Cross-build to Scala 3

.scala-steward.conf

@@ -5,15 +5,6 @@ updates.pin  = [
   // https://github.com/akka/akka/blob/master/project/Dependencies.scala#L24
   { groupId = "com.fasterxml.jackson.core", version = "2.10." }
   { groupId = "com.fasterxml.jackson.datatype", version = "2.10." }
-  // "It is not forward binary compatible with 1.0.x: libraries compiled with 1.1.0 cannot be used with 1.0.x."
-  // https://users.scala-lang.org/t/announcing-scala-js-1-1-0/6053/3?u=sjrd
-  { groupId = "org.scala-js", artifactId = "sbt-scalajs", version = "1.0." }
-  { groupId = "org.scala-js", artifactId = "scalajs-compiler", version = "1.0." }
-  { groupId = "org.scala-js", artifactId = "scalajs-library", version = "1.0." }
-  { groupId = "org.scala-js", artifactId = "scalajs-test-bridge", version = "1.0." }
-  // Scalatest 3.2.x pulls in ScalaJs 1.1
-  { groupId = "org.scalatest", artifactId = "scalatest", version = "3.1." }
-  { groupId = "org.scalatestplus", artifactId = "scalacheck-1-14", version = "3.1." }
 ]
 
 commits.message = "${artifactName} ${nextVersion} (was ${currentVersion})"

.scalafmt.conf

@@ -3,7 +3,8 @@ assumeStandardLibraryStripMargin = true
 danglingParentheses = true
 docstrings = JavaDoc
 maxColumn = 120
-project.excludeFilters += core/play/src/main/scala/play/core/hidden/ObjectMappings.scala
+#scalafmt does not support Scala 3 syntax yet (`inline`)
+project.excludeFilters += scala-3
 project.git = true
 rewrite.rules = [ AvoidInfix, ExpandImportSelectors, RedundantParens, SortModifiers, PreferCurlyFors ]
 rewrite.neverInfix.excludeFilters = [
@@ -19,4 +20,4 @@ version = 2.3.2
 
 literals.long=Upper
 literals.float=Upper
-literals.double=Upper
+literals.double=Upper

.travis.yml

@@ -41,6 +41,12 @@ jobs:
         - SCALA_VERSION=2.13.4
         - TRAVIS_JDK=8
 
+    - name: "Run tests with Scala 3 and AdoptOpenJDK 8"
+      script: scripts/test-code.sh
+      env:
+        - SCALA_VERSION=3.0.0-M3
+        - TRAVIS_JDK=8
+
     - stage: publish
       name: "Publish artifacts to Bintray"
       script: sbt +publish

benchmarks/src/main/scala/play/api/libs/json/Employee.scala

@@ -23,7 +23,7 @@ object Employee {
       "lastName" -> e.lastName,
       "city" -> e.city,
       "country" -> e.country,
-      "tags" -> JsArray(e.tags.map(JsString.apply))
+      "tags" -> JsArray(e.tags.map(JsString.apply _))
     )
   }
 

build.sbt

@@ -12,10 +12,11 @@ import sbtcrossproject.CrossType
 
 resolvers ++= DefaultOptions.resolvers(snapshot = true)
 
-val specs2 = Seq(
-  "org.specs2" %% "specs2-core"  % "4.10.5" % Test,
-  "org.specs2" %% "specs2-junit" % "4.10.5" % Test,
-)
+def specs2(scalaVersion: String) =
+  Seq(
+    "org.specs2" %% "specs2-core"  % "4.10.5" % Test,
+    "org.specs2" %% "specs2-junit" % "4.10.5" % Test,
+  ).map(_.withDottyCompat(scalaVersion))
 
 val jacksonDatabindVersion = "2.10.5.1"
 val jacksonDatabind = Seq(
@@ -34,7 +35,7 @@ val joda = Seq(
   "joda-time" % "joda-time" % "2.10.8"
 )
 
-def jsonDependencies(scalaVersion: String) = Seq(
+def scalaReflect(scalaVersion: String) = Seq(
   "org.scala-lang" % "scala-reflect" % scalaVersion
 )
 
@@ -43,6 +44,7 @@ def jsonDependencies(scalaVersion: String) = Seq(
 // Do not check for previous JS artifacts for upgrade to Scala.js 1.0 because no sjs1 artifacts exist
 def playJsonMimaSettings = Seq(
   mimaPreviousArtifacts := ((crossProjectPlatform.?.value, previousStableVersion.value) match {
+    case _ if isDotty.value                => Set.empty // no releases for Scala 3 yet
     case (Some(JSPlatform), Some("2.8.1")) => Set.empty
     case (_, Some(previousVersion))        => Set(organization.value %%% moduleName.value % previousVersion)
     case _                                 => throw new Error("Unable to determine previous version")
@@ -64,6 +66,7 @@ val javacSettings = Seq(
 )
 
 val scalacOpts = Seq(
+  "-language:higherKinds",
   "-target:jvm-1.8",
   "-Ywarn-unused:imports",
   "-Xlint:nullary-unit",
@@ -74,10 +77,14 @@ val scalacOpts = Seq(
 
 val silencerVersion = "1.7.1"
 
-libraryDependencies in ThisBuild ++= Seq(
-  compilerPlugin(("com.github.ghik" % "silencer-plugin" % silencerVersion).cross(CrossVersion.full)),
-  ("com.github.ghik" % "silencer-lib" % silencerVersion % Provided).cross(CrossVersion.full)
-)
+libraryDependencies in ThisBuild ++= {
+  if (isDotty.value) Nil
+  else
+    Seq(
+      compilerPlugin(("com.github.ghik" % "silencer-plugin" % silencerVersion).cross(CrossVersion.full)),
+      ("com.github.ghik" % "silencer-lib" % silencerVersion % Provided).cross(CrossVersion.full)
+    )
+}
 
 // Customise sbt-dynver's behaviour to make it work with tags which aren't v-prefixed
 dynverVTagPrefix in ThisBuild := false
@@ -104,12 +111,12 @@ lazy val commonSettings = Def.settings(
     Tests.Argument(TestFrameworks.ScalaTest, "-l", "play.api.libs.json.UnstableInScala213")
   ),
   headerLicense := Some(HeaderLicense.Custom(s"Copyright (C) 2009-2020 Lightbend Inc. <https://www.lightbend.com>")),
-  scalaVersion := Dependencies.Scala212,
-  crossScalaVersions := Seq(Dependencies.Scala212, Dependencies.Scala213),
+  scalaVersion := Dependencies.Scala3, // 212,
+  crossScalaVersions := Seq(Dependencies.Scala212, Dependencies.Scala213, Dependencies.Scala3),
   javacOptions in Compile ++= javacSettings,
   javacOptions in Test ++= javacSettings,
   javacOptions in (Compile, compile) ++= Seq("-target", "1.8"), // sbt #1785, avoids passing to javadoc
-  scalacOptions ++= scalacOpts,
+  scalacOptions ++= (if (isDotty.value) Nil else scalacOpts),
   scalacOptions in (Compile, doc) ++= Seq(
     // Work around 2.12 bug which prevents javadoc in nested java classes from compiling.
     "-no-java-comments",
@@ -136,28 +143,46 @@ lazy val `play-json` = crossProject(JVMPlatform, JSPlatform)
   .enablePlugins(Omnidoc, Publish, Playdoc)
   .configs(Docs)
   .settings(
-    commonSettings ++ playJsonMimaSettings ++ Seq(
-      libraryDependencies ++= jsonDependencies(scalaVersion.value) ++ Seq(
-        "org.scalatest"     %%% "scalatest"       % "3.1.2"            % Test, // 3.1.2 is the last version that uses Scala.js 1.0.x
-        "org.scalatestplus" %%% "scalacheck-1-14" % "3.1.2.0"          % Test,
-        "org.scalacheck"    %%% "scalacheck"      % "1.14.3"           % Test,
-        "com.chuusai"       %% "shapeless"        % "2.3.3"            % Test,
-        "org.scala-lang"    % "scala-compiler"    % scalaVersion.value % "provided"
-      ),
+    commonSettings ++ playJsonMimaSettings ++ Def.settings(
+      libraryDependencies ++= (if (isDotty.value) Nil else scalaReflect(scalaVersion.value)),
+      libraryDependencies ++= Seq(
+        "org.scalatest"     %%% "scalatest"       % "3.2.3"   % Test,
+        "org.scalatestplus" %%% "scalacheck-1-14" % "3.2.2.0" % Test,
+        "org.scalacheck"    %%% "scalacheck"      % "1.14.3"  % Test,
+        "com.chuusai"       %% "shapeless"        % "2.3.3"   % Test,
+      ).map(_.withDottyCompat(scalaVersion.value)),
+      libraryDependencies += {
+        if (isDotty.value)
+          "org.scala-lang" %% "scala3-compiler" % scalaVersion.value % Provided
+        else
+          "org.scala-lang" % "scala-compiler" % scalaVersion.value % Provided
+      },
       libraryDependencies ++=
         (CrossVersion.partialVersion(scalaVersion.value) match {
           case Some((2, 13)) => Seq()
+          case Some((3, _))  => Nil
           case _             => Seq(compilerPlugin(("org.scalamacros" % "paradise" % "2.1.1").cross(CrossVersion.full)))
         }),
       unmanagedSourceDirectories in Compile += {
         //val sourceDir = (sourceDirectory in Compile).value
         // ^ gives jvm/src/main, for some reason
         val sourceDir = baseDirectory.value.getParentFile / "shared/src/main"
         CrossVersion.partialVersion(scalaVersion.value) match {
-          case Some((2, n)) if n >= 13 => sourceDir / "scala-2.13+"
-          case _                       => sourceDir / "scala-2.13-"
+          case Some((2, n)) if n < 13 => sourceDir / "scala-2.13-"
+          case _                      => sourceDir / "scala-2.13+"
         }
       },
+      Seq((Compile, "main"), (Test, "test")).map {
+        case (conf, dir) =>
+          conf / unmanagedSourceDirectories ++= {
+            val sourceDir = baseDirectory.value.getParentFile / s"shared/src/$dir"
+            CrossVersion.partialVersion(scalaVersion.value) match {
+              case Some((2, _)) => List(sourceDir / "scala-2")
+              case Some((3, _)) => List(sourceDir / "scala-3")
+              case _            => Nil
+            }
+          },
+      },
       sourceGenerators in Compile += Def.task {
         val dir = (sourceManaged in Compile).value
 
@@ -218,7 +243,7 @@ lazy val `play-jsonJS` = `play-json`.js
 
 lazy val `play-jsonJVM` = `play-json`.jvm.settings(
   libraryDependencies ++=
-    jacksons ++ specs2 :+ (
+    jacksons ++ specs2(scalaVersion.value) :+ (
       "ch.qos.logback" % "logback-classic" % "1.2.3" % Test
     ),
   unmanagedSourceDirectories in Test ++= (baseDirectory.value.getParentFile.getParentFile / "docs/manual/working/scalaGuide" ** "code").get
@@ -229,7 +254,7 @@ lazy val `play-json-joda` = project
   .enablePlugins(Omnidoc, Publish)
   .settings(
     commonSettings ++ playJsonMimaSettings ++ Seq(
-      libraryDependencies ++= joda ++ specs2
+      libraryDependencies ++= joda ++ specs2(scalaVersion.value),
     )
   )
   .dependsOn(`play-jsonJVM`)
@@ -260,7 +285,8 @@ lazy val docs = project
   .configs(Docs)
   .settings(
     publish / skip := true,
-    libraryDependencies ++= specs2,
+    libraryDependencies ++= specs2(scalaVersion.value),
+    PlayDocsKeys.validateDocs := (if (isDotty.value) () else PlayDocsKeys.validateDocs.value),
     PlayDocsKeys.scalaManualSourceDirectories := (baseDirectory.value / "manual" / "working" / "scalaGuide" ** "code").get,
     PlayDocsKeys.resources += {
       val apiDocs = (doc in (`play-jsonJVM`, Compile)).value