Add a TwirlModule to compile Twirl templates (#271)

* initial implementation

* Upgrade to the latest version

* Add tests
* Update the code to comply with the new API
* Use reflection to call TwirlCompiler.compile function

* Run twirllib.test on CI

* Use the Java API as a workaround

* wip

* Cleanup the code (code review)

* Add an example to call the Scala API

* twirl that works with scala API

* Create functions to override the default settings (will be available in the future)

8 files changed, 265 insertions, 3 deletions

diff --git a/build.sc b/build.sc
index 86ef2d00..ac6c2ea9 100755
--- a/build.sc
+++ b/build.sc
@@ -196,6 +196,12 @@ object scalajslib extends MillModule {
   }
 }
 
+object twirllib extends MillModule {
+
+  def moduleDeps = Seq(scalalib)
+
+}
+
 def testRepos = T{
   Seq(
     "MILL_ACYCLIC_REPO" ->
diff --git a/ci/test-mill-0.sh b/ci/test-mill-0.sh
index daae5bd6..e63760cf 100755
--- a/ci/test-mill-0.sh
+++ b/ci/test-mill-0.sh
@@ -6,4 +6,4 @@ set -eux
 git clean -xdf
 
 # Run tests
-mill -i all {main,scalalib,scalajslib,main.client}.test
+mill -i all {main,scalalib,scalajslib,twirllib,main.client}.test
diff --git a/ci/test-mill-dev.sh b/ci/test-mill-dev.sh
index 459f3eb1..f5a8bfcd 100755
--- a/ci/test-mill-dev.sh
+++ b/ci/test-mill-dev.sh
@@ -11,5 +11,5 @@ mill -i dev.assembly
 rm -rf ~/.mill
 
 # Second build & run tests
-out/dev/assembly/dest/mill -i all {main,scalalib,scalajslib}.test
+out/dev/assembly/dest/mill -i all {main,scalalib,scalajslib,twirllib}.test
 
diff --git a/main/test/src/mill/define/CacherTests.scala b/main/test/src/mill/define/CacherTests.scala
index 03232930..98f2b7f8 100644
--- a/main/test/src/mill/define/CacherTests.scala
+++ b/main/test/src/mill/define/CacherTests.scala
@@ -17,7 +17,7 @@ object CacherTests extends TestSuite{
   }
   object Middle extends Middle
   trait Middle extends Base{
-    def value = T{ super.value() + 2}
+    override def value = T{ super.value() + 2}
     def overriden = T{ super.value()}
   }
   object Terminal extends  Terminal
diff --git a/twirllib/src/mill/twirllib/TwirlModule.scala b/twirllib/src/mill/twirllib/TwirlModule.scala
new file mode 100644
index 00000000..2df70a1f
--- /dev/null
+++ b/twirllib/src/mill/twirllib/TwirlModule.scala
@@ -0,0 +1,56 @@
+package mill
+package twirllib
+
+import coursier.{Cache, MavenRepository}
+import mill.define.Sources
+import mill.eval.PathRef
+import mill.scalalib.Lib.resolveDependencies
+import mill.scalalib._
+import mill.util.Loose
+
+import scala.io.Codec
+import scala.util.Properties
+
+trait TwirlModule extends mill.Module {
+
+  def twirlVersion: T[String]
+
+  def twirlSources: Sources = T.sources {
+    millSourcePath / 'views
+  }
+
+  def twirlClasspath: T[Loose.Agg[PathRef]] = T {
+    resolveDependencies(
+      Seq(
+        Cache.ivy2Local,
+        MavenRepository("https://repo1.maven.org/maven2")
+      ),
+      Lib.depToDependency(_, "2.12.4"),
+      Seq(
+        ivy"com.typesafe.play::twirl-compiler:${twirlVersion()}",
+        ivy"org.scala-lang.modules::scala-parser-combinators:1.1.0"
+      )
+    )
+  }
+
+  // REMIND currently it's not possible to override these default settings
+  private def twirlAdditionalImports: Seq[String] = Nil
+
+  private def twirlConstructorAnnotations: Seq[String] = Nil
+
+  private def twirlCodec: Codec = Codec(Properties.sourceEncoding)
+
+  private def twirlInclusiveDot: Boolean = false
+
+  def compileTwirl: T[CompilationResult] = T.persistent {
+    TwirlWorkerApi.twirlWorker
+      .compile(
+        twirlClasspath().map(_.path),
+        twirlSources().map(_.path),
+        T.ctx().dest,
+        twirlAdditionalImports,
+        twirlConstructorAnnotations,
+        twirlCodec,
+        twirlInclusiveDot)
+  }
+}
diff --git a/twirllib/src/mill/twirllib/TwirlWorker.scala b/twirllib/src/mill/twirllib/TwirlWorker.scala
new file mode 100644
index 00000000..f351ff2f
--- /dev/null
+++ b/twirllib/src/mill/twirllib/TwirlWorker.scala
@@ -0,0 +1,119 @@
+package mill
+package twirllib
+
+import java.io.File
+import java.lang.reflect.Method
+import java.net.URLClassLoader
+
+import ammonite.ops.{Path, ls}
+import mill.eval.PathRef
+import mill.scalalib.CompilationResult
+
+import scala.io.Codec
+
+class TwirlWorker {
+
+  private var twirlInstanceCache = Option.empty[(Long, TwirlWorkerApi)]
+
+  private def twirl(twirlClasspath: Agg[Path]) = {
+    val classloaderSig = twirlClasspath.map(p => p.toString().hashCode + p.mtime.toMillis).sum
+    twirlInstanceCache match {
+      case Some((sig, instance)) if sig == classloaderSig => instance
+      case _ =>
+        val cl = new URLClassLoader(twirlClasspath.map(_.toIO.toURI.toURL).toArray)
+        val twirlCompilerClass = cl.loadClass("play.twirl.compiler.TwirlCompiler")
+        val compileMethod = twirlCompilerClass.getMethod("compile",
+          classOf[java.io.File],
+          classOf[java.io.File],
+          classOf[java.io.File],
+          classOf[java.lang.String],
+          cl.loadClass("scala.collection.Seq"),
+          cl.loadClass("scala.collection.Seq"),
+          cl.loadClass("scala.io.Codec"),
+          classOf[Boolean])
+
+        val defaultAdditionalImportsMethod = twirlCompilerClass.getMethod("compile$default$5")
+        val defaultConstructorAnnotationsMethod = twirlCompilerClass.getMethod("compile$default$6")
+        val defaultCodecMethod = twirlCompilerClass.getMethod("compile$default$7")
+        val defaultFlagMethod = twirlCompilerClass.getMethod("compile$default$8")
+
+        val instance = new TwirlWorkerApi {
+          override def compileTwirl(source: File,
+                                    sourceDirectory: File,
+                                    generatedDirectory: File,
+                                    formatterType: String,
+                                    additionalImports: Seq[String],
+                                    constructorAnnotations: Seq[String],
+                                    codec: Codec,
+                                    inclusiveDot: Boolean) {
+            val o = compileMethod.invoke(null, source,
+              sourceDirectory,
+              generatedDirectory,
+              formatterType,
+              defaultAdditionalImportsMethod.invoke(null),
+              defaultConstructorAnnotationsMethod.invoke(null),
+              defaultCodecMethod.invoke(null),
+              defaultFlagMethod.invoke(null))
+          }
+        }
+        twirlInstanceCache = Some((classloaderSig, instance))
+        instance
+    }
+  }
+
+  def compile(twirlClasspath: Agg[Path],
+              sourceDirectories: Seq[Path],
+              dest: Path,
+              additionalImports: Seq[String],
+              constructorAnnotations: Seq[String],
+              codec: Codec,
+              inclusiveDot: Boolean)
+             (implicit ctx: mill.util.Ctx): mill.eval.Result[CompilationResult] = {
+    val compiler = twirl(twirlClasspath)
+
+    def compileTwirlDir(inputDir: Path) {
+      ls.rec(inputDir).filter(_.name.matches(".*.scala.(html|xml|js|txt)"))
+        .foreach { template =>
+          val extFormat = twirlExtensionFormat(template.name)
+          compiler.compileTwirl(template.toIO,
+            inputDir.toIO,
+            dest.toIO,
+            s"play.twirl.api.$extFormat",
+            additionalImports,
+            constructorAnnotations,
+            codec,
+            inclusiveDot
+          )
+        }
+    }
+
+    sourceDirectories.foreach(compileTwirlDir)
+
+    val zincFile = ctx.dest / 'zinc
+    val classesDir = ctx.dest / 'html
+
+    mill.eval.Result.Success(CompilationResult(zincFile, PathRef(classesDir)))
+  }
+
+  private def twirlExtensionFormat(name: String) =
+    if (name.endsWith("html")) "HtmlFormat"
+    else if (name.endsWith("xml")) "XmlFormat"
+    else if (name.endsWith("js")) "JavaScriptFormat"
+    else "TxtFormat"
+}
+
+trait TwirlWorkerApi {
+  def compileTwirl(source: File,
+                   sourceDirectory: File,
+                   generatedDirectory: File,
+                   formatterType: String,
+                   additionalImports: Seq[String],
+                   constructorAnnotations: Seq[String],
+                   codec: Codec,
+                   inclusiveDot: Boolean)
+}
+
+object TwirlWorkerApi {
+
+  def twirlWorker = new TwirlWorker()
+}
diff --git a/twirllib/test/resources/hello-world/core/views/hello.scala.html b/twirllib/test/resources/hello-world/core/views/hello.scala.html
new file mode 100644
index 00000000..acadf615
--- /dev/null
+++ b/twirllib/test/resources/hello-world/core/views/hello.scala.html
@@ -0,0 +1,6 @@
+@(title: String)
+<html>
+    <body>
+        <h1>@title</h1>
+    </body>
+</html>
\ No newline at end of file
diff --git a/twirllib/test/src/mill/twirllib/HelloWorldTests.scala b/twirllib/test/src/mill/twirllib/HelloWorldTests.scala
new file mode 100644
index 00000000..31928335
--- /dev/null
+++ b/twirllib/test/src/mill/twirllib/HelloWorldTests.scala
@@ -0,0 +1,75 @@
+package mill.twirllib
+
+import ammonite.ops.{Path, cp, ls, mkdir, pwd, rm, _}
+import mill.util.{TestEvaluator, TestUtil}
+import utest.framework.TestPath
+import utest.{TestSuite, Tests, assert, _}
+
+object HelloWorldTests extends TestSuite {
+
+  trait HelloBase extends TestUtil.BaseModule {
+    override def millSourcePath: Path = TestUtil.getSrcPathBase() / millOuterCtx.enclosing.split('.')
+  }
+
+  trait HelloWorldModule extends mill.twirllib.TwirlModule {
+    def twirlVersion = "1.0.0"
+  }
+
+  object HelloWorld extends HelloBase {
+
+    object core extends HelloWorldModule {
+      override def twirlVersion = "1.3.15"
+    }
+  }
+
+  val resourcePath: Path = pwd / 'twirllib / 'test / 'resources / "hello-world"
+
+  def workspaceTest[T, M <: TestUtil.BaseModule](m: M, resourcePath: Path = resourcePath)
+                                                (t: TestEvaluator[M] => T)
+                                                (implicit tp: TestPath): T = {
+    val eval = new TestEvaluator(m)
+    rm(m.millSourcePath)
+    rm(eval.outPath)
+    mkdir(m.millSourcePath / up)
+    cp(resourcePath, m.millSourcePath)
+    t(eval)
+  }
+
+  def compileClassfiles: Seq[RelPath] = Seq[RelPath](
+    "hello.template.scala"
+  )
+
+  def tests: Tests = Tests {
+    'twirlVersion - {
+
+      'fromBuild - workspaceTest(HelloWorld) { eval =>
+        val Right((result, evalCount)) = eval.apply(HelloWorld.core.twirlVersion)
+
+        assert(
+          result == "1.3.15",
+          evalCount > 0
+        )
+      }
+    }
+    'compileTwirl - workspaceTest(HelloWorld) { eval =>
+      val Right((result, evalCount)) = eval.apply(HelloWorld.core.compileTwirl)
+
+      val outputFiles = ls.rec(result.classes.path)
+      val expectedClassfiles = compileClassfiles.map(
+        eval.outPath / 'core / 'compileTwirl / 'dest / 'html / _
+      )
+      assert(
+        result.classes.path == eval.outPath / 'core / 'compileTwirl / 'dest / 'html,
+        outputFiles.nonEmpty,
+        outputFiles.forall(expectedClassfiles.contains),
+        outputFiles.size == 1,
+        evalCount > 0
+      )
+
+      // don't recompile if nothing changed
+      val Right((_, unchangedEvalCount)) = eval.apply(HelloWorld.core.compileTwirl)
+
+      assert(unchangedEvalCount == 0)
+    }
+  }
+}