Typed Twirl

Twirl is the Play template engine. See the Play documentation for the template engine for more information about the template syntax.

Typed Twirl is a variant that limits the types of values that can be rendered in a template to only those for which there exists an instance of the FormatValue typeclass.

The motivation is to eliminate the chance of accidentally rendering a value using it's toString representation. For example, using cats.data.NonEmptyList, it's easy to forget to call .toList and end up with this:

<ul>
  @NonEmptyList.of(1, 2, 3).map { i => <li>@i</li> }
</ul>

// what you intended to render
<ul><li>1</li><li>2</li><li>3</li></ul>
// what you actually get
<ul>NonEmptyList(&lt;li&gt;1&lt;/li&gt;, &lt;li&gt;2&lt;/li&gt;, &lt;li&gt;3&lt;/li&gt;)</ul>

sbt-typed-twirl

Twirl can also be used outside of Play. An sbt plugin is provided for easy integration with Scala or Java projects.

sbt-typed-twirl requires sbt 1.3.0 or higher.

To add the sbt plugin to your project add the sbt plugin dependency in project/plugins.sbt:

resolvers += "bondlink-maven-repo" at "https://maven.bondlink-cdn.com"
addSbtPlugin("bondlink" % "sbt-typed-twirl" % "0.3.2")

someProject.enablePlugins(SbtTwirl)

If you only have a single project and are using a build.sbt file, create a root project and enable the twirl plugin like this:

lazy val root = (project in file(".")).enablePlugins(SbtTwirl)

Template files

Twirl template files are expected to be placed under src/main/twirl or src/test/twirl, similar to scala or java sources. The source locations for template files can be configured.

Template files must be named {name}.scala.{ext} where ext can be html, js, xml, or txt.

The Twirl template compiler is automatically added as a source generator for both the main/compile and test configurations. When you run compile or Test/compile the Twirl compiler will generate Scala source files from the templates and then these Scala sources will be compiled along with the rest of your project.

Additional imports

To add additional imports for the Scala code in template files, use the templateImports key. For example:

TwirlKeys.templateImports += "org.example._"

Source directories

To configure the source directories where template files will be found, use the compileTemplates / sourceDirectories key. For example, to have template sources alongside Scala or Java source files:

Compile / TwirlKeys.compileTemplates / sourceDirectories := (Compile / unmanagedSourceDirectories).value

Credits

The name twirl was thought up by the Spray team and refers to the magic @ character in the template language, which is sometimes called "twirl".

The first stand-alone version of Twirl was created by the Spray team.

An optimized version of the Twirl parser was contributed by the Scala IDE team.