Handle Scala LTS and Next version updates

modules/core/src/main/scala/org/scalasteward/core/data/package.scala

@@ -19,14 +19,23 @@ package org.scalasteward.core
 package object data {
   val scalaLangGroupId: GroupId = GroupId("org.scala-lang")
 
-  val scalaLangModules: List[(GroupId, ArtifactId)] =
+  val scala2LangModules: List[(GroupId, ArtifactId)] =
     List(
       (scalaLangGroupId, ArtifactId("scala-compiler")),
       (scalaLangGroupId, ArtifactId("scala-library")),
       (scalaLangGroupId, ArtifactId("scala-reflect")),
-      (scalaLangGroupId, ArtifactId("scalap")),
+      (scalaLangGroupId, ArtifactId("scalap"))
+    )
+
+  val scala3LangModules: List[(GroupId, ArtifactId)] =
+    List(
       (scalaLangGroupId, ArtifactId("scala3-compiler")),
       (scalaLangGroupId, ArtifactId("scala3-library")),
       (scalaLangGroupId, ArtifactId("scala3-library_sjs1"))
     )
+
+  val scalaLangModules: List[(GroupId, ArtifactId)] =
+    scala2LangModules ++ scala3LangModules
+
+  val scalaNextMinVersion: Version = Version("3.4.0")
 }

modules/core/src/main/scala/org/scalasteward/core/update/FilterAlg.scala

@@ -54,6 +54,7 @@ object FilterAlg {
         case NotAllowedByConfig(_)      => "not allowed by config"
         case NoSuitableNextVersion(_)   => "no suitable next version"
         case VersionOrderingConflict(_) => "version ordering conflict"
+        case IgnoreScalaNext(_)         => "not upgrading from Scala LTS to Next version"
       }
   }
 
@@ -62,9 +63,30 @@ object FilterAlg {
   final case class NotAllowedByConfig(update: Update.ForArtifactId) extends RejectionReason
   final case class NoSuitableNextVersion(update: Update.ForArtifactId) extends RejectionReason
   final case class VersionOrderingConflict(update: Update.ForArtifactId) extends RejectionReason
+  final case class IgnoreScalaNext(update: Update.ForArtifactId) extends RejectionReason
 
   def localFilter(update: Update.ForArtifactId, repoConfig: RepoConfig): FilterResult =
-    repoConfig.updates.keep(update).flatMap(globalFilter(_, repoConfig))
+    repoConfig.updates.keep(update).flatMap(scalaLTSFilter).flatMap(globalFilter(_, repoConfig))
+
+  def scalaLTSFilter(update: Update.ForArtifactId): FilterResult =
+    if (!isScala3Lang(update))
+      Right(update)
+    else {
+      if (update.currentVersion >= scalaNextMinVersion) {
+        // already on Scala Next
+        Right(update)
+      } else {
+        val filteredVersions = update.newerVersions.filterNot(_ >= scalaNextMinVersion)
+        if (filteredVersions.nonEmpty)
+          Right(update.copy(newerVersions = Nel.fromListUnsafe(filteredVersions)))
+        else Left(IgnoreScalaNext(update))
+      }
+    }
+
+  def isScala3Lang(update: Update.ForArtifactId): Boolean =
+    scala3LangModules.exists { case (g, a) =>
+      update.groupId == g && update.artifactIds.exists(_ == a)
+    }
 
   private def globalFilter(update: Update.ForArtifactId, repoConfig: RepoConfig): FilterResult =
     selectSuitableNextVersion(update, repoConfig).flatMap(checkVersionOrdering)

modules/core/src/test/scala/org/scalasteward/core/update/FilterAlgTest.scala

@@ -246,4 +246,30 @@ class FilterAlgTest extends FunSuite {
     val dependency = "org.typelevel".g % ("cats-effect", "cats-effect_2.12").a % "1.0.0"
     assert(isDependencyConfigurationIgnored(dependency.copy(configurations = Some("scalafmt"))))
   }
+
+  test("scalaLTSFilter: LTS, no update") {
+    val update = ("org.scala-lang".g % "scala3-compiler".a % "3.3.2" %> Nel.of("3.4.0")).single
+    assertEquals(scalaLTSFilter(update), Left(IgnoreScalaNext(update)))
+  }
+
+  test("scalaLTSFilter: LTS, filter versions") {
+    val update =
+      ("org.scala-lang".g % "scala3-compiler".a % "3.3.2" %> Nel.of("3.3.3", "3.4.0")).single
+    assertEquals(scalaLTSFilter(update), Right(update.copy(newerVersions = Nel.of("3.3.3".v))))
+  }
+
+  test("scalaLTSFilter: Next") {
+    val update = ("org.scala-lang".g % "scala3-compiler".a % "3.4.0" %> Nel.of("3.4.1")).single
+    assertEquals(scalaLTSFilter(update), Right(update))
+  }
+
+  test("isScala3Lang: true") {
+    val update = ("org.scala-lang".g % "scala3-compiler".a % "3.3.3" %> Nel.of("3.4.0")).single
+    assert(isScala3Lang(update))
+  }
+
+  test("isScala3Lang: false") {
+    val update = ("org.scala-lang".g % "scala-compiler".a % "2.13.11" %> Nel.of("2.13.12")).single
+    assert(!isScala3Lang(update))
+  }
 }