Invalidate member caches after completing classes in Namer

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

@@ -1630,7 +1630,11 @@ object SymDenotations {
       myBaseTypeCachePeriod = Nowhere
     }
 
-    def invalidateMemberCaches(sym: Symbol)(using Context): Unit =
+    def invalidateMemberCaches()(using Context): Unit =
+      myMemberCachePeriod = Nowhere
+      invalidateMemberNamesCache()
+
+    def invalidateMemberCachesFor(sym: Symbol)(using Context): Unit =
       if myMemberCache != null then myMemberCache.remove(sym.name)
       if !sym.flagsUNSAFE.is(Private) then
         invalidateMemberNamesCache()
@@ -1831,7 +1835,7 @@ object SymDenotations {
     /** Enter a symbol in given `scope` without potentially replacing the old copy. */
     def enterNoReplace(sym: Symbol, scope: MutableScope)(using Context): Unit =
       scope.enter(sym)
-      invalidateMemberCaches(sym)
+      invalidateMemberCachesFor(sym)
 
     /** Replace symbol `prev` (if defined in current class) by symbol `replacement`.
      *  If `prev` is not defined in current class, do nothing.

compiler/src/dotty/tools/dotc/typer/Namer.scala

@@ -1231,6 +1231,7 @@ class Namer { typer: Typer =>
       if (isDerivedValueClass(cls)) cls.setFlag(Final)
       cls.info = avoidPrivateLeaks(cls)
       cls.baseClasses.foreach(_.invalidateBaseTypeCache()) // we might have looked before and found nothing
+      cls.invalidateMemberCaches() // we might have checked for a member when parents were not known yet.
       cls.setNoInitsFlags(parentsKind(parents), untpd.bodyKind(rest))
       val ctorStable =
         if cls.is(Trait) then cls.is(NoInits)

tests/pos/i10634/AParser.scala

@@ -0,0 +1,2 @@
+case class Parser(ctx: Context) extends BasicSupport
+

tests/pos/i10634/BasicSupport.scala

@@ -0,0 +1,10 @@
+// BasicSupport.scala
+trait BasicSupport:
+  self: Parser =>
+
+  object SymOps extends SymOps[ctx.type](ctx)
+  export SymOps._
+
+  def parse(sym: ctx.Symbol): Int =
+    sym.getVisibility()
+

tests/pos/i10634/Context.scala

@@ -0,0 +1,8 @@
+// Context.scala
+trait Context:
+  type Symbol
+
+trait SymOps[C <: Context](val c: C):
+  extension (sym: c.Symbol)
+    def getVisibility(): Int = 0
+