New implicit scope scheme

Compute anchors directly instead of relying on namedPartsWith. This
gives more precise control for what is part of the implicit scope.

Author: odersky

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -1540,6 +1540,7 @@ object Trees {
         receiver: tpd.Tree, method: TermName, args: List[Tree], targs: List[Type],
         expectedType: Type)(using parentCtx: Context): tpd.Tree = {
       given ctx as Context = parentCtx.retractMode(Mode.ImplicitsEnabled)
+      import dotty.tools.dotc.ast.tpd.TreeOps
 
       val typer = ctx.typer
       val proto = FunProto(args, expectedType)

compiler/src/dotty/tools/dotc/ast/untpd.scala

@@ -508,7 +508,6 @@ object untpd extends Trees.Instance[Untyped] with UntypedTreeInfo {
   /** A repeated argument such as `arg: _*` */
   def repeated(arg: Tree)(implicit ctx: Context): Typed = Typed(arg, Ident(tpnme.WILDCARD_STAR))
 
-// ----- Accessing modifiers ----------------------------------------------------
 
 // --------- Copier/Transformer/Accumulator classes for untyped trees -----
 

compiler/src/dotty/tools/dotc/core/Types.scala

@@ -5462,14 +5462,15 @@ object Types {
     def apply(x: Unit, tp: Type): Unit = foldOver(p(tp), tp)
   }
 
+  class TypeHashSet extends util.HashSet[Type](64):
+    override def hash(x: Type): Int = System.identityHashCode(x)
+    override def isEqual(x: Type, y: Type) = x.eq(y)
+
   class NamedPartsAccumulator(p: NamedType => Boolean, excludeLowerBounds: Boolean = false)
     (implicit ctx: Context) extends TypeAccumulator[mutable.Set[NamedType]] {
     override def stopAtStatic: Boolean = false
     def maybeAdd(x: mutable.Set[NamedType], tp: NamedType): mutable.Set[NamedType] = if (p(tp)) x += tp else x
-    val seen: util.HashSet[Type] = new util.HashSet[Type](64) {
-      override def hash(x: Type): Int = System.identityHashCode(x)
-      override def isEqual(x: Type, y: Type) = x.eq(y)
-    }
+    val seen = TypeHashSet()
     def apply(x: mutable.Set[NamedType], tp: Type): mutable.Set[NamedType] =
       if (seen contains tp) x
       else {