Introduce recursive types

Map self-references in refinements to recursive types. This
commit does this for refinement types appearing in source.
We still have to do it for unpickled refinements.

Test apply-equiv got moved to pending because it simulates
the old higher-kinded type encoding in source, which relies
on the old representation in terms of self-referential refinement
types. The plan is not to adapt this encoding to the new
representation, but to replace it with a different encoding
that makes critical use of the added power of recursive types.

Use recursive types also when unpickling from Scala 2.x.

Add mapInfo method to Denotations.

1 files changed, 14 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/printing/PlainPrinter.scala b/src/dotty/tools/dotc/printing/PlainPrinter.scala
index 7053a0ea3..59f1608db 100644
--- a/src/dotty/tools/dotc/printing/PlainPrinter.scala
+++ b/src/dotty/tools/dotc/printing/PlainPrinter.scala
@@ -13,6 +13,8 @@ import scala.annotation.switch
 class PlainPrinter(_ctx: Context) extends Printer {
   protected[this] implicit def ctx: Context = _ctx.addMode(Mode.Printing)
 
+  private var openRecs: List[RecType] = Nil
+
   protected def maxToTextRecursions = 100
 
   protected final def controlled(op: => Text): Text =
@@ -58,6 +60,8 @@ class PlainPrinter(_ctx: Context) extends Printer {
       }
     else tp
 
+  private def selfRecName(n: Int) = s"z$n"
+
   /** Render elements alternating with `sep` string */
   protected def toText(elems: Traversable[Showable], sep: String) =
     Text(elems map (_ toText this), sep)
@@ -130,6 +134,12 @@ class PlainPrinter(_ctx: Context) extends Printer {
         val parent :: (refined: List[RefinedType @unchecked]) =
           refinementChain(tp).reverse
         toTextLocal(parent) ~ "{" ~ Text(refined map toTextRefinement, "; ").close ~ "}"
+      case tp: RecType =>
+        try {
+          openRecs = tp :: openRecs
+          "{" ~ selfRecName(openRecs.length) ~ " => " ~ toTextGlobal(tp.parent) ~ "}"
+        }
+        finally openRecs = openRecs.tail
       case AndType(tp1, tp2) =>
         changePrec(AndPrec) { toText(tp1) ~ " & " ~ toText(tp2) }
       case OrType(tp1, tp2) =>
@@ -232,6 +242,10 @@ class PlainPrinter(_ctx: Context) extends Printer {
         toText(value)
       case MethodParam(mt, idx) =>
         nameString(mt.paramNames(idx))
+      case tp: RecThis =>
+        val idx = openRecs.reverse.indexOf(tp.binder)
+        if (idx >= 0) selfRecName(idx + 1)
+        else "{...}.this" // TODO move underlying type to an addendum, e.g. ... z3 ... where z3: ...
       case tp: RefinedThis =>
         s"${nameString(tp.binder.typeSymbol)}{...}.this"
       case tp: SkolemType =>