From 7ca40215f51a7a008dd1856b9813eabfd8121d8d Mon Sep 17 00:00:00 2001
From: Martin Odersky <odersky@gmail.com>
Date: Thu, 14 Nov 2013 18:27:17 +0100
Subject: Making as seenfrom reduce types.

Adding operattions select, derivedSelect which reduce combinations of typerefs over refinement types.
---
 src/dotty/tools/dotc/core/TypeOps.scala | 22 ++++++----------------
 src/dotty/tools/dotc/core/Types.scala   | 32 ++++++++++++++++----------------
 2 files changed, 22 insertions(+), 32 deletions(-)

(limited to 'src/dotty/tools/dotc/core')

diff --git a/src/dotty/tools/dotc/core/TypeOps.scala b/src/dotty/tools/dotc/core/TypeOps.scala
index 8d05a4324..c48a8e715 100644
--- a/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/src/dotty/tools/dotc/core/TypeOps.scala
@@ -20,26 +20,12 @@ trait TypeOps { this: Context =>
         toPrefix(pre.baseType(cls).normalizedPrefix, cls.owner, thiscls)
     }
 
-    ctx.debugTraceIndented(s"$tp.asSeenFrom($pre, $cls)") { // !!! DEBUG
+    ctx.conditionalTraceIndented(TypeOps.track , s"asSeen ${tp.show} from (${pre.show}, ${cls.show})", show = true) { // !!! DEBUG
       tp match {
         case tp: NamedType =>
           val sym = tp.symbol
           if (sym.isStatic) tp
-          else {
-            val tp1 = tp.derivedNamedType(asSeenFrom(tp.prefix, pre, cls, theMap))
-            // Here's an explanation why we short-circuit instantiated type parameters.
-            // Say you have             This is translated to:
-            //
-            // class List[type T] ==>   class List { type T; val hd: T }
-            // xs: List[Int]      ==>   List { type T = Int }
-            //
-            // Then with the line above, xs.hd would have type xs.T
-            //
-            // But in Scala 2.x, its type is Int, which is the dealiased version
-            // of xs.T. With the logic below, we get the same outcome as for 2.x.
-            if ((tp1 ne tp) && (sym is (TypeParam, butNot = Deferred))) tp1.dealias // todo: why not TypeArgument?
-            else tp1
-          }
+          else tp.derivedSelect(asSeenFrom(tp.prefix, pre, cls, theMap))
         case ThisType(thiscls) =>
           toPrefix(pre, cls, thiscls)
         case _: BoundType | NoPrefix =>
@@ -179,3 +165,7 @@ trait TypeOps { this: Context =>
   }
 }
 
+object TypeOps {
+
+  var track = false // !!!DEBUG
+}
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 14ebba57d..03b55736c 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -679,18 +679,18 @@ object Types {
     }
 
     /** The type <this . name> , reduced if possible */
-    def typeSelect(name: TypeName)(implicit ctx: Context): Type =
-      lookupRefined(this, name) orElse TypeRef(this, name)
+    def select(name: Name)(implicit ctx: Context): Type = {
+      val res = lookupRefined(this, name)
+      if (res.exists) res else NamedType(this, name)
+    }
 
     /** The type <this . name> with given symbol, reduced if possible */
-    def typeSelect(name: TypeName, sym: TypeSymbol)(implicit ctx: Context): Type =
-      lookupRefined(this, name) orElse TypeRef.withSym(this, name, sym)
-
-    /** The type <this . sym> , reduced if possible */
-    def typeSelect(sym: TypeSymbol)(implicit ctx: Context): Type =
-      typeSelect(sym.name, sym)
+    def select(sym: Symbol)(implicit ctx: Context): Type = {
+      val res = lookupRefined(this, sym.name)
+      if (res.exists) res else NamedType.withSym(this, sym)
+    }
 
-    private def lookupRefined(pre: Type, name: TypeName)(implicit ctx: Context): Type = pre.stripTypeVar match {
+    private def lookupRefined(pre: Type, name: Name)(implicit ctx: Context): Type = pre.stripTypeVar match {
       case pre: RefinedType =>
         if (pre.refinedName ne name) lookupRefined(pre.parent, name)
         else pre.refinedInfo match {
@@ -1456,6 +1456,10 @@ object Types {
       if (prefix eq this.prefix) this
       else newLikeThis(prefix)
 
+    def derivedSelect(prefix: Type)(implicit ctx: Context): Type =
+      if (prefix eq this.prefix) this
+      else prefix select this.name
+
     /** Create a NamedType of the same kind as this type, if possible,
      *  but with a new prefix. For HasFixedSym instances another such
      *  instance is only created if the symbol's owner is a base class of
@@ -2335,12 +2339,8 @@ object Types {
 
     /** Map this function over given type */
     def mapOver(tp: Type): Type = tp match {
-      case tp: TypeRef =>
-        val tp1 = tp.reduceTypeRef
-        if (tp1 ne tp) this(tp1) else tp.derivedNamedType(this(tp.prefix))
-
-      case tp: TermRef =>
-        tp.derivedNamedType(this(tp.prefix))
+      case tp: NamedType =>
+        tp.derivedSelect(this(tp.prefix))
 
       case _: ThisType
          | _: BoundType => tp
@@ -2444,7 +2444,7 @@ object Types {
 
     def foldOver(x: T, tp: Type): T = tp match {
       case tp: TypeRef =>
-        val tp1 = tp.reduceTypeRef
+        val tp1 = tp.reduceTypeRef // !!! needed?
         this(x, if (tp1 ne tp) tp1 else tp.prefix)
 
       case tp: TermRef =>
-- 
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