Workaround #2335 issue in bootstraped REPL

Author: OlivierBlanvillain

compiler/src/dotty/tools/dotc/repl/ammonite/Protocol.scala

@@ -15,12 +15,20 @@ case class TermState(
 ) extends TermAction
 
 object TermState {
+  // Using unapply instead exposes a dotty/scalac variation. Because TermState
+  // is case class, scalac generate an unapply with this exact signature, that
+  // is used by the TermInfo | TermAction unapplies. With dotty, the generated
+  // unapply has type `TermState => TermState` instead, the TermState.unapply
+  // for TermAction thus becomes a infinite tail recursion. See #2335.
+  def unapplyWorkaround(ti: TermState): Option[(LazyList[Int], Vector[Char], Int, Ansi.Str)] =
+    Some((ti.inputs, ti.buffer, ti.cursor, ti.msg))
+
   def unapply(ti: TermInfo): Option[(LazyList[Int], Vector[Char], Int, Ansi.Str)] =
-    TermState.unapply(ti.ts)
+    TermState.unapplyWorkaround(ti.ts)
 
   def unapply(ti: TermAction): Option[(LazyList[Int], Vector[Char], Int, Ansi.Str)] =
     ti match {
-      case ts: TermState => TermState.unapply(ts)
+      case ts: TermState => TermState.unapplyWorkaround(ts)
       case _ => None
     }
 }