Experimental option -Ybreak-cycles.

Overcomes cycles encountered during classfile parsing
in possibly sketchy fashion.

  "illegal cyclic reference involving class Foo"

is the watchword.  See SI-3809.

5 files changed, 13 insertions, 17 deletions

diff --git a/src/compiler/scala/tools/nsc/Global.scala b/src/compiler/scala/tools/nsc/Global.scala
index cb5e2ad555..fb9539e2b2 100644
--- a/src/compiler/scala/tools/nsc/Global.scala
+++ b/src/compiler/scala/tools/nsc/Global.scala
@@ -1046,6 +1046,12 @@ class Global(var currentSettings: Settings, var reporter: Reporter)
   def currentUnit: CompilationUnit = if (currentRun eq null) NoCompilationUnit else currentRun.currentUnit
   def currentSource: SourceFile    = if (currentUnit.exists) currentUnit.source else lastSeenSourceFile
 
+  override def isPastTyper = (
+       (curRun ne null)
+    && (currentRun.typerPhase ne null)
+    && (globalPhase.id > currentRun.typerPhase.id)
+  )
+
   // TODO - trim these to the absolute minimum.
   @inline final def exitingErasure[T](op: => T): T        = exitingPhase(currentRun.erasurePhase)(op)
   @inline final def exitingPostErasure[T](op: => T): T    = exitingPhase(currentRun.posterasurePhase)(op)
diff --git a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
index 3ff7af791b..4829fb81b5 100644
--- a/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
+++ b/src/compiler/scala/tools/nsc/settings/ScalaSettings.scala
@@ -127,6 +127,7 @@ trait ScalaSettings extends AbsScalaSettings
   val overrideObjects = BooleanSetting    ("-Yoverride-objects", "Allow member objects to be overridden.")
   val overrideVars    = BooleanSetting    ("-Yoverride-vars", "Allow vars to be overridden.")
   val Yhelp           = BooleanSetting    ("-Y", "Print a synopsis of private options.")
+  val breakCycles     = BooleanSetting    ("-Ybreak-cycles", "Attempt to break cycles encountered during classfile parsing")
   val browse          = PhasesSetting     ("-Ybrowse", "Browse the abstract syntax tree after")
   val check           = PhasesSetting     ("-Ycheck", "Check the tree at the end of")
   val Yshow           = PhasesSetting     ("-Yshow", "(Requires -Xshow-class or -Xshow-object) Show after")
diff --git a/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala b/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
index f12f08030b..7c02f094ed 100644
--- a/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/ContextErrors.scala
@@ -657,8 +657,8 @@ trait ContextErrors {
       def CyclicAliasingOrSubtypingError(errPos: Position, sym0: Symbol) =
         issueTypeError(PosAndMsgTypeError(errPos, "cyclic aliasing or subtyping involving "+sym0))
 
-      def CyclicReferenceError(errPos: Position, lockedSym: Symbol) =
-        issueTypeError(PosAndMsgTypeError(errPos, "illegal cyclic reference involving " + lockedSym))
+      def CyclicReferenceError(errPos: Position, tp: Type, lockedSym: Symbol) =
+        issueTypeError(PosAndMsgTypeError(errPos, s"illegal cyclic reference involving $tp and $lockedSym"))
 
       // macro-related errors (also see MacroErrors below)
 
diff --git a/src/compiler/scala/tools/nsc/typechecker/Namers.scala b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
index 9e1a9d6d17..4b60fd8b27 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Namers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Namers.scala
@@ -711,8 +711,9 @@ trait Namers extends MethodSynthesis {
       tp match {
         case TypeBounds(lo, _) =>
           // check that lower bound is not an F-bound
+          // but carefully: class Foo[T <: Bar[_ >: T]] should be allowed
           for (TypeRef(_, sym, _) <- lo)
-            sym.initialize
+            sym.maybeInitialize
         case _ =>
       }
       tp
@@ -731,17 +732,6 @@ trait Namers extends MethodSynthesis {
         if (needsCycleCheck && !typer.checkNonCyclic(tree.pos, tp))
           sym setInfo ErrorType
       }
-      // tree match {
-      //   case ClassDef(_, _, _, impl) =>
-      //     val parentsOK = (
-      //          treeInfo.isInterface(sym, impl.body)
-      //       || (sym eq ArrayClass)
-      //       || (sym isSubClass AnyValClass)
-      //     )
-      //     if (!parentsOK)
-      //       ensureParent(sym, AnyRefClass)
-      //   case _ => ()
-      // }
     }
 
     def moduleClassTypeCompleter(tree: ModuleDef) = {
diff --git a/src/compiler/scala/tools/nsc/typechecker/Typers.scala b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
index 688b4b5160..7a2c64142d 100644
--- a/src/compiler/scala/tools/nsc/typechecker/Typers.scala
+++ b/src/compiler/scala/tools/nsc/typechecker/Typers.scala
@@ -292,8 +292,7 @@ trait Typers extends Modes with Adaptations with Tags {
      */
     def checkNonCyclic(pos: Position, tp: Type): Boolean = {
       def checkNotLocked(sym: Symbol) = {
-        sym.initialize
-        sym.lockOK || { CyclicAliasingOrSubtypingError(pos, sym); false }
+        sym.initialize.lockOK || { CyclicAliasingOrSubtypingError(pos, sym); false }
       }
       tp match {
         case TypeRef(pre, sym, args) =>
@@ -320,7 +319,7 @@ trait Typers extends Modes with Adaptations with Tags {
     }
 
     def checkNonCyclic(pos: Position, tp: Type, lockedSym: Symbol): Boolean = try {
-      if (!lockedSym.lock(CyclicReferenceError(pos, lockedSym))) false
+      if (!lockedSym.lock(CyclicReferenceError(pos, tp, lockedSym))) false
       else checkNonCyclic(pos, tp)
     } finally {
       lockedSym.unlock()