Fix #1037

src/dotty/tools/dotc/config/Config.scala

@@ -4,7 +4,7 @@ object Config {
 
   final val cacheMembersNamed = true
   final val cacheAsSeenFrom = true
-  final val useFingerPrints = true
+  final val useFingerPrints = true // note: it currently seems to be slightly faster not to use them! my junit test: 548s without, 560s with.
   final val cacheMemberNames = true
   final val cacheImplicitScopes = true
 

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

@@ -1250,8 +1250,8 @@ object SymDenotations {
       if (parentIsYounger) {
         incremental.println(s"parents of $this are invalid; symbol id = ${symbol.id}, copying ...\n")
         invalidateInheritedInfo()
-        firstRunId = ctx.runId
       }
+      firstRunId = ctx.runId
       this
     }
 
@@ -1384,7 +1384,7 @@ object SymDenotations {
       var fp = FingerPrint()
       var e = info.decls.lastEntry
       while (e != null) {
-        fp.include(e.sym.name)
+        fp.include(e.name)
         e = e.prev
       }
       var ps = classParents

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

@@ -406,14 +406,17 @@ object Types {
 
     /** The member of this type with the given name  */
     final def member(name: Name)(implicit ctx: Context): Denotation = /*>|>*/ track("member") /*<|<*/ {
-      findMember(name, widenIfUnstable, EmptyFlags)
+      memberExcluding(name, EmptyFlags)
     }
 
     /** The non-private member of this type with the given name. */
     final def nonPrivateMember(name: Name)(implicit ctx: Context): Denotation = track("nonPrivateMember") {
-      findMember(name, widenIfUnstable, Flags.Private)
+      memberExcluding(name, Flags.Private)
     }
 
+    final def memberExcluding(name: Name, excluding: FlagSet)(implicit ctx: Context): Denotation =
+      findMember(name, widenIfUnstable, excluding)
+
     /** Find member of this type with given name and
      *  produce a denotation that contains the type of the member
      *  as seen from given prefix `pre`. Exclude all members that have

src/dotty/tools/dotc/transform/MixinOps.scala

@@ -34,9 +34,14 @@ class MixinOps(cls: ClassSymbol, thisTransform: DenotTransformer)(implicit ctx:
     //sup.select(target)
   }
 
-  /** Is `sym` a member of implementing class `cls`? */
-  def isCurrent(sym: Symbol) = cls.info.member(sym.name).hasAltWith(_.symbol == sym)
-
+  /** Is `sym` a member of implementing class `cls`?
+   *  The test is performed at phase `thisTransform`.
+   */
+  def isCurrent(sym: Symbol) =
+    ctx.atPhase(thisTransform) { implicit ctx =>
+      cls.info.member(sym.name).hasAltWith(_.symbol == sym)
+    }
+
   def needsForwarder(meth: Symbol): Boolean = {
     lazy val overridenSymbols = meth.allOverriddenSymbols
     def needsDisambiguation = !overridenSymbols.forall(_ is Deferred)

tests/run/t7475b.check

@@ -1,2 +1,4 @@
 2
 2
+2
+2

tests/run/t7475b.scala

@@ -1,11 +1,16 @@
 trait A { private val x = 1 }
 trait B { val x = 2 }
+trait C { val x: Int }
 trait C1 extends B with A { println(x) }
 trait C2 extends A with B { println(x) }
+trait C3 extends C with B { println(x) }
+trait C4 extends B with C { println(x) }
 
 object Test {
   def main(args: Array[String]): Unit = {
     new C1 { }
     new C2 { }
+    new C3 { }
+    new C4 { }
   }
 }