Play Framework

This module adds basic Play Framework support to mill:

  • configures mill for Play default directory layout,

  • integrates the Play routes compiler,

  • provides helpers for commonly used framework libraries,

  • optionally: integrates the Twirl template engine,

  • optionally: configures mill for single module play applications.

There is no specific Play Java support, building a Play Java application will require a bit of customization (mostly adding the proper dependencies).

Using the plugin

There are 2 base modules and 2 helper traits in this plugin, all of which can be found in mill.playlib.

The base modules:

  • PlayModule applies the default Play configuration (layout, dependencies, routes compilation, Twirl compilation and Akka HTTP server)

  • PlayApiModule applies the default Play configuration without Twirl templating. This is useful if your Play app is a pure API server or if you want to use a different templating engine.

The helper trait:

Using PlayModule

In order to use the PlayModule for your application, you need to provide the scala, Play and Twirl versions. You also need to define your own test object which extends the provided PlayTests trait.

build.mill
package build
import mill._
import $ivy.`com.lihaoyi::mill-contrib-playlib:`,  mill.playlib._

object core extends PlayModule {
    // config
    override def scalaVersion = Task { "2.13.12" }
    override def playVersion = Task { "2.8.20" }

    object test extends PlayTests
}

Using the above definition, your build will be configured to use the default Play layout:

.
├── build.mill
└── core
    ├── app
    │   ├── controllers
    │   └── views
    ├── conf
    │   └── application.conf
    │   └── routes
    │   └── ...
    ├── logs
    ├── public
    │   ├── images
    │   ├── javascripts
    │   └── stylesheets
    └── test
        └── controllers

The following compile dependencies will automatically be added to your build:

Agg(
  ivy"com.typesafe.play::play:${playVersion()}",
  ivy"com.typesafe.play::play-guice:${playVersion()}",
  ivy"com.typesafe.play::play-server:${playVersion()}",
  ivy"com.typesafe.play::play-logback:${playVersion()}"
)

Scala test will be setup as the default test framework and the following test dependencies will be added (the actual version depends on the version of Play you are pulling 2.6.x or 2.7.x):

ivy"org.scalatestplus.play::scalatestplus-play::5.1.0"

In order to have a working start command the following runtime dependency is also added:

ivy"com.typesafe.play::play-akka-http-server:${playVersion()}"

or

ivy"com.typesafe.play::play-pekko-http-server:${playVersion()}"

depending on the play version

Using PlayApiModule

The PlayApiModule trait behaves the same as the PlayModule trait but it won’t process .scala .html files:

build.mill
package build
import mill._
import $ivy.`com.lihaoyi::mill-contrib-playlib:`,  mill.playlib._

object core extends PlayApiModule {
    // config
    override def scalaVersion = Task { "2.13.12" }
    override def playVersion = Task { "2.8.20" }

    object test extends PlayTests
}

Play configuration options

The Play modules themselves don’t have specific configuration options at this point but the router module configuration options and the contrib/twirllib.adoc#_twirl_configuration_options are applicable.

Additional play libraries

The following helpers are available to provide additional Play Framework dependencies:

  • core() - added by default ,

  • guice() - added by default,

  • server() - added by default,

  • logback() - added by default,

  • evolutions() - optional,

  • jdbc() - optional,

  • filters() - optional,

  • ws() - optional,

  • caffeine() - optional.

If you want to add an optional library using the helper you can do so by overriding ivyDeps like in the following example build:

build.mill
package build
import mill._
import $ivy.`com.lihaoyi::mill-contrib-playlib:$MILL_VERSION`, mill.playlib._

object core extends PlayApiModule {
    // config
    override def scalaVersion = Task { "2.13.12" }
    override def playVersion = Task { "2.8.20" }

    object test extends PlayTests

    override def ivyDeps = Task { super.ivyDeps() ++ Agg(ws(), filters()) }
}

Commands equivalence

Mill commands are tasks on a named build. For example if your build is called core:

  • compile: core.compile

  • run: NOT Implemented yet. It can be approximated with mill -w core.runBackground but this starts a server in PROD mode which:

  • doesn’t do any kind of classloading magic (meaning potentially slower restarts)

  • returns less detailed error messages (no source code extract and line numbers)

  • can sometimes fail because of a leftover RUNNING_PID file

  • start: core.start or core.run both start the server in PROD mode.

  • test: core.test

  • dist: NOT Implemented yet. However you can use the equivalent core.assembly command to get a runnable fat jar of the project. The packaging is slightly different but should be find for a production deployment.

Using RootModule

The RootModule abstract class allows you to have the build descriptor at the same level as the source code on the filesystem. You can move from there to a multi-module build either by refactoring your directory layout into multiple subdirectories or by using mill’s nested modules feature.

Looking back at the sample build definition in Using PlayModule:

build.mill
package build
import mill._
import $ivy.`com.lihaoyi::mill-contrib-playlib:`, mill.playlib._

object core extends PlayModule {
    // config
    override def scalaVersion = Task { "2.13.12" }
    override def playVersion = Task { "2.8.20" }

    object test extends PlayTests
}

The directory layout was:

.
├── build.mill
└── core
    ├── app
    │   ├── controllers
    │   └── views
    ├── conf
    │   └── application.conf
    │   └── routes
    │   └── ...
    ├── logs
    ├── public
    │   ├── images
    │   ├── javascripts
    │   └── stylesheets
    └── test
        └── controllers

by extending RootModule in your build:

build.mill
package build
import mill._
import $ivy.`com.lihaoyi::mill-contrib-playlib:`,  mill.playlib._

object build extends RootModule with PlayModule {
 // config
 override def scalaVersion = Task { "2.13.12" }
 override def playVersion = Task { "2.8.20" }

 object test extends PlayTests
}

the layout becomes:

.
├── build.mill
├── app
│   ├── controllers
│   └── views
├── conf
│   └── application.conf
│   └── routes
│   └── ...
├── logs
├── public
│   ├── images
│   ├── javascripts
│   └── stylesheets
└── test
    └── controllers

Using the router module directly

If you want to use the router module in a project which doesn’t use the default Play layout, you can mix-in the mill.playlib.routesModule trait directly when defining your module. Your app must define playVersion and scalaVersion.

build.mill
package build
import mill._
import $ivy.`com.lihaoyi::mill-contrib-playlib:`,  mill.playlib._

object app extends ScalaModule with RouterModule {
  def playVersion = Task { "2.8.20" }
  def scalaVersion = Task { "2.13.12" }
}

Router Configuration options

  • def playVersion: T[String] (mandatory) - The version of Play to use to compile the routes file.

  • def scalaVersion: T[String] - The scalaVersion in use in your project.

  • def routes: Sources - The directory which contains your route files. (Defaults to : routes/)

  • def routesAdditionalImport: Seq[String] - Additional imports to use in the generated routers. (Defaults to Seq("controllers.Assets.Asset", "play.libs.F")

  • def generateForwardsRouter: Boolean = true - Enables the forward router generation.

  • def generateReverseRouter: Boolean = true - Enables the reverse router generation.

  • def namespaceReverseRouter: Boolean = false - Enables the namespacing of reverse routers.

  • def generatorType: RouteCompilerType = RouteCompilerType.InjectedGenerator - The routes compiler type, one of RouteCompilerType.InjectedGenerator or RouteCompilerType.StaticGenerator

Details

The following filesystem layout is expected by default:

.
├── app
│   └── routes
│       └── routes
└── build.mill

RouterModule adds the compileRouter task to the module:

$ mill app.compileRouter

(it will be automatically run whenever you compile your module)

This task will compile routes templates into the out/app/compileRouter/dest directory. This directory must be added to the generated sources of the module to be compiled and made accessible from the rest of the code. This is done by default in the trait, but if you need to have a custom override for generatedSources you can get the list of files from routerClasses

To add additional imports to all of the routes:

build.mill
package build
import mill.scalalib._

import $ivy.`com.lihaoyi::mill-contrib-playlib:$MILL_VERSION`,  mill.playlib._

object app extends ScalaModule with RouterModule {
  def playVersion = "2.8.20"
  override def routesAdditionalImport = Seq("my.additional.stuff._", "my.other.stuff._")
}