Warn when using -language:Scala2Compat

Author: odersky

compiler/src/dotty/tools/dotc/Driver.scala

@@ -75,7 +75,7 @@ class Driver {
     inContext(ictx) {
       if !ctx.settings.YdropComments.value || ctx.mode.is(Mode.ReadComments) then
         ictx.setProperty(ContextDoc, new ContextDocstrings)
-      if Feature.enabledBySetting(nme.Scala2Compat) && false then // TODO: enable
+      if Feature.enabledBySetting(nme.Scala2Compat) then
         ctx.warning("-language:Scala2Compat will go away; use -source 3.0-migration instead")
       val fileNames = CompilerCommand.checkUsage(summary, sourcesRequired)
       fromTastySetup(fileNames, ctx)

library/src/scalaShadowing/language.scala

@@ -213,7 +213,7 @@ object language {
   }
 
   /** Where imported, a backwards compatibility mode for Scala2 is enabled */
-  object Scala2Compat
+  @deprecated object Scala2Compat
 
   /** Where imported, auto-tupling is disabled */
   object noAutoTupling

project/Build.scala

@@ -783,10 +783,7 @@ object Build {
     )
 
   lazy val tastyCoreSettings = Seq(
-    scalacOptions ~= { old =>
-      val (language, other) = old.partition(_.startsWith("-language:"))
-      other :+ (language.headOption.map(_ + ",Scala2Compat").getOrElse("-source:3.0-migration"))
-    }
+    scalacOptions ~= (_ ++ Seq("-source", "3.0-migration"))
   )
 
   lazy val `tasty-core` = project.in(file("tasty")).asTastyCore(NonBootstrapped)