Add 3.lts and lts scala version option

build.sc

@@ -451,6 +451,7 @@ trait Core extends ScalaCliSbtModule with ScalaCliPublishModule with HasTests
          |  def defaultScalaVersion = "${Scala.defaultUser}"
          |  def defaultScala212Version = "${Scala.scala212}"
          |  def defaultScala213Version = "${Scala.scala213}"
+         |  def scala3Lts = "${Scala.scala3Lts}"
          |
          |  def workspaceDirName = "$workspaceDirName"
          |  def projectFileName = "$projectFileName"

modules/build/src/test/scala/scala/build/tests/BuildOptionsTests.scala

@@ -29,6 +29,8 @@ import scala.build.Directories
 import scala.build.Positioned
 import scala.build.tests.util.BloopServer
 import scala.concurrent.duration.DurationInt
+import scala.build.internal.Regexes.scala3LtsRegex
+import scala.build.errors.ScalaVersionError
 
 class BuildOptionsTests extends TestUtil.ScalaCliBuildSuite {
 
@@ -95,6 +97,21 @@ class BuildOptionsTests extends TestUtil.ScalaCliBuildSuite {
     )
   }
 
+  test(s"Scala 2.lts shows Scala Version Error") {
+
+    val options = BuildOptions(
+      scalaOptions = ScalaOptions(
+        scalaVersion = Some(MaybeScalaVersion(s"3.${Int.MaxValue}"))
+      )
+    )
+    assert(
+      options.projectParams.swap.exists {
+        case _: ScalaVersionError => true; case _ => false
+      },
+      s"specifying 2.lts scala version does not lead to Scala Version Error"
+    )
+  }
+
   test("Scala 2.11.2 shows Unupported Scala Version Error") {
 
     val options = BuildOptions(
@@ -226,6 +243,19 @@ class BuildOptionsTests extends TestUtil.ScalaCliBuildSuite {
     )
   }
 
+  test("-S 3.lts option works") {
+    val options = BuildOptions(
+      scalaOptions = ScalaOptions(
+        scalaVersion = Some(MaybeScalaVersion("3.lts"))
+      )
+    )
+    val scalaParams = options.scalaParams.orThrow.getOrElse(???)
+    assert(
+      scala3LtsRegex.unapplySeq(scalaParams.scalaVersion).isDefined,
+      "-S 3.lts argument does not lead to scala3 LTS"
+    )
+  }
+
   test("-S 2.12.nightly option works") {
     val options = BuildOptions(
       scalaOptions = ScalaOptions(

modules/core/src/main/scala/scala/build/errors/ScalaVersionError.scala

@@ -20,5 +20,6 @@ object ScalaVersionError {
        |In addition, you can request compilation with the last nightly versions of Scala,
        |by passing the 2.nightly, 2.12.nightly, 2.13.nightly, or 3.nightly arguments.
        |Specific Scala 2 or Scala 3 nightly versions are also accepted.
+       |You can also request the latest Scala 3 LTS by passing lts or 3.lts.
        |""".stripMargin
 }

modules/core/src/main/scala/scala/build/internals/Regexes.scala

@@ -3,4 +3,5 @@ package scala.build.internal
 object Regexes {
   val scala2NightlyRegex         = raw"""2\.(\d+)\.(\d+)-bin-[a-f0-9]*""".r
   val scala3NightlyNicknameRegex = raw"""3\.([0-9]*)\.nightly""".r
+  val scala3LtsRegex             = raw"""3\.3\.[0-9]+""".r
 }

modules/options/src/main/scala/scala/build/options/BuildOptions.scala

@@ -330,6 +330,14 @@ final case class BuildOptions(
       case Some(MaybeScalaVersion(Some(svInput))) =>
         val sv = value {
           svInput match {
+            case sv if ScalaVersionUtil.scala3Lts.contains(sv) =>
+              ScalaVersionUtil.validateStable(
+                Constants.scala3Lts,
+                cache,
+                repositories
+              )
+            case sv if ScalaVersionUtil.scala2Lts.contains(sv) =>
+              Left(new ScalaVersionError(s"Invalid Scala version: ${sv}. There is no official LTS version for Scala 2."))
             case sv if sv == ScalaVersionUtil.scala3Nightly =>
               ScalaVersionUtil.GetNightly.scala3(cache)
             case scala3NightlyNicknameRegex(threeSubBinaryNum) =>

modules/options/src/main/scala/scala/build/options/ScalaVersionUtil.scala

@@ -31,6 +31,9 @@ object ScalaVersionUtil {
   def scala212Nightly       = "2.12.nightly"
   def scala213Nightly       = List("2.13.nightly", "2.nightly")
   def scala3Nightly         = "3.nightly"
+  def scala3Lts             = List("3.lts", "lts")
+  // not valid versions, defined only for informative error messages
+  def scala2Lts            = List("2.13.lts", "2.12.lts", "2.lts")
   extension (cache: FileCache[Task]) {
     def fileWithTtl0(artifact: Artifact): Either[ArtifactError, File] =
       cache.logger.use {

project/deps.sc

@@ -5,6 +5,7 @@ object Scala {
   def scala213     = "2.13.12"
   def runnerScala3 = "3.0.2" // the newest version that is compatible with all Scala 3.x versions
   def scala3       = "3.3.1"
+  def scala3Lts    = "3.3" //the full version should be resolved later
 
   // The Scala version used to build the CLI itself.
   def defaultInternal = sys.props.get("scala.version.internal").getOrElse(scala3)