BestFirstSearch: extract queues into a new class

Move `trackState` into `getActiveSplits` as well, since that is what
should constitute a visit.

scalafmt-core/shared/src/main/scala/org/scalafmt/internal/BestFirstSearch.scala

@@ -87,19 +87,12 @@ private class BestFirstSearch private (range: Set[Range])(implicit
       depth: Int = 0,
       maxCost: Int = Integer.MAX_VALUE,
   ): State = {
-    def newGeneration = new mutable.PriorityQueue[State]()
-    var Q = newGeneration
-    var generations: List[mutable.PriorityQueue[State]] = Nil
-    def addGeneration() = if (Q.nonEmpty) {
-      generations = Q :: generations
-      Q = newGeneration
-    }
-    Q += start
-
+    implicit val Q: StateQueue = new StateQueue(depth)
     def enqueue(state: State) = Q.enqueue(state)
+    enqueue(start)
 
     // TODO(olafur) this while loop is waaaaaaaaaaaaay tooo big.
-    while (true) {
+    while (!Q.isEmpty()) {
       val curr = Q.dequeue()
       if (curr.depth >= tokens.length) return curr
 
@@ -115,8 +108,6 @@ private class BestFirstSearch private (range: Set[Range])(implicit
         noOptZones.contains(leftTok)
 
       if (noOptZone || shouldEnterState(curr)) {
-        trackState(curr, depth, Q.length)
-
         if (explored > style.runner.maxStateVisits) {
           complete(deepestYet)
           throw new Error.SearchStateExploded(
@@ -131,7 +122,7 @@ private class BestFirstSearch private (range: Set[Range])(implicit
             optimizer.dequeueOnNewStatements && curr.allAltAreNL &&
             !(depth == 0 && noOptZone) &&
             (leftTok.is[Token.KwElse] || statementStarts.contains(curr.depth))
-          ) addGeneration()
+          ) Q.addGeneration()
 
         val noBlockClose = start == curr && 0 != maxCost || !noOptZone ||
           !optimizer.recurseOnBlocks
@@ -168,7 +159,7 @@ private class BestFirstSearch private (range: Set[Range])(implicit
                 else shortestPath(nextState, opt.token, depth + 1, maxCost = 0)
               val furtherState =
                 if (null == nextNextState) null
-                else traverseSameLine(nextNextState, depth)
+                else traverseSameLine(nextNextState)
               if (null == furtherState) if (killOnFail(opt)) null else nextState
               else if (
                 furtherState.appliedPenalty > nextNextState.appliedPenalty
@@ -202,24 +193,15 @@ private class BestFirstSearch private (range: Set[Range])(implicit
           }
         }
       }
-
-      if (Q.isEmpty) {
-        if (generations.isEmpty) return null
-
-        Q = generations.head
-        generations = generations.tail
-      }
     }
 
-    // unreachable
     null
   }
 
-  private def getActiveSplits(
-      ft: FormatToken,
-      state: State,
-      maxCost: Int,
+  private def getActiveSplits(ft: FormatToken, state: State, maxCost: Int)(
+      implicit Q: StateQueue,
   ): Seq[Split] = {
+    trackState(state)
     val useProvided = ft.meta.formatOff || !ft.inside(range)
     val active = state.policy.execute(Decision(ft, routes(state.depth)))
       .filter(x => x.isActive && x.cost <= maxCost)
@@ -235,38 +217,38 @@ private class BestFirstSearch private (range: Set[Range])(implicit
     splits.sortBy(_.cost)
   }
 
-  private def trackState(state: State, depth: Int, queueSize: Int)(implicit
-      style: ScalafmtConfig,
-  ): Unit = {
-    if (state.depth > deepestYet.depth) deepestYet = state
-    style.runner.event(FormatEvent.VisitToken(tokens(state.depth)))
-    visits(state.depth) += 1
+  private def trackState(state: State)(implicit Q: StateQueue): Unit = {
+    val idx = state.depth
+    if (idx > deepestYet.depth) deepestYet = state
+    initStyle.runner.event(FormatEvent.VisitToken(tokens(idx)))
+    visits(idx) += 1
     explored += 1
-    style.runner.event(FormatEvent.Explored(explored, depth, queueSize))
+    initStyle.runner.event(FormatEvent.Explored(explored, Q.nested, Q.length))
   }
 
   /** Follow states having single active non-newline split
     */
   @tailrec
-  private def traverseSameLine(state: State, depth: Int): State =
+  private def traverseSameLine(
+      state: State,
+  )(implicit queue: StateQueue): State =
     if (state.depth >= tokens.length) state
     else {
       val splitToken = tokens(state.depth)
       implicit val style: ScalafmtConfig = styleMap.at(splitToken)
-      trackState(state, depth, 0)
       getActiveSplits(splitToken, state, Int.MaxValue) match {
         case Seq() => null // dead end if empty
         case Seq(split) =>
           if (split.isNL) state
           else {
             style.runner.event(FormatEvent.Enqueue(split))
             val nextState = state.next(split, nextAllAltAreNL = false)
-            traverseSameLine(nextState, depth)
+            traverseSameLine(nextState)
           }
         case ss
             if state.appliedPenalty == 0 &&
               RightParenOrBracket(splitToken.right) =>
-          traverseSameLineZeroCost(ss.filter(_.cost == 0), state, depth)
+          traverseSameLineZeroCost(ss.filter(_.cost == 0), state)
         case _ => state
       }
     }
@@ -275,8 +257,7 @@ private class BestFirstSearch private (range: Set[Range])(implicit
   private def traverseSameLineZeroCost(
       splits: Seq[Split],
       state: State,
-      depth: Int,
-  )(implicit style: ScalafmtConfig): State = splits match {
+  )(implicit style: ScalafmtConfig, queue: StateQueue): State = splits match {
     case Seq(split) if !split.isNL =>
       style.runner.event(FormatEvent.Enqueue(split))
       val nextState = state.next(split, nextAllAltAreNL = false)
@@ -286,9 +267,8 @@ private class BestFirstSearch private (range: Set[Range])(implicit
         val nextToken = tokens(nextState.depth)
         if (RightParenOrBracket(nextToken.right)) {
           implicit val style: ScalafmtConfig = styleMap.at(nextToken)
-          trackState(nextState, depth, 0)
           val nextSplits = getActiveSplits(nextToken, nextState, maxCost = 0)
-          traverseSameLineZeroCost(nextSplits, nextState, depth)
+          traverseSameLineZeroCost(nextSplits, nextState)
         } else nextState
       }
     case _ => state
@@ -390,4 +370,29 @@ object BestFirstSearch {
   private def useNoOptZones(implicit style: ScalafmtConfig): Boolean =
     style.runner.optimizer.disableOptimizationsInsideSensitiveAreas
 
+  class StateQueue(val nested: Int)(implicit stateOrdering: Ordering[State]) {
+    private def newGeneration = new mutable.PriorityQueue[State]()
+    var generation: mutable.PriorityQueue[State] = newGeneration
+    var generations: List[mutable.PriorityQueue[State]] = Nil
+
+    def addGeneration(): Unit = if (generation.nonEmpty) {
+      generations = generation :: generations
+      generation = newGeneration
+    }
+
+    def dequeue(): State = generation.dequeue()
+    def enqueue(state: State): Unit = generation.enqueue(state)
+    def length: Int = generation.length
+    @tailrec
+    final def isEmpty(): Boolean = generation.isEmpty && {
+      generations match {
+        case head :: tail =>
+          generation = head
+          generations = tail
+          isEmpty()
+        case _ => true
+      }
+    }
+  }
+
 }