Support named type parameters

Changes needed to support simple named type parameters.
Not yet implemented: named arguments.

4 files changed, 11 insertions, 3 deletions

diff --git a/src/dotty/tools/dotc/core/Flags.scala b/src/dotty/tools/dotc/core/Flags.scala
index 02b341649..298beaaa7 100644
--- a/src/dotty/tools/dotc/core/Flags.scala
+++ b/src/dotty/tools/dotc/core/Flags.scala
@@ -594,6 +594,8 @@ object Flags {
   /** A private parameter accessor */
   final val PrivateParamAccessor = allOf(Private, ParamAccessor)
 
+  final val NamedTypeParam = allOf(TypeParam, ParamAccessor)
+
   /** A local parameter */
   final val ParamAndLocal = allOf(Param, Local)
 
diff --git a/src/dotty/tools/dotc/core/TypeApplications.scala b/src/dotty/tools/dotc/core/TypeApplications.scala
index df842a1ef..4726a16bb 100644
--- a/src/dotty/tools/dotc/core/TypeApplications.scala
+++ b/src/dotty/tools/dotc/core/TypeApplications.scala
@@ -553,7 +553,7 @@ class TypeApplications(val self: Type) extends AnyVal {
       else if (v < 0 && !(tparam is Local) && !(tparam is ExpandedTypeParam)) TypeBounds.lower(self)
       else
       */
-      else TypeAlias(self, v)
+      TypeAlias(self, v)
   }
 
   /** The type arguments of this type's base type instance wrt. `base`.
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 8595da640..27828c588 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -485,7 +485,13 @@ object Types {
       }
       def goThis(tp: ThisType) = {
         val d = go(tp.underlying)
-        if (d.exists) d
+        if (d.exists)
+          if ((pre eq tp) && d.symbol.is(NamedTypeParam) && (d.symbol.owner eq tp.cls))
+            // If we look for a named type parameter `P` in `C.this.P`, looking up
+            // the fully applied self type of `C` will give as an info the alias type
+            // `P = this.P`. We need to return a denotation with the underlying bounds instead.
+            d.symbol.denot
+          else d
         else
           // There is a special case to handle:
           //   trait Super { this: Sub => private class Inner {} println(this.Inner) }
diff --git a/src/dotty/tools/dotc/parsing/Parsers.scala b/src/dotty/tools/dotc/parsing/Parsers.scala
index bad6b95dc..983ee1ccf 100644
--- a/src/dotty/tools/dotc/parsing/Parsers.scala
+++ b/src/dotty/tools/dotc/parsing/Parsers.scala
@@ -1493,7 +1493,7 @@ object Parsers {
             atPos(modStart, in.offset) {
               if (in.token == TYPE) {
                 in.nextToken()
-                mods | Param
+                mods | Param | ParamAccessor
               } else {
                 if (mods.hasFlags) syntaxError("`type' expected")
                 mods | Param | PrivateLocal