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.

3 files changed, 20 insertions, 3 deletions

diff --git a/src/dotty/tools/dotc/core/tasty/TastyFormat.scala b/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
index a42958e75..e9708961a 100644
--- a/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
+++ b/src/dotty/tools/dotc/core/tasty/TastyFormat.scala
@@ -103,7 +103,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   TERMREFpkg            fullyQualified_NameRef
                   TERMREF               possiblySigned_NameRef qual_Type
                   THIS                  clsRef_Type
-                  REFINEDthis           refinedType_ASTRef
+                  RECthis               recType_ASTRef
                   SHARED                path_ASTRef
 
   Constant      = UNITconst
@@ -126,6 +126,7 @@ Standard-Section: "ASTs" TopLevelStat*
                   TYPEREFsymbol         sym_ASTRef qual_Type
                   TYPEREFpkg            fullyQualified_NameRef
                   TYPEREF               possiblySigned_NameRef qual_Type
+                  RECtype               parent_Type
                   SUPERtype      Length this_Type underlying_Type
                   REFINEDtype    Length underlying_Type refinement_NameRef info_Type
                   APPLIEDtype    Length tycon_Type arg_Type*
@@ -259,6 +260,7 @@ object TastyFormat {
   final val TERMREFpkg = 67
   final val TYPEREFpkg = 68
   final val REFINEDthis = 69
+  final val RECthis = REFINEDthis // !!!
   final val BYTEconst = 70
   final val SHORTconst = 71
   final val CHARconst = 72
@@ -277,6 +279,7 @@ object TastyFormat {
   final val IMPLICITarg = 101
   final val PRIVATEqualified = 102
   final val PROTECTEDqualified = 103
+  final val RECtype = 104
 
   final val IDENT = 112
   final val SELECT = 113
@@ -417,7 +420,7 @@ object TastyFormat {
     case TYPEREFdirect => "TYPEREFdirect"
     case TERMREFpkg => "TERMREFpkg"
     case TYPEREFpkg => "TYPEREFpkg"
-    case REFINEDthis => "REFINEDthis"
+    case RECthis => "RECthis"
     case BYTEconst => "BYTEconst"
     case SHORTconst => "SHORTconst"
     case CHARconst => "CHARconst"
@@ -426,6 +429,7 @@ object TastyFormat {
     case FLOATconst => "FLOATconst"
     case DOUBLEconst => "DOUBLEconst"
     case STRINGconst => "STRINGconst"
+    case RECtype => "RECtype"
 
     case IDENT => "IDENT"
     case SELECT => "SELECT"
diff --git a/src/dotty/tools/dotc/core/tasty/TreePickler.scala b/src/dotty/tools/dotc/core/tasty/TreePickler.scala
index 0cc08f2d9..9f703b5af 100644
--- a/src/dotty/tools/dotc/core/tasty/TreePickler.scala
+++ b/src/dotty/tools/dotc/core/tasty/TreePickler.scala
@@ -212,6 +212,11 @@ class TreePickler(pickler: TastyPickler) {
       val binderAddr = pickledTypes.get(tpe.binder)
       assert(binderAddr != null, tpe.binder)
       writeRef(binderAddr.asInstanceOf[Addr])
+    case tpe: RecThis =>
+      writeByte(RECthis)
+      val binderAddr = pickledTypes.get(tpe.binder)
+      assert(binderAddr != null, tpe.binder)
+      writeRef(binderAddr.asInstanceOf[Addr])
     case tpe: SkolemType =>
       pickleType(tpe.info)
     case tpe: RefinedType =>
@@ -221,6 +226,9 @@ class TreePickler(pickler: TastyPickler) {
         pickleType(tpe.parent)
         pickleType(tpe.refinedInfo, richTypes = true)
       }
+    case tpe: RecType =>
+      writeByte(RECtype)
+      pickleType(tpe.parent)
     case tpe: TypeAlias =>
       writeByte(TYPEALIAS)
       withLength {
diff --git a/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala b/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
index 2b8e5f019..1b4e7845a 100644
--- a/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
+++ b/src/dotty/tools/dotc/core/tasty/TreeUnpickler.scala
@@ -335,8 +335,13 @@ class TreeUnpickler(reader: TastyReader, tastyName: TastyName.Table) {
           }
         case THIS =>
           ThisType.raw(readType().asInstanceOf[TypeRef])
+        case RECtype =>
+          RecType(rt => registeringType(rt, readType()))
         case REFINEDthis =>
-          RefinedThis(readTypeRef().asInstanceOf[RefinedType])
+          readTypeRef() match {
+            case t: RefinedType => RefinedThis(t)
+            case t: RecType => RecThis(t)
+          }
         case SHARED =>
           val ref = readAddr()
           typeAtAddr.getOrElseUpdate(ref, forkAt(ref).readType())