Source code

Revision control

Copy as Markdown

Other Tools

/* -*- 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 */
* Implementation of
* form. This can and should be used to avoid recursion on the stack and lots
* of function calls during shadow-including tree iteration.
#ifndef mozilla_dom_ShadowIncludingTreeIterator_h
#define mozilla_dom_ShadowIncludingTreeIterator_h
#include "nsINode.h"
#include "nsTArray.h"
#include "mozilla/dom/Element.h"
#include "mozilla/dom/ShadowRoot.h"
namespace mozilla::dom {
class ShadowIncludingTreeIterator {
* Initialize an iterator with aRoot. After that it can be iterated with a
* range-based for loop. At the moment, that's the only supported form of use
* for this iterator.
explicit ShadowIncludingTreeIterator(nsINode& aRoot) : mCurrent(&aRoot) {
#ifdef DEBUG
~ShadowIncludingTreeIterator() {
"Don't mutate the DOM while using a ShadowIncludingTreeIterator");
#endif // DEBUG
// Basic support for range-based for loops. This will modify the iterator as
// it goes.
ShadowIncludingTreeIterator& begin() { return *this; }
std::nullptr_t end() const { return nullptr; }
bool operator!=(std::nullptr_t) const { return !!mCurrent; }
explicit operator bool() const { return !!mCurrent; }
void operator++() { Next(); }
void SkipChildren() {
MOZ_ASSERT(mCurrent, "Shouldn't be at end");
mCurrent = mCurrent->GetNextNonChildNode(mRoots.LastElement());
nsINode* operator*() { return mCurrent; }
void Next() {
MOZ_ASSERT(mCurrent, "Don't call Next() after we have no current node");
// We walk shadow roots immediately after their shadow host.
if (Element* element = Element::FromNode(mCurrent)) {
if (ShadowRoot* shadowRoot = element->GetShadowRoot()) {
mCurrent = shadowRoot;
mCurrent = mCurrent->GetNextNode(mRoots.LastElement());
void WalkOutOfShadowRootsIfNeeded() {
while (!mCurrent) {
// Nothing left under this root. Keep trying to pop the stack until we
// find a node or run out of stack.
nsINode* root = mRoots.PopLastElement();
if (mRoots.IsEmpty()) {
// No more roots to step out of; we're done. mCurrent is already set to
// null.
mCurrent =
// The current node we're at.
nsINode* mCurrent;
// Stack of roots that we're inside of right now. An empty stack can only
// happen when mCurrent is null (and hence we are done iterating).
// The default array size here is picked based on gut feeling. We want at
// least 1, since we will always add something to it in our constructor.
// Having a few more entries probably makes sense, because this is commonly
// used in cases when we know we have custom elements, and hence likely have
// shadow DOMs. But the exact value "4" was just picked because it sounded
// not too big, not too small. Feel free to replace it with something else
// based on actual data.
CopyableAutoTArray<nsINode*, 4> mRoots;
#ifdef DEBUG
// Make sure no one mutates the DOM while we're walking over it.
nsMutationGuard mMutationGuard;
#endif // DEBUG
} // namespace mozilla::dom
#endif // mozilla_dom_ShadowIncludingTreeIterator_h