                       |  "b": 2,
                       |  "c": 3
                       |}""".stripMargin)
val removeAAndB = (__ \ 'a).json.prune andThen (__ \ 'b).json.prune
val removeAAndBPickD = removeAAndB andThen (__ \ 'd).json.pick

// Exiting paste mode, now interpreting.

import play.api.libs.json._
js: play.api.libs.json.JsValue = {"a":1,"b":2,"c":3}
removeAAndB: play.api.libs.json.Reads[play.api.libs.json.JsObject] = play.api.libs.json.Reads$$anon$8@29d080fc
removeAAndBPickD: play.api.libs.json.Reads[play.api.libs.json.JsValue] = play.api.libs.json.Reads$$anon$8@1ed855bd

scala> removeAAndB.reads(js)
res0: play.api.libs.json.JsResult[play.api.libs.json.JsObject] = JsSuccess({"c":3},/a/b)

scala> removeAAndBPickD.reads(js)
res1: play.api.libs.json.JsResult[play.api.libs.json.JsValue] = JsError(List((/a/b/d,List(JsonValidationError(List(error.path.missing),WrappedArray())))))

Should evaluate to:

JsError(List((/d,List(JsonValidationError(List(error.path.missing),WrappedArray())))))

Actual Behavior

It evaluates to:

JsError(List((/a/b/d,List(JsonValidationError(List(error.path.missing),WrappedArray())))))

The issue is that prune is effectively repathing the result and so it does not compose properly with subsequent Reads. It makes sense to use the path in the error cases but not success.

Reproducible Test Case

See above.

Start at the JsPath.prune implementation and reproduce the composed Reads behavior shown in the issue. Add a regression test for pruning a and b before picking a missing d, confirming the error path is /d while prune errors retain their own paths; run the relevant Play JSON tests.