Bugfix: Restore cached denotations of NamedTypes to their value before cc

This is needed to make -Ycheck work after capture checking

Author: odersky

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

@@ -2338,7 +2338,8 @@ object Types {
       lastDenotation match {
         case lastd0: SingleDenotation =>
           val lastd = lastd0.skipRemoved
-          if (lastd.validFor.runId == ctx.runId && (checkedPeriod != Nowhere)) finish(lastd.current)
+          if lastd.validFor.runId == ctx.runId && checkedPeriod != Nowhere then
+            finish(lastd.current)
           else lastd match {
             case lastd: SymDenotation =>
               if (stillValid(lastd) && (checkedPeriod != Nowhere)) finish(lastd.current)
@@ -2443,6 +2444,8 @@ object Types {
     }
 
     private def checkDenot()(using Context) = {}
+      //if name.toString == "getConstructor" then
+      //  println(i"set denot of $this to ${denot.info}, ${denot.getClass}, ${Phases.phaseOf(denot.validFor.lastPhaseId)} at ${ctx.phase}")
 
     private def checkSymAssign(sym: Symbol)(using Context) = {
       def selfTypeOf(sym: Symbol) =

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

@@ -133,7 +133,9 @@ abstract class Recheck extends Phase, SymTransformer:
     else sym
 
   def run(using Context): Unit =
-    newRechecker().checkUnit(ctx.compilationUnit)
+    val rechecker = newRechecker()
+    rechecker.checkUnit(ctx.compilationUnit)
+    rechecker.reset()
 
   def newRechecker()(using Context): Rechecker
 
@@ -153,6 +155,12 @@ abstract class Recheck extends Phase, SymTransformer:
      */
     def keepType(tree: Tree): Boolean = keepAllTypes
 
+    private val prevSelDenots = util.HashMap[NamedType, Denotation]()
+
+    def reset()(using Context): Unit =
+      for (ref, mbr) <- prevSelDenots.iterator do
+        ref.withDenot(mbr)
+
     /** Constant-folded rechecked type `tp` of tree `tree` */
     protected def constFold(tree: Tree, tp: Type)(using Context): Type =
       val tree1 = tree.withType(tp)
@@ -190,7 +198,16 @@ abstract class Recheck extends Phase, SymTransformer:
             qualType.findMember(name, qualType,
               excluded = if tree.symbol.is(Private) then EmptyFlags else Private
           )).suchThat(tree.symbol == _))
-        constFold(tree, qualType.select(name, mbr))
+        val newType = tree.tpe match
+          case prevType: NamedType =>
+            val prevDenot = prevType.denot
+            val newType = qualType.select(name, mbr)
+            if (newType eq prevType) && (mbr.info ne prevDenot.info) && !prevSelDenots.contains(prevType) then
+              prevSelDenots(prevType) = prevDenot
+            newType
+          case _ =>
+            qualType.select(name, mbr)
+        constFold(tree, newType)
           //.showing(i"recheck select $qualType . $name : ${mbr.info} = $result")
 
 

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

@@ -91,7 +91,7 @@ class TreeChecker extends Phase with SymTransformer {
     if (ctx.phaseId <= erasurePhase.id) {
       val initial = symd.initial
       assert(symd == initial || symd.signature == initial.signature,
-        i"""Signature of ${sym.showLocated} changed at phase ${ctx.phase.prevMega}
+        i"""Signature of ${sym} in ${sym.ownersIterator.toList}%, % changed at phase ${ctx.phase.prevMega}
            |Initial info: ${initial.info}
            |Initial sig : ${initial.signature}
            |Current info: ${symd.info}

tests/pos-custom-args/captures/gadt-ycheck.scala

@@ -0,0 +1,14 @@
+package test
+
+import reflect.ClassTag
+import language.experimental.pureFunctions
+
+object Settings:
+  val OptionTag: ClassTag[Option[?]] = ClassTag(classOf[Option[?]])
+
+  class Setting[T: ClassTag](propertyClass: Option[Class[?]]):
+    def tryToSet() =
+      def update(value: Any): String = ???
+      implicitly[ClassTag[T]] match
+        case OptionTag =>
+          update(Some(propertyClass.get.getConstructor().newInstance()))