layout/generic/nsLineBox.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* representation of one line within a block frame, a CSS line box */

#ifndef nsLineBox_h___
#define nsLineBox_h___

#include "mozilla/Attributes.h"
#include "mozilla/Likely.h"

#include "nsILineIterator.h"
#include "nsIFrame.h"
#include "nsTHashSet.h"

#include <algorithm>

class nsLineBox;
class nsFloatCache;
class nsFloatCacheList;
class nsFloatCacheFreeList;
class nsWindowSizes;

namespace mozilla {
class PresShell;
}  // namespace mozilla

// State cached after reflowing a float. This state is used during
// incremental reflow when we avoid reflowing a float.
class nsFloatCache {
 public:
  nsFloatCache();
#ifdef NS_BUILD_REFCNT_LOGGING
  ~nsFloatCache();
#else
  ~nsFloatCache() = default;
#endif

  nsFloatCache* Next() const { return mNext; }

  nsIFrame* mFloat;  // floating frame

 protected:
  nsFloatCache* mNext;

  friend class nsFloatCacheList;
  friend class nsFloatCacheFreeList;
};

//----------------------------------------

class nsFloatCacheList {
 public:
#ifdef NS_BUILD_REFCNT_LOGGING
  nsFloatCacheList();
#else
  nsFloatCacheList() : mHead(nullptr) {}
#endif
  ~nsFloatCacheList();

  bool IsEmpty() const { return nullptr == mHead; }

  bool NotEmpty() const { return nullptr != mHead; }

  nsFloatCache* Head() const { return mHead; }

  nsFloatCache* Tail() const;

  void DeleteAll();

  nsFloatCache* Find(nsIFrame* aOutOfFlowFrame);

  // Remove a nsFloatCache from this list.  Deleting this nsFloatCache
  // becomes the caller's responsibility.
  void Remove(nsFloatCache* aElement) { RemoveAndReturnPrev(aElement); }

  // Steal away aList's nsFloatCache objects and put them in this
  // list.  aList must not be empty.
  void Append(nsFloatCacheFreeList& aList);

 protected:
  nsFloatCache* mHead;

  // Remove a nsFloatCache from this list.  Deleting this nsFloatCache
  // becomes the caller's responsibility. Returns the nsFloatCache that was
  // before aElement, or nullptr if aElement was the first.
  nsFloatCache* RemoveAndReturnPrev(nsFloatCache* aElement);

  friend class nsFloatCacheFreeList;
};

//---------------------------------------
// Like nsFloatCacheList, but with fast access to the tail

class nsFloatCacheFreeList : private nsFloatCacheList {
 public:
#ifdef NS_BUILD_REFCNT_LOGGING
  nsFloatCacheFreeList();
  ~nsFloatCacheFreeList();
#else
  nsFloatCacheFreeList() : mTail(nullptr) {}
  ~nsFloatCacheFreeList() = default;
#endif

  // Reimplement trivial functions
  bool IsEmpty() const { return nullptr == mHead; }

  nsFloatCache* Head() const { return mHead; }

  nsFloatCache* Tail() const { return mTail; }

  bool NotEmpty() const { return nullptr != mHead; }

  void DeleteAll();

  // Steal away aList's nsFloatCache objects and put them on this
  // free-list.  aList must not be empty.
  void Append(nsFloatCacheList& aList);

  void Append(nsFloatCache* aFloatCache);

  void Remove(nsFloatCache* aElement);

  // Remove an nsFloatCache object from this list and return it, or create
  // a new one if this one is empty; Set its mFloat to aFloat.
  nsFloatCache* Alloc(nsIFrame* aFloat);

 protected:
  nsFloatCache* mTail;

  friend class nsFloatCacheList;
};

//----------------------------------------------------------------------

#define LINE_MAX_CHILD_COUNT INT32_MAX

/**
 * Function to create a line box and initialize it with a single frame.
 * The allocation is infallible.
 * If the frame was moved from another line then you're responsible
 * for notifying that line using NoteFrameRemoved().  Alternatively,
 * it's better to use the next function that does that for you in an
 * optimal way.
 */
nsLineBox* NS_NewLineBox(mozilla::PresShell* aPresShell, nsIFrame* aFrame,
                         bool aIsBlock);
/**
 * Function to create a line box and initialize it with aCount frames
 * that are currently on aFromLine.  The allocation is infallible.
 */
nsLineBox* NS_NewLineBox(mozilla::PresShell* aPresShell, nsLineBox* aFromLine,
                         nsIFrame* aFrame, int32_t aCount);

class nsLineList;

// don't use the following names outside of this file.  Instead, use
// nsLineList::iterator, etc.  These are just here to allow them to
// be specified as parameters to methods of nsLineBox.
class nsLineList_iterator;
class nsLineList_const_iterator;
class nsLineList_reverse_iterator;
class nsLineList_const_reverse_iterator;

/**
 * Users must have the class that is to be part of the list inherit
 * from nsLineLink.  If they want to be efficient, it should be the
 * first base class.  (This was originally nsCLink in a templatized
 * nsCList, but it's still useful separately.)
 */

class nsLineLink {
 public:
  friend class nsLineList;
  friend class nsLineList_iterator;
  friend class nsLineList_reverse_iterator;
  friend class nsLineList_const_iterator;
  friend class nsLineList_const_reverse_iterator;

 private:
  nsLineLink* _mNext;  // or head
  nsLineLink* _mPrev;  // or tail
};

/**
 * The nsLineBox class represents a horizontal line of frames. It contains
 * enough state to support incremental reflow of the frames, event handling
 * for the frames, and rendering of the frames.
 */
class nsLineBox final : public nsLineLink {
 private:
  nsLineBox(nsIFrame* aFrame, int32_t aCount, bool aIsBlock);
  ~nsLineBox();

  // Infallible overloaded new operator. Uses an arena (which comes from the
  // presShell) to perform the allocation.
  void* operator new(size_t sz, mozilla::PresShell* aPresShell);
  void operator delete(void* aPtr, size_t sz) = delete;

 public:
  // Use these functions to allocate and destroy line boxes
  friend nsLineBox* NS_NewLineBox(mozilla::PresShell* aPresShell,
                                  nsIFrame* aFrame, bool aIsBlock);
  friend nsLineBox* NS_NewLineBox(mozilla::PresShell* aPresShell,
                                  nsLineBox* aFromLine, nsIFrame* aFrame,
                                  int32_t aCount);
  void Destroy(mozilla::PresShell* aPresShell);

  // mBlock bit
  bool IsBlock() const { return mFlags.mBlock; }
  bool IsInline() const { return !mFlags.mBlock; }

  // mDirty bit
  void MarkDirty() { mFlags.mDirty = 1; }
  void ClearDirty() { mFlags.mDirty = 0; }
  bool IsDirty() const { return mFlags.mDirty; }

  // mPreviousMarginDirty bit
  void MarkPreviousMarginDirty() { mFlags.mPreviousMarginDirty = 1; }
  void ClearPreviousMarginDirty() { mFlags.mPreviousMarginDirty = 0; }
  bool IsPreviousMarginDirty() const { return mFlags.mPreviousMarginDirty; }

  // mHasClearance bit
  void SetHasClearance() { mFlags.mHasClearance = 1; }
  void ClearHasClearance() { mFlags.mHasClearance = 0; }
  bool HasClearance() const { return mFlags.mHasClearance; }

  // mImpactedByFloat bit
  void SetLineIsImpactedByFloat(bool aValue) {
    mFlags.mImpactedByFloat = aValue;
  }
  bool IsImpactedByFloat() const { return mFlags.mImpactedByFloat; }

  // mLineWrapped bit
  void SetLineWrapped(bool aOn) { mFlags.mLineWrapped = aOn; }
  bool IsLineWrapped() const { return mFlags.mLineWrapped; }

  // mInvalidateTextRuns bit
  void SetInvalidateTextRuns(bool aOn) { mFlags.mInvalidateTextRuns = aOn; }
  bool GetInvalidateTextRuns() const { return mFlags.mInvalidateTextRuns; }

  // mResizeReflowOptimizationDisabled bit
  void DisableResizeReflowOptimization() {
    mFlags.mResizeReflowOptimizationDisabled = true;
  }
  void EnableResizeReflowOptimization() {
    mFlags.mResizeReflowOptimizationDisabled = false;
  }
  bool ResizeReflowOptimizationDisabled() const {
    return mFlags.mResizeReflowOptimizationDisabled;
  }

  // mHasMarker bit
  void SetHasMarker() {
    mFlags.mHasMarker = true;
    InvalidateCachedIsEmpty();
  }
  void ClearHasMarker() {
    mFlags.mHasMarker = false;
    InvalidateCachedIsEmpty();
  }
  bool HasMarker() const { return mFlags.mHasMarker; }

  // mHadFloatPushed bit
  void SetHadFloatPushed() { mFlags.mHadFloatPushed = true; }
  void ClearHadFloatPushed() { mFlags.mHadFloatPushed = false; }
  bool HadFloatPushed() const { return mFlags.mHadFloatPushed; }

  // mHasLineClampEllipsis bit
  void SetHasLineClampEllipsis() { mFlags.mHasLineClampEllipsis = true; }
  void ClearHasLineClampEllipsis() { mFlags.mHasLineClampEllipsis = false; }
  bool HasLineClampEllipsis() const { return mFlags.mHasLineClampEllipsis; }

  // mMovedFragments bit
  void SetMovedFragments() { mFlags.mMovedFragments = true; }
  void ClearMovedFragments() { mFlags.mMovedFragments = false; }
  bool MovedFragments() const { return mFlags.mMovedFragments; }

 private:
  // Add a hash table for fast lookup when the line has more frames than this.
  static const uint32_t kMinChildCountForHashtable = 200;

  /**
   * Take ownership of aFromLine's hash table and remove the frames that
   * stay on aFromLine from it, i.e. aFromLineNewCount frames starting with
   * mFirstChild.  This method is used to optimize moving a large number
   * of frames from one line to the next.
   */
  void StealHashTableFrom(nsLineBox* aFromLine, uint32_t aFromLineNewCount);

  /**
   * Does the equivalent of this->NoteFrameAdded and aFromLine->NoteFrameRemoved
   * for each frame on this line, but in a optimized way.
   */
  void NoteFramesMovedFrom(nsLineBox* aFromLine);

  void SwitchToHashtable() {
    MOZ_ASSERT(!mFlags.mHasHashedFrames);
    uint32_t count = GetChildCount();
    mFlags.mHasHashedFrames = 1;
    uint32_t minLength =
        std::max(kMinChildCountForHashtable,
                 uint32_t(PLDHashTable::kDefaultInitialLength));
    mFrames = new nsTHashSet<nsIFrame*>(std::max(count, minLength));
    for (nsIFrame* f = mFirstChild; count-- > 0; f = f->GetNextSibling()) {
      mFrames->Insert(f);
    }
  }
  void SwitchToCounter() {
    MOZ_ASSERT(mFlags.mHasHashedFrames);
    uint32_t count = GetChildCount();
    delete mFrames;
    mFlags.mHasHashedFrames = 0;
    mChildCount = count;
  }

 public:
  int32_t GetChildCount() const {
    return MOZ_UNLIKELY(mFlags.mHasHashedFrames) ? mFrames->Count()
                                                 : mChildCount;
  }

  /**
   * Register that aFrame is now on this line.
   */
  void NoteFrameAdded(nsIFrame* aFrame) {
    if (MOZ_UNLIKELY(mFlags.mHasHashedFrames)) {
      mFrames->Insert(aFrame);
    } else {
      if (++mChildCount >= kMinChildCountForHashtable) {
        SwitchToHashtable();
      }
    }
  }

  /**
   * Register that aFrame is not on this line anymore.
   */
  void NoteFrameRemoved(nsIFrame* aFrame) {
    MOZ_ASSERT(GetChildCount() > 0);
    if (MOZ_UNLIKELY(mFlags.mHasHashedFrames)) {
      mFrames->Remove(aFrame);
      if (mFrames->Count() < kMinChildCountForHashtable) {
        SwitchToCounter();
      }
    } else {
      --mChildCount;
    }
  }

  // mBreakType value
  // Break information is applied *before* the line if the line is a block,
  // or *after* the line if the line is an inline. Confusing, I know, but
  // using different names should help.
  using StyleClear = mozilla::StyleClear;
  bool HasBreakBefore() const {
    return IsBlock() && StyleClear::None != BreakType();
  }
  void SetBreakTypeBefore(StyleClear aBreakType) {
    MOZ_ASSERT(IsBlock(), "Only blocks have break-before");
    MOZ_ASSERT(
        aBreakType == StyleClear::None || aBreakType == StyleClear::Left ||
            aBreakType == StyleClear::Right || aBreakType == StyleClear::Both,
        "Only float break types are allowed before a line");
    mFlags.mBreakType = aBreakType;
  }
  StyleClear GetBreakTypeBefore() const {
    return IsBlock() ? BreakType() : StyleClear::None;
  }

  bool HasBreakAfter() const {
    return !IsBlock() && StyleClear::None != BreakType();
  }
  void SetBreakTypeAfter(StyleClear aBreakType) {
    MOZ_ASSERT(!IsBlock(), "Only inlines have break-after");
    mFlags.mBreakType = aBreakType;
  }
  bool HasFloatBreakAfter() const {
    return !IsBlock() && (StyleClear::Left == BreakType() ||
                          StyleClear::Right == BreakType() ||
                          StyleClear::Both == BreakType());
  }
  StyleClear GetBreakTypeAfter() const {
    return !IsBlock() ? BreakType() : StyleClear::None;
  }

  // mCarriedOutBEndMargin value
  nsCollapsingMargin GetCarriedOutBEndMargin() const;
  // Returns true if the margin changed
  bool SetCarriedOutBEndMargin(nsCollapsingMargin aValue);

  // mFloats
  bool HasFloats() const {
    return (IsInline() && mInlineData) && mInlineData->mFloats.NotEmpty();
  }
  nsFloatCache* GetFirstFloat();
  void FreeFloats(nsFloatCacheFreeList& aFreeList);
  void AppendFloats(nsFloatCacheFreeList& aFreeList);
  bool RemoveFloat(nsIFrame* aFrame);

  // The ink overflow area should never be used for things that affect layout.
  // The scrollable overflow area are permitted to affect layout for handling of
  // overflow and scrollbars.
  void SetOverflowAreas(const mozilla::OverflowAreas& aOverflowAreas);
  mozilla::LogicalRect GetOverflowArea(mozilla::OverflowType aType,
                                       mozilla::WritingMode aWM,
                                       const nsSize& aContainerSize) {
    return mozilla::LogicalRect(aWM, GetOverflowArea(aType), aContainerSize);
  }
  nsRect GetOverflowArea(mozilla::OverflowType aType) const {
    return mData ? mData->mOverflowAreas.Overflow(aType) : GetPhysicalBounds();
  }
  mozilla::OverflowAreas GetOverflowAreas() const {
    if (mData) {
      return mData->mOverflowAreas;
    }
    nsRect bounds = GetPhysicalBounds();
    return mozilla::OverflowAreas(bounds, bounds);
  }
  nsRect InkOverflowRect() const {
    return GetOverflowArea(mozilla::OverflowType::Ink);
  }
  nsRect ScrollableOverflowRect() {
    return GetOverflowArea(mozilla::OverflowType::Scrollable);
  }

  void SlideBy(nscoord aDBCoord, const nsSize& aContainerSize) {
    NS_ASSERTION(
        aContainerSize == mContainerSize || mContainerSize == nsSize(-1, -1),
        "container size doesn't match");
    mContainerSize = aContainerSize;
    mBounds.BStart(mWritingMode) += aDBCoord;
    if (mData) {
      // Use a null containerSize to convert vector from logical to physical.
      const nsSize nullContainerSize;
      nsPoint physicalDelta =
          mozilla::LogicalPoint(mWritingMode, 0, aDBCoord)
              .GetPhysicalPoint(mWritingMode, nullContainerSize);
      for (const auto otype : mozilla::AllOverflowTypes()) {
        mData->mOverflowAreas.Overflow(otype) += physicalDelta;
      }
    }
  }

  // Container-size for the line is changing (and therefore if writing mode
  // was vertical-rl, the line will move physically; this is like SlideBy,
  // but it is the container size instead of the line's own logical coord
  // that is changing.
  nsSize UpdateContainerSize(const nsSize aNewContainerSize) {
    NS_ASSERTION(mContainerSize != nsSize(-1, -1), "container size not set");
    nsSize delta = mContainerSize - aNewContainerSize;
    mContainerSize = aNewContainerSize;
    // this has a physical-coordinate effect only in vertical-rl mode
    if (mWritingMode.IsVerticalRL() && mData) {
      nsPoint physicalDelta(-delta.width, 0);
      for (const auto otype : mozilla::AllOverflowTypes()) {
        mData->mOverflowAreas.Overflow(otype) += physicalDelta;
      }
    }
    return delta;
  }

  void IndentBy(nscoord aDICoord, const nsSize& aContainerSize) {
    NS_ASSERTION(
        aContainerSize == mContainerSize || mContainerSize == nsSize(-1, -1),
        "container size doesn't match");
    mContainerSize = aContainerSize;
    mBounds.IStart(mWritingMode) += aDICoord;
  }

  void ExpandBy(nscoord aDISize, const nsSize& aContainerSize) {
    NS_ASSERTION(
        aContainerSize == mContainerSize || mContainerSize == nsSize(-1, -1),
        "container size doesn't match");
    mContainerSize = aContainerSize;
    mBounds.ISize(mWritingMode) += aDISize;
  }

  /**
   * The logical ascent (distance from block-start to baseline) of the
   * linebox is the logical ascent of the anonymous inline box (for
   * which we don't actually create a frame) that wraps all the
   * consecutive inline children of a block.
   *
   * This is currently unused for block lines.
   */
  nscoord GetLogicalAscent() const { return mAscent; }
  void SetLogicalAscent(nscoord aAscent) { mAscent = aAscent; }

  nscoord BStart() const { return mBounds.BStart(mWritingMode); }
  nscoord BSize() const { return mBounds.BSize(mWritingMode); }
  nscoord BEnd() const { return mBounds.BEnd(mWritingMode); }
  nscoord IStart() const { return mBounds.IStart(mWritingMode); }
  nscoord ISize() const { return mBounds.ISize(mWritingMode); }
  nscoord IEnd() const { return mBounds.IEnd(mWritingMode); }
  void SetBoundsEmpty() {
    mBounds.IStart(mWritingMode) = 0;
    mBounds.ISize(mWritingMode) = 0;
    mBounds.BStart(mWritingMode) = 0;
    mBounds.BSize(mWritingMode) = 0;
  }

  using PostDestroyData = nsIFrame::PostDestroyData;
  static void DeleteLineList(nsPresContext* aPresContext, nsLineList& aLines,
                             nsIFrame* aDestructRoot, nsFrameList* aFrames,
                             PostDestroyData& aPostDestroyData);

  // search from end to beginning of [aBegin, aEnd)
  // Returns true if it found the line and false if not.
  // Moves aEnd as it searches so that aEnd points to the resulting line.
  // aLastFrameBeforeEnd is the last frame before aEnd (so if aEnd is
  // the end of the line list, it's just the last frame in the frame
  // list).
  static bool RFindLineContaining(nsIFrame* aFrame,
                                  const nsLineList_iterator& aBegin,
                                  nsLineList_iterator& aEnd,
                                  nsIFrame* aLastFrameBeforeEnd,
                                  int32_t* aFrameIndexInLine);

#ifdef DEBUG_FRAME_DUMP
  static const char* BreakTypeToString(StyleClear aBreakType);
  char* StateToString(char* aBuf, int32_t aBufSize) const;

  void List(FILE* out, int32_t aIndent,
            nsIFrame::ListFlags aFlags = nsIFrame::ListFlags()) const;
  void List(FILE* out = stderr, const char* aPrefix = "",
            nsIFrame::ListFlags aFlags = nsIFrame::ListFlags()) const;
  nsIFrame* LastChild() const;
#endif

  void AddSizeOfExcludingThis(nsWindowSizes& aSizes) const;

  // Find the index of aFrame within the line, starting search at the start.
  int32_t IndexOf(nsIFrame* aFrame) const;

  // Find the index of aFrame within the line, starting search at the end.
  // (Produces the same result as IndexOf, but with different performance
  // characteristics.)  The caller must provide the last frame in the line.
  int32_t RIndexOf(nsIFrame* aFrame, nsIFrame* aLastFrameInLine) const;

  bool Contains(nsIFrame* aFrame) const {
    return MOZ_UNLIKELY(mFlags.mHasHashedFrames) ? mFrames->Contains(aFrame)
                                                 : IndexOf(aFrame) >= 0;
  }

  // whether the line box is "logically" empty (just like nsIFrame::IsEmpty)
  bool IsEmpty() const;

  // Call this only while in Reflow() for the block the line belongs
  // to, only between reflowing the line (or sliding it, if we skip
  // reflowing it) and the end of reflowing the block.
  bool CachedIsEmpty();

  void InvalidateCachedIsEmpty() { mFlags.mEmptyCacheValid = false; }

  // For debugging purposes
  bool IsValidCachedIsEmpty() { return mFlags.mEmptyCacheValid; }

#ifdef DEBUG
  static int32_t GetCtorCount();
#endif

  nsIFrame* mFirstChild;

  mozilla::WritingMode mWritingMode;

  // Physical size. Use only for physical <-> logical coordinate conversion.
  nsSize mContainerSize;

 private:
  mozilla::LogicalRect mBounds;

 public:
  const mozilla::LogicalRect& GetBounds() { return mBounds; }
  nsRect GetPhysicalBounds() const {
    if (mBounds.IsAllZero()) {
      return nsRect(0, 0, 0, 0);
    }

    NS_ASSERTION(mContainerSize != nsSize(-1, -1),
                 "mContainerSize not initialized");
    return mBounds.GetPhysicalRect(mWritingMode, mContainerSize);
  }
  void SetBounds(mozilla::WritingMode aWritingMode, nscoord aIStart,
                 nscoord aBStart, nscoord aISize, nscoord aBSize,
                 const nsSize& aContainerSize) {
    mWritingMode = aWritingMode;
    mContainerSize = aContainerSize;
    mBounds =
        mozilla::LogicalRect(aWritingMode, aIStart, aBStart, aISize, aBSize);
  }

  // mFlags.mHasHashedFrames says which one to use
  union {
    nsTHashSet<nsIFrame*>* mFrames;
    uint32_t mChildCount;
  };

  struct FlagBits {
    bool mDirty : 1;
    bool mPreviousMarginDirty : 1;
    bool mHasClearance : 1;
    bool mBlock : 1;
    bool mImpactedByFloat : 1;
    bool mLineWrapped : 1;
    bool mInvalidateTextRuns : 1;
    // default 0 = means that the opt potentially applies to this line.
    // 1 = never skip reflowing this line for a resize reflow
    bool mResizeReflowOptimizationDisabled : 1;
    bool mEmptyCacheValid : 1;
    bool mEmptyCacheState : 1;
    // mHasMarker indicates that this is an inline line whose block's
    // ::marker is adjacent to this line and non-empty.
    bool mHasMarker : 1;
    // Indicates that this line *may* have a placeholder for a float
    // that was pushed to a later column or page.
    bool mHadFloatPushed : 1;
    bool mHasHashedFrames : 1;
    // Indicates that this line is the one identified by an ancestor block
    // with -webkit-line-clamp on its legacy flex container, and that subsequent
    // lines under that block are "clamped" away, and therefore we need to
    // render a 'text-overflow: ellipsis'-like marker in this line.  At most one
    // line in the set of lines found by LineClampLineIterator for a given
    // block will have this flag set.
    bool mHasLineClampEllipsis : 1;
    // Has this line moved to a different fragment of the block since
    // the last time it was reflowed?
    bool mMovedFragments : 1;
    StyleClear mBreakType;
  };

  struct ExtraData {
    explicit ExtraData(const nsRect& aBounds)
        : mOverflowAreas(aBounds, aBounds) {}
    mozilla::OverflowAreas mOverflowAreas;
  };

  struct ExtraBlockData : public ExtraData {
    explicit ExtraBlockData(const nsRect& aBounds)
        : ExtraData(aBounds), mCarriedOutBEndMargin() {}
    nsCollapsingMargin mCarriedOutBEndMargin;
  };

  struct ExtraInlineData : public ExtraData {
    explicit ExtraInlineData(const nsRect& aBounds)
        : ExtraData(aBounds),
          mFloatEdgeIStart(nscoord_MIN),
          mFloatEdgeIEnd(nscoord_MIN) {}
    nscoord mFloatEdgeIStart;
    nscoord mFloatEdgeIEnd;
    nsFloatCacheList mFloats;
  };

  bool GetFloatEdges(nscoord* aStart, nscoord* aEnd) const {
    MOZ_ASSERT(IsInline(), "block line can't have float edges");
    if (mInlineData && mInlineData->mFloatEdgeIStart != nscoord_MIN) {
      *aStart = mInlineData->mFloatEdgeIStart;
      *aEnd = mInlineData->mFloatEdgeIEnd;
      return true;
    }
    return false;
  }
  void SetFloatEdges(nscoord aStart, nscoord aEnd);
  void ClearFloatEdges();

 protected:
  nscoord mAscent;  // see |SetAscent| / |GetAscent|
  static_assert(sizeof(FlagBits) <= sizeof(uint32_t),
                "size of FlagBits should not be larger than size of uint32_t");
  union {
    uint32_t mAllFlags;
    FlagBits mFlags;
  };

  StyleClear BreakType() const { return mFlags.mBreakType; };

  union {
    ExtraData* mData;
    ExtraBlockData* mBlockData;
    ExtraInlineData* mInlineData;
  };

  void Cleanup();
  void MaybeFreeData();
};

/**
 * A linked list type where the items in the list must inherit from
 * a link type to fuse allocations.
 *
 * API heavily based on the |list| class in the C++ standard.
 */

class nsLineList_iterator {
 public:
  friend class nsLineList;
  friend class nsLineList_reverse_iterator;
  friend class nsLineList_const_iterator;
  friend class nsLineList_const_reverse_iterator;

  typedef nsLineList_iterator iterator_self_type;
  typedef nsLineList_reverse_iterator iterator_reverse_type;

  typedef nsLineBox& reference;
  typedef const nsLineBox& const_reference;

  typedef nsLineBox* pointer;
  typedef const nsLineBox* const_pointer;

  typedef uint32_t size_type;
  typedef int32_t difference_type;

  typedef nsLineLink link_type;

#ifdef DEBUG
  nsLineList_iterator() : mListLink(nullptr) {
    memset(&mCurrent, 0xcd, sizeof(mCurrent));
  }
#else
  // Auto generated default constructor OK.
#endif
  // Auto generated copy-constructor OK.

  inline iterator_self_type& operator=(const iterator_self_type& aOther);
  inline iterator_self_type& operator=(const iterator_reverse_type& aOther);

  iterator_self_type& operator++() {
    mCurrent = mCurrent->_mNext;
    return *this;
  }

  iterator_self_type operator++(int) {
    iterator_self_type rv(*this);
    mCurrent = mCurrent->_mNext;
    return rv;
  }

  iterator_self_type& operator--() {
    mCurrent = mCurrent->_mPrev;
    return *this;
  }

  iterator_self_type operator--(int) {
    iterator_self_type rv(*this);
    mCurrent = mCurrent->_mPrev;
    return rv;
  }

  reference operator*() {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return *static_cast<pointer>(mCurrent);
  }

  pointer operator->() {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<pointer>(mCurrent);
  }

  pointer get() {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<pointer>(mCurrent);
  }

  operator pointer() {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<pointer>(mCurrent);
  }

  const_reference operator*() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return *static_cast<const_pointer>(mCurrent);
  }

  const_pointer operator->() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }

#ifndef __MWERKS__
  operator const_pointer() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }
#endif /* !__MWERKS__ */

  iterator_self_type next() {
    iterator_self_type copy(*this);
    return ++copy;
  }

  const iterator_self_type next() const {
    iterator_self_type copy(*this);
    return ++copy;
  }

  iterator_self_type prev() {
    iterator_self_type copy(*this);
    return --copy;
  }

  const iterator_self_type prev() const {
    iterator_self_type copy(*this);
    return --copy;
  }

  // Passing by value rather than by reference and reference to const
  // to keep AIX happy.
  bool operator==(const iterator_self_type aOther) const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mListLink == aOther.mListLink,
               "comparing iterators over different lists");
    return mCurrent == aOther.mCurrent;
  }
  bool operator!=(const iterator_self_type aOther) const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mListLink == aOther.mListLink,
               "comparing iterators over different lists");
    return mCurrent != aOther.mCurrent;
  }
  bool operator==(const iterator_self_type aOther) {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mListLink == aOther.mListLink,
               "comparing iterators over different lists");
    return mCurrent == aOther.mCurrent;
  }
  bool operator!=(const iterator_self_type aOther) {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mListLink == aOther.mListLink,
               "comparing iterators over different lists");
    return mCurrent != aOther.mCurrent;
  }

#ifdef DEBUG
  bool IsInSameList(const iterator_self_type aOther) const {
    return mListLink == aOther.mListLink;
  }
#endif

 private:
  link_type* mCurrent;
#ifdef DEBUG
  link_type* mListLink;  // the list's link, i.e., the end
#endif
};

class nsLineList_reverse_iterator {
 public:
  friend class nsLineList;
  friend class nsLineList_iterator;
  friend class nsLineList_const_iterator;
  friend class nsLineList_const_reverse_iterator;

  typedef nsLineList_reverse_iterator iterator_self_type;
  typedef nsLineList_iterator iterator_reverse_type;

  typedef nsLineBox& reference;
  typedef const nsLineBox& const_reference;

  typedef nsLineBox* pointer;
  typedef const nsLineBox* const_pointer;

  typedef uint32_t size_type;
  typedef int32_t difference_type;

  typedef nsLineLink link_type;

#ifdef DEBUG
  nsLineList_reverse_iterator() : mListLink(nullptr) {
    memset(&mCurrent, 0xcd, sizeof(mCurrent));
  }
#else
  // Auto generated default constructor OK.
#endif
  // Auto generated copy-constructor OK.

  inline iterator_self_type& operator=(const iterator_reverse_type& aOther);
  inline iterator_self_type& operator=(const iterator_self_type& aOther);

  iterator_self_type& operator++() {
    mCurrent = mCurrent->_mPrev;
    return *this;
  }

  iterator_self_type operator++(int) {
    iterator_self_type rv(*this);
    mCurrent = mCurrent->_mPrev;
    return rv;
  }

  iterator_self_type& operator--() {
    mCurrent = mCurrent->_mNext;
    return *this;
  }

  iterator_self_type operator--(int) {
    iterator_self_type rv(*this);
    mCurrent = mCurrent->_mNext;
    return rv;
  }

  reference operator*() {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return *static_cast<pointer>(mCurrent);
  }

  pointer operator->() {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<pointer>(mCurrent);
  }

  pointer get() {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<pointer>(mCurrent);
  }

  operator pointer() {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<pointer>(mCurrent);
  }

  const_reference operator*() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return *static_cast<const_pointer>(mCurrent);
  }

  const_pointer operator->() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }

#ifndef __MWERKS__
  operator const_pointer() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }
#endif /* !__MWERKS__ */

  // Passing by value rather than by reference and reference to const
  // to keep AIX happy.
  bool operator==(const iterator_self_type aOther) const {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent == aOther.mCurrent;
  }
  bool operator!=(const iterator_self_type aOther) const {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent != aOther.mCurrent;
  }
  bool operator==(const iterator_self_type aOther) {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent == aOther.mCurrent;
  }
  bool operator!=(const iterator_self_type aOther) {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent != aOther.mCurrent;
  }

#ifdef DEBUG
  bool IsInSameList(const iterator_self_type aOther) const {
    return mListLink == aOther.mListLink;
  }
#endif

 private:
  link_type* mCurrent;
#ifdef DEBUG
  link_type* mListLink;  // the list's link, i.e., the end
#endif
};

class nsLineList_const_iterator {
 public:
  friend class nsLineList;
  friend class nsLineList_iterator;
  friend class nsLineList_reverse_iterator;
  friend class nsLineList_const_reverse_iterator;

  typedef nsLineList_const_iterator iterator_self_type;
  typedef nsLineList_const_reverse_iterator iterator_reverse_type;
  typedef nsLineList_iterator iterator_nonconst_type;
  typedef nsLineList_reverse_iterator iterator_nonconst_reverse_type;

  typedef nsLineBox& reference;
  typedef const nsLineBox& const_reference;

  typedef nsLineBox* pointer;
  typedef const nsLineBox* const_pointer;

  typedef uint32_t size_type;
  typedef int32_t difference_type;

  typedef nsLineLink link_type;

#ifdef DEBUG
  nsLineList_const_iterator() : mListLink(nullptr) {
    memset(&mCurrent, 0xcd, sizeof(mCurrent));
  }
#else
  // Auto generated default constructor OK.
#endif
  // Auto generated copy-constructor OK.

  inline iterator_self_type& operator=(const iterator_nonconst_type& aOther);
  inline iterator_self_type& operator=(
      const iterator_nonconst_reverse_type& aOther);
  inline iterator_self_type& operator=(const iterator_self_type& aOther);
  inline iterator_self_type& operator=(const iterator_reverse_type& aOther);

  iterator_self_type& operator++() {
    mCurrent = mCurrent->_mNext;
    return *this;
  }

  iterator_self_type operator++(int) {
    iterator_self_type rv(*this);
    mCurrent = mCurrent->_mNext;
    return rv;
  }

  iterator_self_type& operator--() {
    mCurrent = mCurrent->_mPrev;
    return *this;
  }

  iterator_self_type operator--(int) {
    iterator_self_type rv(*this);
    mCurrent = mCurrent->_mPrev;
    return rv;
  }

  const_reference operator*() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return *static_cast<const_pointer>(mCurrent);
  }

  const_pointer operator->() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }

  const_pointer get() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }

#ifndef __MWERKS__
  operator const_pointer() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }
#endif /* !__MWERKS__ */

  const iterator_self_type next() const {
    iterator_self_type copy(*this);
    return ++copy;
  }

  const iterator_self_type prev() const {
    iterator_self_type copy(*this);
    return --copy;
  }

  // Passing by value rather than by reference and reference to const
  // to keep AIX happy.
  bool operator==(const iterator_self_type aOther) const {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent == aOther.mCurrent;
  }
  bool operator!=(const iterator_self_type aOther) const {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent != aOther.mCurrent;
  }
  bool operator==(const iterator_self_type aOther) {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent == aOther.mCurrent;
  }
  bool operator!=(const iterator_self_type aOther) {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent != aOther.mCurrent;
  }

#ifdef DEBUG
  bool IsInSameList(const iterator_self_type aOther) const {
    return mListLink == aOther.mListLink;
  }
#endif

 private:
  const link_type* mCurrent;
#ifdef DEBUG
  const link_type* mListLink;  // the list's link, i.e., the end
#endif
};

class nsLineList_const_reverse_iterator {
 public:
  friend class nsLineList;
  friend class nsLineList_iterator;
  friend class nsLineList_reverse_iterator;
  friend class nsLineList_const_iterator;

  typedef nsLineList_const_reverse_iterator iterator_self_type;
  typedef nsLineList_const_iterator iterator_reverse_type;
  typedef nsLineList_iterator iterator_nonconst_reverse_type;
  typedef nsLineList_reverse_iterator iterator_nonconst_type;

  typedef nsLineBox& reference;
  typedef const nsLineBox& const_reference;

  typedef nsLineBox* pointer;
  typedef const nsLineBox* const_pointer;

  typedef uint32_t size_type;
  typedef int32_t difference_type;

  typedef nsLineLink link_type;

#ifdef DEBUG
  nsLineList_const_reverse_iterator() : mListLink(nullptr) {
    memset(&mCurrent, 0xcd, sizeof(mCurrent));
  }
#else
  // Auto generated default constructor OK.
#endif
  // Auto generated copy-constructor OK.

  inline iterator_self_type& operator=(const iterator_nonconst_type& aOther);
  inline iterator_self_type& operator=(
      const iterator_nonconst_reverse_type& aOther);
  inline iterator_self_type& operator=(const iterator_self_type& aOther);
  inline iterator_self_type& operator=(const iterator_reverse_type& aOther);

  iterator_self_type& operator++() {
    mCurrent = mCurrent->_mPrev;
    return *this;
  }

  iterator_self_type operator++(int) {
    iterator_self_type rv(*this);
    mCurrent = mCurrent->_mPrev;
    return rv;
  }

  iterator_self_type& operator--() {
    mCurrent = mCurrent->_mNext;
    return *this;
  }

  iterator_self_type operator--(int) {
    iterator_self_type rv(*this);
    mCurrent = mCurrent->_mNext;
    return rv;
  }

  const_reference operator*() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return *static_cast<const_pointer>(mCurrent);
  }

  const_pointer operator->() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }

  const_pointer get() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }

#ifndef __MWERKS__
  operator const_pointer() const {
    MOZ_ASSERT(mListLink);
    MOZ_ASSERT(mCurrent != mListLink, "running past end");
    return static_cast<const_pointer>(mCurrent);
  }
#endif /* !__MWERKS__ */

  // Passing by value rather than by reference and reference to const
  // to keep AIX happy.
  bool operator==(const iterator_self_type aOther) const {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent == aOther.mCurrent;
  }
  bool operator!=(const iterator_self_type aOther) const {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent != aOther.mCurrent;
  }
  bool operator==(const iterator_self_type aOther) {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent == aOther.mCurrent;
  }
  bool operator!=(const iterator_self_type aOther) {
    MOZ_ASSERT(mListLink);
    NS_ASSERTION(mListLink == aOther.mListLink,
                 "comparing iterators over different lists");
    return mCurrent != aOther.mCurrent;
  }

#ifdef DEBUG
  bool IsInSameList(const iterator_self_type aOther) const {
    return mListLink == aOther.mListLink;
  }
#endif

  // private:
  const link_type* mCurrent;
#ifdef DEBUG
  const link_type* mListLink;  // the list's link, i.e., the end
#endif
};

class nsLineList {
 public:
  friend class nsLineList_iterator;
  friend class nsLineList_reverse_iterator;
  friend class nsLineList_const_iterator;
  friend class nsLineList_const_reverse_iterator;

  typedef uint32_t size_type;
  typedef int32_t difference_type;

  typedef nsLineLink link_type;

 private:
  link_type mLink;

 public:
  typedef nsLineList self_type;

  typedef nsLineBox& reference;
  typedef const nsLineBox& const_reference;

  typedef nsLineBox* pointer;
  typedef const nsLineBox* const_pointer;

  typedef nsLineList_iterator iterator;
  typedef nsLineList_reverse_iterator reverse_iterator;
  typedef nsLineList_const_iterator const_iterator;
  typedef nsLineList_const_reverse_iterator const_reverse_iterator;

  nsLineList() {
    MOZ_COUNT_CTOR(nsLineList);
    clear();
  }

  MOZ_COUNTED_DTOR(nsLineList)

  const_iterator begin() const {
    const_iterator rv;
    rv.mCurrent = mLink._mNext;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  iterator begin() {
    iterator rv;
    rv.mCurrent = mLink._mNext;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  iterator begin(nsLineBox* aLine) {
    iterator rv;
    rv.mCurrent = aLine;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  const_iterator end() const {
    const_iterator rv;
    rv.mCurrent = &mLink;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  iterator end() {
    iterator rv;
    rv.mCurrent = &mLink;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  const_reverse_iterator rbegin() const {
    const_reverse_iterator rv;
    rv.mCurrent = mLink._mPrev;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  reverse_iterator rbegin() {
    reverse_iterator rv;
    rv.mCurrent = mLink._mPrev;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  reverse_iterator rbegin(nsLineBox* aLine) {
    reverse_iterator rv;
    rv.mCurrent = aLine;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  const_reverse_iterator rend() const {
    const_reverse_iterator rv;
    rv.mCurrent = &mLink;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  reverse_iterator rend() {
    reverse_iterator rv;
    rv.mCurrent = &mLink;
#ifdef DEBUG
    rv.mListLink = &mLink;
#endif
    return rv;
  }

  bool empty() const { return mLink._mNext == &mLink; }

  // NOTE: O(N).
  size_type size() const {
    size_type count = 0;
    for (const link_type* cur = mLink._mNext; cur != &mLink;
         cur = cur->_mNext) {
      ++count;
    }
    return count;
  }

  pointer front() {
    NS_ASSERTION(!empty(), "no element to return");
    return static_cast<pointer>(mLink._mNext);
  }

  const_pointer front() const {
    NS_ASSERTION(!empty(), "no element to return");
    return static_cast<const_pointer>(mLink._mNext);
  }

  pointer back() {
    NS_ASSERTION(!empty(), "no element to return");
    return static_cast<pointer>(mLink._mPrev);
  }

  const_pointer back() const {
    NS_ASSERTION(!empty(), "no element to return");
    return static_cast<const_pointer>(mLink._mPrev);
  }

  void push_front(pointer aNew) {
    aNew->_mNext = mLink._mNext;
    mLink._mNext->_mPrev = aNew;
    aNew->_mPrev = &mLink;
    mLink._mNext = aNew;
  }

  void pop_front()
  // NOTE: leaves dangling next/prev pointers
  {
    NS_ASSERTION(!empty(), "no element to pop");
    link_type* newFirst = mLink._mNext->_mNext;
    newFirst->_mPrev = &mLink;
    // mLink._mNext->_mNext = nullptr;
    // mLink._mNext->_mPrev = nullptr;
    mLink._mNext = newFirst;
  }

  void push_back(pointer aNew) {
    aNew->_mPrev = mLink._mPrev;
    mLink._mPrev->_mNext = aNew;
    aNew->_mNext = &mLink;
    mLink._mPrev = aNew;
  }

  void pop_back()
  // NOTE: leaves dangling next/prev pointers
  {
    NS_ASSERTION(!empty(), "no element to pop");
    link_type* newLast = mLink._mPrev->_mPrev;
    newLast->_mNext = &mLink;
    // mLink._mPrev->_mPrev = nullptr;
    // mLink._mPrev->_mNext = nullptr;
    mLink._mPrev = newLast;
  }

  // inserts x before position
  iterator before_insert(iterator position, pointer x) {
    // use |mCurrent| to prevent DEBUG_PASS_END assertions
    x->_mPrev = position.mCurrent->_mPrev;
    x->_mNext = position.mCurrent;
    position.mCurrent->_mPrev->_mNext = x;
    position.mCurrent->_mPrev = x;
    return --position;
  }

  // inserts x after position
  iterator after_insert(iterator position, pointer x) {
    // use |mCurrent| to prevent DEBUG_PASS_END assertions
    x->_mNext = position.mCurrent->_mNext;
    x->_mPrev = position.mCurrent;
    position.mCurrent->_mNext->_mPrev = x;
    position.mCurrent->_mNext = x;
    return ++position;
  }

  // returns iterator pointing to after the element
  iterator erase(iterator position)
  // NOTE: leaves dangling next/prev pointers
  {
    position->_mPrev->_mNext = position->_mNext;
    position->_mNext->_mPrev = position->_mPrev;
    return ++position;
  }

  void swap(self_type& y) {
    link_type tmp(y.mLink);
    y.mLink = mLink;
    mLink = tmp;

    if (!empty()) {
      mLink._mNext->_mPrev = &mLink;
      mLink._mPrev->_mNext = &mLink;
    }

    if (!y.empty()) {
      y.mLink._mNext->_mPrev = &y.mLink;
      y.mLink._mPrev->_mNext = &y.mLink;
    }
  }

  void clear()
  // NOTE:  leaves dangling next/prev pointers
  {
    mLink._mNext = &mLink;
    mLink._mPrev = &mLink;
  }

  // inserts the conts of x before position and makes x empty
  void splice(iterator position, self_type& x) {
    // use |mCurrent| to prevent DEBUG_PASS_END assertions
    position.mCurrent->_mPrev->_mNext = x.mLink._mNext;
    x.mLink._mNext->_mPrev = position.mCurrent->_mPrev;
    x.mLink._mPrev->_mNext = position.mCurrent;
    position.mCurrent->_mPrev = x.mLink._mPrev;
    x.clear();
  }

  // Inserts element *i from list x before position and removes
  // it from x.
  void splice(iterator position, self_type& x, iterator i) {
    NS_ASSERTION(!x.empty(), "Can't insert from empty list.");
    NS_ASSERTION(position != i && position.mCurrent != i->_mNext,
                 "We don't check for this case.");

    // remove from |x|
    i->_mPrev->_mNext = i->_mNext;
    i->_mNext->_mPrev = i->_mPrev;

    // use |mCurrent| to prevent DEBUG_PASS_END assertions
    // link into |this|, before-side
    i->_mPrev = position.mCurrent->_mPrev;
    position.mCurrent->_mPrev->_mNext = i.get();

    // link into |this|, after-side
    i->_mNext = position.mCurrent;
    position.mCurrent->_mPrev = i.get();
  }

  // Inserts elements in [|first|, |last|), which are in |x|,
  // into |this| before |position| and removes them from |x|.
  void splice(iterator position, self_type& x, iterator first, iterator last) {
    NS_ASSERTION(!x.empty(), "Can't insert from empty list.");

    if (first == last) return;

    --last;  // so we now want to move [first, last]
    // remove from |x|
    first->_mPrev->_mNext = last->_mNext;
    last->_mNext->_mPrev = first->_mPrev;

    // use |mCurrent| to prevent DEBUG_PASS_END assertions
    // link into |this|, before-side
    first->_mPrev = position.mCurrent->_mPrev;
    position.mCurrent->_mPrev->_mNext = first.get();

    // link into |this|, after-side
    last->_mNext = position.mCurrent;
    position.mCurrent->_mPrev = last.get();
  }
};

// Many of these implementations of operator= don't work yet.  I don't
// know why.

#ifdef DEBUG

// NOTE: ASSIGN_FROM is meant to be used *only* as the entire body
// of a function and therefore lacks PR_{BEGIN,END}_MACRO
#  define ASSIGN_FROM(other_)     \
    mCurrent = other_.mCurrent;   \
    mListLink = other_.mListLink; \
    return *this;

#else /* !NS_LINELIST_DEBUG_PASS_END */

#  define ASSIGN_FROM(other_)   \
    mCurrent = other_.mCurrent; \
    return *this;

#endif /* !NS_LINELIST_DEBUG_PASS_END */

inline nsLineList_iterator& nsLineList_iterator::operator=(
    const nsLineList_iterator& aOther) = default;

inline nsLineList_iterator& nsLineList_iterator::operator=(
    const nsLineList_reverse_iterator& aOther) {
  ASSIGN_FROM(aOther)
}

inline nsLineList_reverse_iterator& nsLineList_reverse_iterator::operator=(
    const nsLineList_iterator& aOther) {
  ASSIGN_FROM(aOther)
}

inline nsLineList_reverse_iterator& nsLineList_reverse_iterator::operator=(
    const nsLineList_reverse_iterator& aOther) = default;

inline nsLineList_const_iterator& nsLineList_const_iterator::operator=(
    const nsLineList_iterator& aOther) {
  ASSIGN_FROM(aOther)
}

inline nsLineList_const_iterator& nsLineList_const_iterator::operator=(
    const nsLineList_reverse_iterator& aOther) {
  ASSIGN_FROM(aOther)
}

inline nsLineList_const_iterator& nsLineList_const_iterator::operator=(
    const nsLineList_const_iterator& aOther) = default;

inline nsLineList_const_iterator& nsLineList_const_iterator::operator=(
    const nsLineList_const_reverse_iterator& aOther) {
  ASSIGN_FROM(aOther)
}

inline nsLineList_const_reverse_iterator&
nsLineList_const_reverse_iterator::operator=(
    const nsLineList_iterator& aOther) {
  ASSIGN_FROM(aOther)
}

inline nsLineList_const_reverse_iterator&
nsLineList_const_reverse_iterator::operator=(
    const nsLineList_reverse_iterator& aOther) {
  ASSIGN_FROM(aOther)
}

inline nsLineList_const_reverse_iterator&
nsLineList_const_reverse_iterator::operator=(
    const nsLineList_const_iterator& aOther) {
  ASSIGN_FROM(aOther)
}

inline nsLineList_const_reverse_iterator&
nsLineList_const_reverse_iterator::operator=(
    const nsLineList_const_reverse_iterator& aOther) = default;

//----------------------------------------------------------------------

class nsLineIterator final : public nsILineIterator {
 public:
  nsLineIterator();
  ~nsLineIterator();

  virtual void DisposeLineIterator() override;

  virtual int32_t GetNumLines() const override;
  virtual bool GetDirection() override;

  mozilla::Result<LineInfo, nsresult> GetLine(
      int32_t aLineNumber) const override;
  virtual int32_t FindLineContaining(nsIFrame* aFrame,
                                     int32_t aStartLine = 0) override;
  NS_IMETHOD FindFrameAt(int32_t aLineNumber, nsPoint aPos,
                         nsIFrame** aFrameFound, bool* aPosIsBeforeFirstFrame,
                         bool* aPosIsAfterLastFrame) const override;

  NS_IMETHOD GetNextSiblingOnLine(nsIFrame*& aFrame,
                                  int32_t aLineNumber) const override;
  NS_IMETHOD CheckLineOrder(int32_t aLine, bool* aIsReordered,
                            nsIFrame** aFirstVisual,
                            nsIFrame** aLastVisual) override;
  nsresult Init(nsLineList& aLines, bool aRightToLeft);

 private:
  nsLineBox* PrevLine() {
    if (0 == mIndex) {
      return nullptr;
    }
    return mLines[--mIndex];
  }

  nsLineBox* NextLine() {
    if (mIndex >= mNumLines - 1) {
      return nullptr;
    }
    return mLines[++mIndex];
  }

  nsLineBox* LineAt(int32_t aIndex) {
    if ((aIndex < 0) || (aIndex >= mNumLines)) {
      return nullptr;
    }
    return mLines[aIndex];
  }

  nsLineBox** mLines;
  int32_t mIndex;
  int32_t mNumLines;
  bool mRightToLeft;
};

#endif /* nsLineBox_h___ */