Read minor latest scala version from constants

Author: lwronski

build.sc

@@ -1034,7 +1034,23 @@ class TastyLib(val crossScalaVersion: String) extends ScalaCliCrossSbtModule
       else Nil
     }
   )
+  def constantsFile = T.persistent {
+    val dir  = T.dest / "constants"
+    val dest = dir / "Constants.scala"
+    val code =
+      s"""package scala.build.tastylib.internal
+         |
+         |/** Build-time constants. Generated by mill. */
+         |object Constants {
+         |  def latestSupportedScala = "${Scala.defaultInternal}"
+         |}
+         |""".stripMargin
+    if (!os.isFile(dest) || os.read(dest) != code)
+      os.write.over(dest, code, createFolders = true)
+    PathRef(dir)
+  }
 
+  def generatedSources = super.generatedSources() ++ Seq(constantsFile())
 }
 
 object `local-repo` extends LocalRepo {

modules/tasty-lib/src/main/scala/scala/build/tastylib/TastyVersions.scala

@@ -1,15 +1,13 @@
 package scala.build.tastylib
 
+import scala.build.tastylib.internal.Constants
+
 object TastyVersions {
 
   // Every time tasty version is updated, please update LatestSupportedScala as well!
-  final val MajorVersion: Int        = 28
-  final val MinorVersion: Int        = 1
-  final val ExperimentalVersion: Int = 0
-
   object LatestSupportedScala {
     final val MajorVersion: Int = 3
-    final val MinorVersion: Int = 1
+    final val MinorVersion: Int = Constants.latestSupportedScala.split('.')(1).toInt
   }
 
   def shouldRunPreprocessor(