Changed handling of selection prototypes.

Several changes:

1) Selection prototypes now get treated specially in subtype checks to account for def vs val, polymorphism, etc.
2) Selection prototypes will never nest , so quadratic blowup of checking them is avoided.
3) Selection prototypes are never generated for constructor names.

3 files changed, 27 insertions, 5 deletions

diff --git a/src/dotty/tools/dotc/core/TypeComparer.scala b/src/dotty/tools/dotc/core/TypeComparer.scala
index 2940f949a..17204bf1c 100644
--- a/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -184,7 +184,7 @@ class TypeComparer(implicit val ctx: Context) extends DotClass {
     case tp2: RefinedType =>
       isSubType(tp1, tp2.parent) && (
         tp2.refinedName == nme.WILDCARD ||
-        isSubType(tp1.member(tp2.refinedName).info, tp2.refinedInfo))
+        tp2.matchesInfo(tp1.member(tp2.refinedName).info))
     case AndType(tp21, tp22) =>
       isSubType(tp1, tp21) && isSubType(tp1, tp22)
     case OrType(tp21, tp22) =>
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 1bc8f1646..e263cf076 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -1376,6 +1376,11 @@ object Types {
 
     override def underlying(implicit ctx: Context) = parent
 
+    /** Does goves type match `refinedInfo`. Translates to a subtype check here,
+     *  but is overridden in SelectionProto
+     */
+    def matchesInfo(tp: Type)(implicit ctx: Context): Boolean = tp <:< refinedInfo
+
     def derivedRefinedType(parent: Type, refinedName: Name, refinedInfo: Type)(implicit ctx: Context): RefinedType = {
       def originalName = parent.typeParams.apply(refinedName.hkParamIndex).name
       if ((parent eq this.parent) && (refinedName eq this.refinedName) && (refinedInfo eq this.refinedInfo))
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 7f2ba2959..435e4014a 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -20,7 +20,7 @@ import NameOps._
 import Flags._
 import Decorators._
 import ErrorReporting._
-import Applications.{FunProtoType, PolyProtoType}
+import Applications.{FunProtoType, PolyProtoType, Compatibility, normalize}
 import EtaExpansion.etaExpand
 import util.Positions._
 import util.SourcePosition
@@ -58,7 +58,24 @@ object Typer {
     }
   }
 
-  class SelectionProto(name: Name, tp: Type) extends RefinedType(WildcardType, name)(_ => tp)
+  class SelectionProto(name: Name, tp: Type) extends RefinedType(WildcardType, name)(_ => tp) with Compatibility {
+    override def viewExists(tp: Type, pt: Type)(implicit ctx: Context): Boolean = false
+    override def matchesInfo(tp: Type)(implicit ctx: Context) = {
+      def test(implicit ctx: Context) =
+        isCompatible(normalize(tp), /*(new WildApprox) apply (needed?)*/ refinedInfo)
+      test(ctx.fresh.withNewTyperState)
+    }
+  }
+
+  def selectionProto(name: Name, tp: Type) =
+    if (name.isConstructorName) WildcardType
+    else {
+      val rtp = tp match {
+        case tp: SelectionProto => WildcardType
+        case _ => tp
+      }
+      new SelectionProto(name, rtp)
+    }
 
   object AnySelectionProto extends SelectionProto(nme.WILDCARD, WildcardType)
 }
@@ -327,7 +344,7 @@ class Typer extends Namer with Applications with Implicits {
   }
 
   def typedSelect(tree: untpd.Select, pt: Type)(implicit ctx: Context): Tree = {
-    val qual1 = typedExpr(tree.qualifier, new SelectionProto(tree.name, pt))
+    val qual1 = typedExpr(tree.qualifier, selectionProto(tree.name, pt))
     val ownType = checkedSelectionType(qual1, tree)
     checkValue(ownType, pt, tree.pos)
     cpy.Select(tree, qual1, tree.name).withType(ownType)
@@ -613,7 +630,7 @@ class Typer extends Namer with Applications with Implicits {
   }
 
   def typedSelectFromTypeTree(tree: untpd.SelectFromTypeTree, pt: Type)(implicit ctx: Context): SelectFromTypeTree = {
-    val qual1 = typedType(tree.qualifier, new SelectionProto(tree.name, pt))
+    val qual1 = typedType(tree.qualifier, selectionProto(tree.name, pt))
     cpy.SelectFromTypeTree(tree, qual1, tree.name).withType(checkedSelectionType(qual1, tree))
   }