5 files changed, 18 insertions, 8 deletions
diff --git a/src/dotty/tools/dotc/core/Flags.scala b/src/dotty/tools/dotc/core/Flags.scala
index 0678b79be..620cd4fa5 100644
--- a/src/dotty/tools/dotc/core/Flags.scala
+++ b/src/dotty/tools/dotc/core/Flags.scala
@@ -467,7 +467,7 @@ object Flags {
   final val ExpandedTypeParam = allOf(ExpandedName, TypeParam)
 
   /** A parameter or parameter accessor */
-  final val ParamOrAccessor = Param | Accessor
+  final val ParamOrAccessor = Param | ParamAccessor
 
   /** A covariant type parameter instance */
   final val LocalCovariant = allOf(Local, Covariant)
diff --git a/src/dotty/tools/dotc/core/SymDenotations.scala b/src/dotty/tools/dotc/core/SymDenotations.scala
index 5fbf6c2c4..bbe5cf986 100644
--- a/src/dotty/tools/dotc/core/SymDenotations.scala
+++ b/src/dotty/tools/dotc/core/SymDenotations.scala
@@ -145,9 +145,14 @@ object SymDenotations {
       if (myFlags is Touched) throw new CyclicReference(this)
       myFlags |= Touched
 
-      completions.println(s"completing ${this.debugString}")
-      completer.complete(this)
-      completions.println(s"completed ${this.debugString}")
+      // completions.println(s"completing ${this.debugString}")
+      try completer.complete(this)
+      catch {
+      case ex: CyclicReference =>
+        completions.println(s"error while completing ${this.debugString}")
+        throw ex
+      }
+      // completions.println(s"completed ${this.debugString}")
     }
 
     protected[dotc] final def info_=(tp: Type) = {
diff --git a/src/dotty/tools/dotc/typer/Checking.scala b/src/dotty/tools/dotc/typer/Checking.scala
index 25e6a7aa7..e3024b9a6 100644
--- a/src/dotty/tools/dotc/typer/Checking.scala
+++ b/src/dotty/tools/dotc/typer/Checking.scala
@@ -45,13 +45,16 @@ trait Checking extends NoChecking {
   }
 
   /** Check that type arguments `args` conform to corresponding bounds in `poly` */
-  override def checkBounds(args: List[tpd.Tree], poly: PolyType, pos: Position)(implicit ctx: Context): Unit =
+  override def checkBounds(args: List[tpd.Tree], poly: PolyType, pos: Position)(implicit ctx: Context): Unit = {
+    val argTypes = args.tpes
+    def substituted(tp: Type) = tp.substParams(poly, argTypes)
     for ((arg, bounds) <- args zip poly.paramBounds) {
       def notConforms(which: String, bound: Type) =
         ctx.error(i"Type argument ${arg.tpe} does not conform to $which bound $bound", arg.pos)
-      if (!(arg.tpe <:< bounds.hi)) notConforms("upper", bounds.hi)
+      if (!(arg.tpe <:< substituted(bounds.hi))) notConforms("upper", bounds.hi)
       if (!(bounds.lo <:< arg.tpe)) notConforms("lower", bounds.lo)
     }
+  }
 
   /** Check that type `tp` is stable.
    *  @return The type itself
diff --git a/src/dotty/tools/dotc/typer/Namer.scala b/src/dotty/tools/dotc/typer/Namer.scala
index c24021936..9c8522b83 100644
--- a/src/dotty/tools/dotc/typer/Namer.scala
+++ b/src/dotty/tools/dotc/typer/Namer.scala
@@ -614,6 +614,7 @@ class Namer { typer: Typer =>
 
   def typeDefSig(tdef: TypeDef, sym: Symbol)(implicit ctx: Context): Type = {
     completeParams(tdef.tparams)
+    sym.info = TypeBounds.empty // avoid cyclic reference errors for F-bounds
     val tparamSyms = tdef.tparams map symbolOfTree
     val rhsType = typedAheadType(tdef.rhs).tpe
 
diff --git a/src/dotty/tools/dotc/typer/Typer.scala b/src/dotty/tools/dotc/typer/Typer.scala
index 6a1d279df..e195c2807 100644
--- a/src/dotty/tools/dotc/typer/Typer.scala
+++ b/src/dotty/tools/dotc/typer/Typer.scala
@@ -699,8 +699,9 @@ class Typer extends Namer with TypeAssigner with Applications with Implicits wit
     val TypeBoundsTree(lo, hi) = desugar.typeBoundsTree(tree)
     val lo1 = typed(lo)
     val hi1 = typed(hi)
-    if (!(lo1.tpe <:< hi1.tpe))
-      ctx.error(i"lower bound ${lo1.tpe} does not conform to upper bound ${hi1.tpe}", tree.pos)
+    if (false) // need to do in later phase, as this might cause a cyclic reference error. See pos/t0039.scala
+      if (!(lo1.tpe <:< hi1.tpe))
+        ctx.error(i"lower bound ${lo1.tpe} does not conform to upper bound ${hi1.tpe}", tree.pos)
     assignType(cpy.TypeBoundsTree(tree, lo1, hi1), lo1, hi1)
   }