More comments in Recheck

Author: odersky

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

@@ -155,8 +155,14 @@ abstract class Recheck extends Phase, SymTransformer:
      */
     def keepType(tree: Tree): Boolean = keepAllTypes
 
+    /** A map from NamedTypes to the denotations they had before this phase.
+     *  Needed so that we can `reset` them after this phase.
+     */
     private val prevSelDenots = util.HashMap[NamedType, Denotation]()
 
+    /** Reset all references in `prevSelDenots` to the denotations they had
+     *  before this phase.
+     */
     def reset()(using Context): Unit =
       for (ref, mbr) <- prevSelDenots.iterator do
         ref.withDenot(mbr)
@@ -203,14 +209,14 @@ abstract class Recheck extends Phase, SymTransformer:
             val prevDenot = prevType.denot
             val newType = qualType.select(name, mbr)
             if (newType eq prevType) && (mbr.info ne prevDenot.info) && !prevSelDenots.contains(prevType) then
+              // remember previous denot of NamedType, so that it can be reset after this phase
               prevSelDenots(prevType) = prevDenot
             newType
           case _ =>
             qualType.select(name, mbr)
         constFold(tree, newType)
           //.showing(i"recheck select $qualType . $name : ${mbr.info} = $result")
 
-
     /** Keep the symbol of the `select` but re-infer its type */
     def recheckSelection(tree: Select, qualType: Type, name: Name, pt: Type)(using Context): Type =
       recheckSelection(tree, qualType, name, sharpen = identity[Denotation])