test.scala

case class GHUser(
                 login: String,
                 id: Long,
                 avatar_url: String,
                 gravatar_id: Option[String],
                 url: String,
                 html_url: String,
                 followers_url: String,
                 following_url: Option[String],
                 gists_url: Option[String],
                 starred_url: String,
                 subscriptions_url: String,
                 organizations_url: String,
                 repos_url: String,
                 events_url: Option[String],
                 received_events_url: String,
                 `type`: String,
                 site_admin: Boolean
                 )
case class GHPullRequestMini(project :String,
                             url: String,
                             title: String,
                             state: String,
                             user: GHUser,
                             body: String,
                             created_at: String,
                             updated_at: String,
                             closed_at: Option[String],
                             merged_at: Option[String],
                             assignee: Option[GHUser],
                             branch: String
                              )
implicit val GHUserJsonWrite = {
    import play.api.data.mapping.json.Writes._ // let's no leak implicits everywhere
    Write.gen[GHUser, JsObject]
  }
implicit val GHPullRequestMiniJsonWrite = {
    import play.api.data.mapping.json.Writes._ // let's no leak implicits everywhere
    Write.gen[GHPullRequestMini, JsObject]
  }
  
   val pullRequests:Seq[GHPullRequestMini] = ...
   val json = To[Seq[GHPullRequestMini], JsObject](pullRequests)
   // => could not find implicit value for parameter w: play.api.data.mapping.WriteLike[Seq[models.GHPullRequestMini],play.api.libs.json.JsObject]

Il faut utiliser JsValue:

scala> To[Seq[Int], JsArray](1 to 10)
<console>:17: error: could not find implicit value for parameter w: play.api.data.mapping.WriteLike[Seq[Int],play.api.libs.json.JsArray]
              To[Seq[Int], JsArray](1 to 10)

scala> To[Seq[Int], JsValue](1 to 10)
res3: play.api.libs.json.JsValue = [1,2,3,4,5,6,7,8,9,10]

JsValue c'est bon pour un type simple par pour une case class j'ai l'impression.

val json = To[Seq[GHPullRequestMini], JsValue](pullRequests) // => could not find implicit value for parameter w: play.api.data.mapping.WriteLike[Seq[models.GHPullRequestMini],play.api.libs.json.JsValue]

du coup il faut que je modifie mes Write comme cela
Write.gen[GHPullRequestMini, JsValue] => value ~ is not a member of play.api.data.mapping.Write[String,play.api.libs.json.JsValue] Note: implicit value GHPullRequestMiniJsonWrite is not applicable here because it comes after the application point and it lacks an explicit result type

Mouai en fait pour generer le Write il faut un JsObject car tu as besoin du Monoid sur ce type. Par contre pour la Seq i tu faut une JsValue du coup il faut que tu type explicitement GHPullRequestMiniJsonWrite

Exemple:

case class Foo(s: String, i: Int)
val foos = Seq(Foo("foo", 1))
implicit val ws: Write[Foo, JsValue] = Write.gen[Foo, JsObject]
scala> To[Seq[Foo], JsValue](foos)
res7: play.api.libs.json.JsValue = [{"s":"foo","i":1}]