Attaching HandlerAspect to a Routes object with mulitple dependencies does not work (using Scala2)

[kurgansoft]

The operator '@@' is used to attach a HandlerAspect to a Routes object.

It is working fine if applying results in a Routes object with no dependencies.

If the result is a Routes object with one dependency, it still works, but that dependency needs to be declared explicitly, like:
.@@[Int]

However if the result is a Routes object with multiple dependencies, it won't work even if we declare those dependencies explicitly.

Using scala 3 everything works as expected, and the type does not need to be declared explicitly either.

Example code to reproduce the issue:

//> using dep dev.zio::zio-http::3.0.0-RC10
//> using scala 2.13.14

import zio.http.codec.{HttpCodec, StatusCodec}
import zio.http.endpoint.{AuthType, Endpoint}
import zio.http.{HandlerAspect, Header, Route, RoutePattern, Routes, withContext}
import zio._

object Issue extends App {
  val effectWithNoDependency: IO[Nothing, String] = for {
    _ <- ZIO.log("executing effect with no dependency")
  } yield "hardcodedResult - effectWithNoDependency"

  val effectWithOneDependency: ZIO[Int, Nothing, String] = for {
    magicNumber <- ZIO.service[Int]
    _ <- ZIO.log(s"executing effect with one dependency; magic number is $magicNumber")
  } yield "hardcodedResult - effectWithOneDependency"

  val effectWithTwoDependency: ZIO[Int & Long, Nothing, String] = for {
    magicNumber <- ZIO.service[Int]
    magicNumber2 <- ZIO.service[Long]
    _ <- ZIO.log(s"executing effect with two dependency; magic numbers are: $magicNumber and $magicNumber2")
  } yield "hardcodedResult - effectWithTwoDependency"

  val authContext: HandlerAspect[Any, String] = HandlerAspect.customAuthProviding[String] { request =>
    {
      request.headers.get(Header.Authorization).flatMap {
        case Header.Authorization.Basic(uname, secret) if uname.reverse == secret.value.mkString =>
          Some(uname)
        case _ =>
          None
      }
    }
  }

  val endpoint = Endpoint(RoutePattern.GET / "route1")
    .outCodec[String](StatusCodec.Ok ++ HttpCodec.content[String])
    .auth(AuthType.Basic)

  val route1: Route[String, Nothing] = endpoint.implement((_: Unit) =>
    withContext((username: String) => ZIO.log(s"username is $username")) *>
      effectWithNoDependency
  )

  // The authContext eliminates the String dependency
  val routes1: Routes[Any, Nothing] = Routes(route1) @@ authContext

  val route2: Route[Int & String, Nothing] = endpoint.implement((_: Unit) =>
    withContext((username: String) => ZIO.log(s"username is $username")) *>
      effectWithOneDependency
  )

  // The authContext eliminates the String dependency, so only the Int dependency remains
  // But what remains - it has to be declared explicitly
  val routes2: Routes[Int, Nothing] = Routes(route2).@@[Int](authContext)

  val route3: Route[Int & Long & String, Nothing] = endpoint.implement((_: Unit) =>
    withContext((username: String) => ZIO.log(s"username is $username")) *>
      effectWithTwoDependency
  )

  // Like in routes2 we would like to eliminate the String dependency so only Int and Long would remain.
  // However, the below gives this compilation error:
  // "A Tag may not contain an intersection type, yet have provided: Int with Long"
  val routes3: Routes[Int & Long, Nothing] = Routes(route3).@@[Int & Long](authContext)
}

[jdegoes]

/bounty $150 for fix and test

[algora-pbc]

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Attempt	Started (GMT+0)	Solution
🟢 @stdthoth	Sep 10, 2024, 3:38:30 PM	WIP
🟢 @asr2003	Sep 11, 2024, 6:11:34 AM	WIP
🟢 @pawelsadlo		#3128

[stdthoth]

/attempt #3112

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[asr2003]

/attempt #3112

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[frekw]

I'm still running into this with zio-http 3.0.1, needing to resort to the previous workaround:

type Env = UploadService with AuthInterceptor

val withViewer = Middleware.customAuthProvidingZIO[AuthInterceptor, Viewer](req =>
  (for {
    interceptor <- ZIO.service[AuthInterceptor]
    viewer <- interceptor.intercept(req)
  } yield Some(viewer))

val routes = API.upload.@@[Env](withViewer)

or otherwise it fails with:

Cannot prove that Env0 with Viewer <:< Viewer with UploadService with Viewer