Generated reverse route method should have empty parentheses () depending on routes file

[gakuzzzz]

Play Version

2.8.2

API

Scala

Operating System

Not related to this problem

JDK

Not related to this problem

Library Dependencies

non

Expected Behavior

No warning in Scala2.13.3.

Actual Behavior

1. controller

package controllers

import javax.inject._
import play.api._
import play.api.mvc._

@Singleton
class HomeController @Inject()(val controllerComponents: ControllerComponents) extends BaseController {

  def index = Action { implicit request: Request[AnyContent] =>
    Ok("")
  }

  def redirect = Action { implicit request: Request[AnyContent] =>
    Redirect(routes.HomeController.index)
  }

}

2. compile

Warning is displayed.

[warn] D:\workspace\example\app\controllers\HomeController.scala:15:36: Auto-application to `()` is deprecated. Supply the empty argument list `()` explicitly to invoke method index,
[warn] or remove the empty argument list from its definition (Java-defined methods are exempt).
[warn] In Scala 3, an unapplied method like this will be eta-expanded into a function.
[warn]     Redirect(routes.HomeController.index)
[warn]                                    ^
[warn] one warning found

Related resources

• Deprecate auto-application of (non-Java-defined) methods with a single empty parameter list scala/scala#8833
• https://github.com/scala/scala/releases/tag/v2.13.3

[mkurz]

I think you just need to change

Redirect(routes.HomeController.index)

to

Redirect(routes.HomeController.index())

However I think we also need to fix Play's routes generator as well: #10364

[gakuzzzz]

Hi, @mkurz

Thanks, I think so too.

When the index was defined as def index() = Action{...}, we need to change to Redirect(routes.HomeController.index()).
However the index method has no side-effect. so it is defined as def index = Action{...}.
We expect that Play's routes generator generates no-parentheses method.

regards,

[mkurz]

Fix is here #10671