Setup CI to test on Scala 3.next

.github/workflows/ci.yml

@@ -1,17 +1,20 @@
 name: test
 on:
+  schedule:
+    - cron: '0 0 * * *'
   push:
     branches:
       - main
   pull_request:
 jobs:
-  test:
+  test: &test
     strategy:
       fail-fast: false
       matrix:
         java: [8, 11, 17]
         scala: [2.13.6, 3.0.2]
     runs-on: ubuntu-latest
+    if: ${{ github.event_name != schedule }}
     steps:
     - uses: actions/checkout@v2
       with:
@@ -22,4 +25,13 @@ jobs:
         distribution: temurin
         java-version: ${{matrix.java}}
     - name: Test
-      run: sbt ++${{matrix.scala}} test core/headerCheck package
+      run: sbt "setScalaVersion ${{matrix.scala}}" test core/headerCheck package
+
+  test-rc:
+    <<: *test
+    strategy:
+      fail-fast: false
+      matrix:
+        java: [8]
+        scala: [3.next]
+    if: ${{ github.event_name == schedule }}

build.sbt

@@ -66,3 +66,11 @@ lazy val testmacros = project.in(file("testmacros"))
     }),
     publish / skip := true,
   )
+
+commands += Command.single("setScalaVersion") { (state, arg0) =>
+  val arg = arg0 match {
+    case "3.next" => GetScala3Next.get()
+    case _        => arg0
+  }
+  s"++$arg" :: state
+}

project/GetScala3Next.scala

@@ -0,0 +1,31 @@
+import java.nio.ByteBuffer
+
+import scala.concurrent._, duration._
+
+import gigahorse._, support.okhttp.Gigahorse
+
+import sjsonnew.shaded.scalajson.ast.unsafe._
+import sjsonnew.support.scalajson.unsafe.{ Converter, Parser }
+
+object GetScala3Next {
+  val asJson = (r: FullResponse) => Parser.parseFromByteBuffer(r.bodyAsByteBuffer).get
+
+  def get(): String = {
+    val req = Gigahorse.url("https://api.github.com/repos/lampepfl/dotty/releases")
+        .get.addQueryString("per_page" -> "1")
+
+    val http = Gigahorse.http(Gigahorse.config)
+
+    try {
+      val f = http.run(req, asJson)
+
+      val f2 = f.collect {
+        case JArray(Array(JObject(fields))) => fields.collectFirst {
+          case JField("tag_name", JString(version)) => version
+        }
+      }.map(_.getOrElse(sys.error(s"Expected an array of 1 string, got $j")))
+
+      Await.result(f2, 120.seconds)
+    } finally http.close()
+  }
+}