add Scala 3 to crossbuild

Author: SethTisue

.travis.yml

@@ -5,6 +5,7 @@ import: scala/scala-dev:travis/default.yml
 language: scala
 
 scala:
+  - 3.0.0-RC1
   - 2.11.12
   - 2.12.13
   - 2.13.5

build.sbt

@@ -73,10 +73,11 @@ lazy val scalaJava8Compat = (project in file("."))
 
     libraryDependencies += "com.novocode" % "junit-interface" % "0.11" % "test",
 
-    // we're still in 0.x land so we could choose to break bincompat,
-    // but let's at least be aware when we're doing it. also we should
-    // think about going 1.0, it's been a while
-    scalaModuleMimaPreviousVersion := Some("0.9.1"),
+    scalaModuleMimaPreviousVersion := {
+      // pending resolution of https://github.com/scalacenter/sbt-version-policy/issues/62
+      if (isDotty.value) None
+      else Some("0.9.1")
+    },
 
     mimaBinaryIssueFilters ++= {
       import com.typesafe.tools.mima.core._, ProblemFilters._
@@ -146,8 +147,14 @@ lazy val scalaJava8Compat = (project in file("."))
         },
         JavaDoc / javacOptions := Seq("-Xdoclint:none"),
         JavaDoc / packageDoc / artifactName := ((sv, mod, art) => "" + mod.name + "_" + sv.binary + "-" + mod.revision + "-javadoc.jar"),
-        libraryDependencies += compilerPlugin("com.typesafe.genjavadoc" % "genjavadoc-plugin" % "0.16" cross CrossVersion.full),
-        Compile / scalacOptions += "-P:genjavadoc:out=" + (target.value / "java")
+        libraryDependencies ++= (
+          if (isDotty.value) Seq()
+          else Seq(compilerPlugin("com.typesafe.genjavadoc" % "genjavadoc-plugin" % "0.16" cross CrossVersion.full))
+        ),
+        Compile / scalacOptions ++= (
+          if (isDotty.value) Seq()
+          else Seq(s"""-P:genjavadoc:out=${target.value / "java"}""")
+        ),
       )
     }
   )

project/plugins.sbt

@@ -1,2 +1,3 @@
 addSbtPlugin("org.scala-lang.modules" % "sbt-scala-module" % "2.2.4")
 addSbtPlugin("ch.epfl.scala" % "sbt-version-policy" % "1.0.0-RC5")
+addSbtPlugin("ch.epfl.lamp" % "sbt-dotty" % "0.5.3")