Revert "Warn when using -language:Scala2Compat"

This reverts commit bd874df.

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 // enable when -language:Scala2compat has been purged from the builds
+      if Feature.enabledBySetting(nme.Scala2Compat) && false then // TODO: enable
         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 */
-  @deprecated object Scala2Compat
+  object Scala2Compat
 
   /** Where imported, auto-tupling is disabled */
   object noAutoTupling

project/Build.scala

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

sbt-dotty/sbt-test/source-dependencies/java-analysis-serialization-error/project/DottyInjectedPlugin.scala

@@ -7,6 +7,6 @@ object DottyInjectedPlugin extends AutoPlugin {
 
   override val projectSettings = Seq(
     scalaVersion := sys.props("plugin.scalaVersion"),
-    scalacOptions += "-source:3.0-migration"
+    scalacOptions += "-language:Scala2CompatCompat"
   )
 }