Fix DenotTransformer#validFor

This method was unused so far but will be used in the next commit. The
validity period of a transformed denotation starts at the phase after
the transformer has been run.

Author: smarter

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

@@ -24,9 +24,9 @@ object DenotTransformers {
     /** The last phase during which the transformed denotations are valid */
     def lastPhaseId(implicit ctx: Context) = ctx.nextDenotTransformerId(id + 1)
 
-    /** The validity period of the transformer in the given context */
+    /** The validity period of the transformed denotations in the given context */
     def validFor(implicit ctx: Context): Period =
-      Period(ctx.runId, id, lastPhaseId)
+      Period(ctx.runId, id + 1, lastPhaseId)
 
     /** The transformation method */
     def transform(ref: SingleDenotation)(implicit ctx: Context): SingleDenotation

compiler/src/dotty/tools/dotc/transform/ExtensionMethods.scala

@@ -62,8 +62,6 @@ class ExtensionMethods extends MiniPhase with DenotTransformer with FullParamete
           val decls1 = cinfo.decls.cloneScope
           val moduleSym = moduleClassSym.symbol.asClass
 
-          var newSuperClass: Type = null
-
           ctx.atPhase(thisPhase.next) { implicit ctx =>
             // In Scala 2, extension methods are added before pickling so we should
             // not generate them again.