Avoid creating a local dummy when retyping.

Retyping should not create new symbols and that includes local dummys.

Author: odersky

src/dotty/tools/dotc/typer/ReTyper.scala

@@ -3,7 +3,7 @@ package typer
 
 import core.Contexts._
 import core.Types._
-import core.Symbols.Symbol
+import core.Symbols._
 import typer.ProtoTypes._
 import ast.{tpd, untpd}
 import ast.Trees._
@@ -48,6 +48,8 @@ class ReTyper extends Typer {
     untpd.cpy.Bind(tree, tree.name, body1).withType(tree.typeOpt)
   }
 
+  override def localDummy(cls: ClassSymbol, impl: untpd.Template)(implicit ctx: Context) = impl.symbol
+
   override def retrieveSym(tree: untpd.Tree)(implicit ctx: Context): Symbol = tree.symbol
 
   override def localTyper(sym: Symbol) = this

src/dotty/tools/dotc/typer/Typer.scala

@@ -809,11 +809,11 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     val parents1 = ensureConstrCall(ensureFirstIsClass(
         parents mapconserve typedParent, cdef.pos.toSynthetic))
     val self1 = typed(self)(ctx.outer).asInstanceOf[ValDef] // outer context where class memebers are not visible
-    val localDummy = ctx.newLocalDummy(cls, impl.pos)
-    val body1 = typedStats(body, localDummy)(inClassContext(self1.symbol))
+    val dummy = localDummy(cls, impl)
+    val body1 = typedStats(body, dummy)(inClassContext(self1.symbol))
     checkNoDoubleDefs(cls)
     val impl1 = cpy.Template(impl, constr1, parents1, self1, body1)
-      .withType(localDummy.termRef)
+      .withType(dummy.termRef)
     assignType(cpy.TypeDef(cdef, mods1, name, impl1), cls)
 
     // todo later: check that
@@ -825,6 +825,9 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     // 4. Polymorphic type defs override nothing.
   }
 
+  def localDummy(cls: ClassSymbol, impl: untpd.Template)(implicit ctx: Context): Symbol =
+    ctx.newLocalDummy(cls, impl.pos)
+
   def typedImport(imp: untpd.Import, sym: Symbol)(implicit ctx: Context): Import = track("typedImport") {
     val expr1 = typedExpr(imp.expr, AnySelectionProto)
     checkStable(expr1.tpe, imp.expr.pos)