-Vcyclic to trace locked symbols

Author: som-snytt

src/compiler/scala/tools/nsc/Global.scala

@@ -90,6 +90,8 @@ class Global(var currentSettings: Settings, reporter0: Reporter)
 
   override def settings = currentSettings
 
+  override def isSymbolLockTracingEnabled = settings.cyclic
+
   private[this] var currentReporter: FilteringReporter = null
   locally { reporter = reporter0 }
 

src/compiler/scala/tools/nsc/settings/ScalaSettings.scala

@@ -563,6 +563,7 @@ trait ScalaSettings extends StandardScalaSettings with Warnings { _: MutableSett
    */
   val Vhelp              = BooleanSetting("-V", "Print a synopsis of verbose options.")
   val browse          = PhasesSetting("-Vbrowse", "Browse the abstract syntax tree after") withAbbreviation "-Ybrowse"
+  val cyclic          = BooleanSetting("-Vcyclic", "Debug cyclic reference error.")
   val debug           = BooleanSetting("-Vdebug", "Increase the quantity of debugging output.") withAbbreviation "-Ydebug" withPostSetHook (s => if (s.value) StatisticsStatics.enableDebugAndDeoptimize())
   val YdebugTasty     = BooleanSetting("-Vdebug-tasty", "Increase the quantity of debugging output when unpickling tasty.") withAbbreviation "-Ydebug-tasty"
   val VdebugTypeError = BooleanSetting("-Vdebug-type-error", "Print the stack trace when any error is caught.") withAbbreviation "-Ydebug-type-error"

src/reflect/scala/reflect/internal/SymbolTable.scala

@@ -95,6 +95,8 @@ abstract class SymbolTable extends macros.Universe
 
   def settings: MutableSettings
 
+  def isSymbolLockTracingEnabled: Boolean = isDeveloper
+
   /** Override with final implementation for inlining. */
   def debuglog(msg:  => String): Unit = if (settings.isDebug) log(msg)
 

src/reflect/scala/reflect/internal/Symbols.scala

@@ -45,7 +45,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
   def lockedCount_=(i: Int) = _lockedCount = i
 
   private[this] val _lockingTrace = Stack.empty[Symbol]
-
+  private[this] val lockTracing: Boolean = self.isSymbolLockTracingEnabled
 
   @deprecated("Global existential IDs no longer used", "2.12.1")
   private[this] var existentialIds = 0
@@ -568,7 +568,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
 
     // Lock a symbol, using the handler if the recursion depth becomes too great.
     private[scala] def lock(handler: => Unit): Boolean = {
-      _lockingTrace.push(this)
+      if (lockTracing) _lockingTrace.push(this)
       if ((_rawflags & LOCKED) != 0L) {
         if (settings.Yrecursion.value != 0) {
           recursionTable.get(this) match {
@@ -598,7 +598,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     private[scala] def unlock(): Unit =
       if ((_rawflags & LOCKED) != 0L) {
         _rawflags &= ~LOCKED
-        if (!_lockingTrace.isEmpty)
+        if (lockTracing && !_lockingTrace.isEmpty)
           _lockingTrace.remove(idx = 0, count = 1)
         if (settings.Yrecursion.value != 0)
           recursionTable -= this
@@ -1563,12 +1563,16 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
       if ((_rawflags & LOCKED) != 0L) { // rolled out once for performance
         lock {
           setInfo(ErrorType)
-          val trace = _lockingTrace.toList
-          _lockingTrace.clear()
+          val trace =
+            if (lockTracing) {
+              val t = _lockingTrace.toList
+              _lockingTrace.clear()
+              t
+            } else Nil
           throw CyclicReference(this, tp, trace)
         }
       } else {
-        _lockingTrace.push(this)
+        if (lockTracing) _lockingTrace.push(this)
         _rawflags |= LOCKED
       }
       val current = phase

test/files/neg/t7808.scala

@@ -1,4 +1,4 @@
-
+//> using options -Vcyclic
 class C {
   type OI = Option[Int]
   def f(z: OI, ls: List[OI], rs: List[OI]): (List[OI], List[OI]) = {

test/files/neg/t7808b.check

@@ -0,0 +1,4 @@
+t7808b.scala:5: error: recursive value x$1 needs type
+    val (ls, rs) = z match {
+         ^
+1 error

test/files/neg/t7808b.scala

@@ -0,0 +1,18 @@
+
+class C {
+  type OI = Option[Int]
+  def f(z: OI, ls: List[OI], rs: List[OI]): (List[OI], List[OI]) = {
+    val (ls, rs) = z match {
+      case Some(_) => (z::ls, rs)
+      case _       => (ls, z::rs)
+    }
+    (ls, rs)
+  }
+}
+
+/*
+t7808.scala:5: error: recursive value x$1 needs type
+    val (ls, rs) = z match {
+         ^
+1 error
+*/