author Neil Deakin <>
Thu, 19 Jul 2018 08:38:45 -0400
changeset 427271 68da215bdf87b5486a4f8c0a600ef77112f21ac4
parent 427268 17dd12ac3d4e9c1d5a13da773cc88a9c143955ec
child 431729 413c0f58374c3fd8af375ea1b680cb86c4a1492b
permissions -rw-r--r--
Bug 1461742, add a mechanism so that custom elements can implement interfaces akin to XBL implements. This is accomplished by an additional chrome-only callback getCustomInterface that can be implemented by custom elements, r=bz

/* -*- 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 */

#ifndef mozilla_dom_CustomElementRegistry_h
#define mozilla_dom_CustomElementRegistry_h

#include "js/GCHashTable.h"
#include "js/TypeDecls.h"
#include "mozilla/Attributes.h"
#include "mozilla/CycleCollectedJSContext.h" // for MicroTaskRunnable
#include "mozilla/ErrorResult.h"
#include "mozilla/dom/BindingDeclarations.h"
#include "mozilla/dom/CustomElementRegistryBinding.h"
#include "mozilla/dom/Element.h"
#include "mozilla/dom/FunctionBinding.h"
#include "mozilla/dom/WebComponentsBinding.h"
#include "nsCycleCollectionParticipant.h"
#include "nsGenericHTMLElement.h"
#include "nsWrapperCache.h"
#include "nsContentUtils.h"

class nsDocument;

namespace mozilla {
namespace dom {

struct CustomElementData;
struct ElementDefinitionOptions;
class CallbackFunction;
class CustomElementReaction;
class DocGroup;
class Function;
class Promise;

struct LifecycleCallbackArgs
  nsString name;
  nsString oldValue;
  nsString newValue;
  nsString namespaceURI;

struct LifecycleAdoptedCallbackArgs
  nsCOMPtr<nsIDocument> mOldDocument;
  nsCOMPtr<nsIDocument> mNewDocument;

class CustomElementCallback
  CustomElementCallback(Element* aThisObject,
                        nsIDocument::ElementCallbackType aCallbackType,
                        CallbackFunction* aCallback);
  void Traverse(nsCycleCollectionTraversalCallback& aCb) const;
  void Call();
  void SetArgs(LifecycleCallbackArgs& aArgs)
    MOZ_ASSERT(mType == nsIDocument::eAttributeChanged,
               "Arguments are only used by attribute changed callback.");
    mArgs = aArgs;

  void SetAdoptedCallbackArgs(LifecycleAdoptedCallbackArgs& aAdoptedCallbackArgs)
    MOZ_ASSERT(mType == nsIDocument::eAdopted,
      "Arguments are only used by adopted callback.");
    mAdoptedCallbackArgs = aAdoptedCallbackArgs;

  // The this value to use for invocation of the callback.
  RefPtr<Element> mThisObject;
  RefPtr<CallbackFunction> mCallback;
  // The type of callback (eCreated, eAttached, etc.)
  nsIDocument::ElementCallbackType mType;
  // Arguments to be passed to the callback,
  // used by the attribute changed callback.
  LifecycleCallbackArgs mArgs;
  LifecycleAdoptedCallbackArgs mAdoptedCallbackArgs;

class CustomElementConstructor final : public CallbackFunction
  explicit CustomElementConstructor(CallbackFunction* aOther)
    : CallbackFunction(aOther)

  already_AddRefed<Element> Construct(const char* aExecutionReason, ErrorResult& aRv);

// Each custom element has an associated callback queue and an element is
// being created flag.
struct CustomElementData

  // CustomElementData is only created on the element which is a custom element
  // or an upgrade candidate, so the state of an element without
  // CustomElementData is "uncustomized".
  enum class State {

  explicit CustomElementData(nsAtom* aType);
  CustomElementData(nsAtom* aType, State aState);

  // Custom element state as described in the custom element spec.
  State mState;
  // custom element reaction queue as described in the custom element spec.
  // There is 1 reaction in reaction queue, when 1) it becomes disconnected,
  // 2) it’s adopted into a new document, 3) its attributes are changed,
  // appended, removed, or replaced.
  // There are 3 reactions in reaction queue when doing upgrade operation,
  // e.g., create an element, insert a node.
  AutoTArray<UniquePtr<CustomElementReaction>, 3> mReactionQueue;

  void SetCustomElementDefinition(CustomElementDefinition* aDefinition);
  CustomElementDefinition* GetCustomElementDefinition();
  nsAtom* GetCustomElementType();

  void Traverse(nsCycleCollectionTraversalCallback& aCb) const;
  void Unlink();

  nsAtom* GetIs(Element* aElement)
    // If mType isn't the same as name atom, this is a customized built-in
    // element, which has 'is' value set.
    return aElement->NodeInfo()->NameAtom() == mType ? nullptr : mType.get();
  virtual ~CustomElementData() {}

  // Custom element type, for <button is="x-button"> or <x-button>
  // this would be x-button.
  RefPtr<nsAtom> mType;
  RefPtr<CustomElementDefinition> mCustomElementDefinition;


// The required information for a custom element as defined in:
struct CustomElementDefinition

  CustomElementDefinition(nsAtom* aType,
                          nsAtom* aLocalName,
                          Function* aConstructor,
                          nsTArray<RefPtr<nsAtom>>&& aObservedAttributes,
                          UniquePtr<LifecycleCallbacks>&& aCallbacks);

  // The type (name) for this custom element, for <button is="x-foo"> or <x-foo>
  // this would be x-foo.
  RefPtr<nsAtom> mType;

  // The localname to (e.g. <button is=type> -- this would be button).
  RefPtr<nsAtom> mLocalName;

  // The custom element constructor.
  RefPtr<CustomElementConstructor> mConstructor;

  // The list of attributes that this custom element observes.
  nsTArray<RefPtr<nsAtom>> mObservedAttributes;

  // The lifecycle callbacks to call for this custom element.
  UniquePtr<LifecycleCallbacks> mCallbacks;

  // A construction stack. Use nullptr to represent an "already constructed marker".
  nsTArray<RefPtr<Element>> mConstructionStack;

  bool IsCustomBuiltIn()
    return mType != mLocalName;

  bool IsInObservedAttributeList(nsAtom* aName)
    if (mObservedAttributes.IsEmpty()) {
      return false;

    return mObservedAttributes.Contains(aName);

  ~CustomElementDefinition() {}

class CustomElementReaction
  virtual ~CustomElementReaction() = default;
  virtual void Invoke(Element* aElement, ErrorResult& aRv) = 0;
  virtual void Traverse(nsCycleCollectionTraversalCallback& aCb) const = 0;

  bool IsUpgradeReaction()
    return mIsUpgradeReaction;

  bool mIsUpgradeReaction = false;

class CustomElementReactionsStack

    : mIsBackupQueueProcessing(false)
    , mRecursionDepth(0)
    , mIsElementQueuePushedForCurrentRecursionDepth(false)

  // Hold a strong reference of Element so that it does not get cycle collected
  // before the reactions in its reaction queue are invoked.
  // The element reaction queues are stored in CustomElementData.
  // We need to lookup ElementReactionQueueMap again to get relevant reaction queue.
  // The choice of 3 for the auto size here is based on running Custom Elements
  // wpt tests.
  typedef AutoTArray<RefPtr<Element>, 3> ElementQueue;

   * Enqueue a custom element upgrade reaction
  void EnqueueUpgradeReaction(Element* aElement,
                              CustomElementDefinition* aDefinition);

   * Enqueue a custom element callback reaction
  void EnqueueCallbackReaction(Element* aElement,
                               UniquePtr<CustomElementCallback> aCustomElementCallback);

   * [CEReactions] Before executing the algorithm's steps.
   * Increase the current recursion depth, and the element queue is pushed
   * lazily when we really enqueue reactions.
   * @return true if the element queue is pushed for "previous" recursion depth.
  bool EnterCEReactions()
    bool temp = mIsElementQueuePushedForCurrentRecursionDepth;
    // The is-element-queue-pushed flag is initially false when entering a new
    // recursion level. The original value will be cached in AutoCEReaction
    // and restored after leaving this recursion level.
    mIsElementQueuePushedForCurrentRecursionDepth = false;
    return temp;

   * [CEReactions] After executing the algorithm's steps.
   * Pop and invoke the element queue if it is created and pushed for current
   * recursion depth, then decrease the current recursion depth.
   * @param aCx JSContext used for handling exception thrown by algorithm's
   *            steps, this could be a nullptr.
   *        aWasElementQueuePushed used for restoring status after leaving
   *                               current recursion.
  void LeaveCEReactions(JSContext* aCx, bool aWasElementQueuePushed)

    if (mIsElementQueuePushedForCurrentRecursionDepth) {
      Maybe<JS::AutoSaveExceptionState> ases;
      if (aCx) {
    // Restore the is-element-queue-pushed flag cached in AutoCEReaction when
    // leaving the recursion level.
    mIsElementQueuePushedForCurrentRecursionDepth = aWasElementQueuePushed;

    MOZ_ASSERT_IF(!mRecursionDepth, mReactionsStack.IsEmpty());

  ~CustomElementReactionsStack() {};

   * Push a new element queue onto the custom element reactions stack.
  void CreateAndPushElementQueue();

   * Pop the element queue from the custom element reactions stack, and invoke
   * custom element reactions in that queue.
  void PopAndInvokeElementQueue();

  // The choice of 8 for the auto size here is based on gut feeling.
  AutoTArray<UniquePtr<ElementQueue>, 8> mReactionsStack;
  ElementQueue mBackupQueue;
  bool mIsBackupQueueProcessing;

  void InvokeBackupQueue();

   * Invoke custom element reactions
  void InvokeReactions(ElementQueue* aElementQueue, nsIGlobalObject* aGlobal);

  void Enqueue(Element* aElement, CustomElementReaction* aReaction);

  // Current [CEReactions] recursion depth.
  uint32_t mRecursionDepth;
  // True if the element queue is pushed into reaction stack for current
  // recursion depth. This will be cached in AutoCEReaction when entering a new
  // CEReaction recursion and restored after leaving the recursion.
  bool mIsElementQueuePushedForCurrentRecursionDepth;

  class BackupQueueMicroTask final : public mozilla::MicroTaskRunnable {
      explicit BackupQueueMicroTask(
        CustomElementReactionsStack* aReactionStack)
        : MicroTaskRunnable()
        , mReactionStack(aReactionStack)
                   "mIsBackupQueueProcessing should be initially false");
        mReactionStack->mIsBackupQueueProcessing = true;

      virtual void Run(AutoSlowOperation& aAso) override
        mReactionStack->mIsBackupQueueProcessing = false;

      RefPtr<CustomElementReactionsStack> mReactionStack;

class CustomElementRegistry final : public nsISupports,
                                    public nsWrapperCache
  // Allow nsDocument to access mCustomDefinitions and mCandidatesMap.
  friend class ::nsDocument;


  static bool IsCustomElementEnabled(JSContext* aCx, JSObject* aObject);
  static bool IsCustomElementEnabled(nsIDocument* aDoc);

  explicit CustomElementRegistry(nsPIDOMWindowInner* aWindow);

  class RunCustomElementCreationCallback : public mozilla::Runnable
    explicit RunCustomElementCreationCallback(CustomElementRegistry* aRegistry,
                                              nsAtom* aAtom,
                                              CustomElementCreationCallback* aCallback)
      : mozilla::Runnable("CustomElementRegistry::RunCustomElementCreationCallback")
      , mRegistry(aRegistry)
      , mAtom(aAtom)
      , mCallback(aCallback)
      RefPtr<CustomElementRegistry> mRegistry;
      RefPtr<nsAtom> mAtom;
      RefPtr<CustomElementCreationCallback> mCallback;

   * Looking up a custom element definition.
  CustomElementDefinition* LookupCustomElementDefinition(
    nsAtom* aNameAtom, nsAtom* aTypeAtom);

  CustomElementDefinition* LookupCustomElementDefinition(
    JSContext* aCx, JSObject *aConstructor) const;

  static void EnqueueLifecycleCallback(nsIDocument::ElementCallbackType aType,
                                       Element* aCustomElement,
                                       LifecycleCallbackArgs* aArgs,
                                       LifecycleAdoptedCallbackArgs* aAdoptedCallbackArgs,
                                       CustomElementDefinition* aDefinition);

   * Upgrade an element.
  static void Upgrade(Element* aElement, CustomElementDefinition* aDefinition, ErrorResult& aRv);

   * To allow native code to call methods of chrome-implemented custom elements,
   * a helper method may be defined in the custom element called
   * 'getCustomInterfaceCallback'. This method takes an IID and returns an
   * object which implements an XPCOM interface. If there is no
   * getCustomInterfaceCallback or the callback doesn't return an object,
   * QueryInterface is called on aElement to see if this interface is
   * implemented directly.
   * This returns null if aElement is not from a chrome document.
  static already_AddRefed<nsISupports> CallGetCustomInterface(
    Element* aElement, const nsIID& aIID);

   * Registers an unresolved custom element that is a candidate for
   * upgrade. |aTypeName| is the name of the custom element type, if it is not
   * provided, then element name is used. |aTypeName| should be provided
   * when registering a custom element that extends an existing
   * element. e.g. <button is="x-button">.
  void RegisterUnresolvedElement(Element* aElement,
                                 nsAtom* aTypeName = nullptr);

   * Unregister an unresolved custom element that is a candidate for
   * upgrade when a custom element is removed from tree.
  void UnregisterUnresolvedElement(Element* aElement,
                                   nsAtom* aTypeName = nullptr);

   * Register an element to be upgraded when the custom element creation
   * callback is executed.
   * To be used when LookupCustomElementDefinition() didn't return a definition,
   * but with the callback scheduled to be run.
  inline void RegisterCallbackUpgradeElement(Element* aElement,
                                             nsAtom* aTypeName = nullptr)
    if (mElementCreationCallbacksUpgradeCandidatesMap.IsEmpty()) {

    RefPtr<nsAtom> typeName = aTypeName;
    if (!typeName) {
      typeName = aElement->NodeInfo()->NameAtom();

    nsTHashtable<nsRefPtrHashKey<nsIWeakReference>>* elements =

    // If there isn't a table, there won't be a definition added by the callback.
    if (!elements) {

    nsWeakPtr elem = do_GetWeakReference(aElement);


  static UniquePtr<CustomElementCallback> CreateCustomElementCallback(
    nsIDocument::ElementCallbackType aType, Element* aCustomElement,
    LifecycleCallbackArgs* aArgs,
    LifecycleAdoptedCallbackArgs* aAdoptedCallbackArgs,
    CustomElementDefinition* aDefinition);

  void UpgradeCandidates(nsAtom* aKey,
                         CustomElementDefinition* aDefinition,
                         ErrorResult& aRv);

  typedef nsRefPtrHashtable<nsRefPtrHashKey<nsAtom>, CustomElementDefinition>
  typedef nsRefPtrHashtable<nsRefPtrHashKey<nsAtom>, CustomElementCreationCallback>
  typedef nsClassHashtable<nsRefPtrHashKey<nsAtom>,
  typedef JS::GCHashMap<JS::Heap<JSObject*>,
                        js::SystemAllocPolicy> ConstructorMap;

  // Hashtable for custom element definitions in web components.
  // Custom prototypes are stored in the compartment where definition was
  // defined.
  DefinitionMap mCustomDefinitions;

  // Hashtable for chrome-only callbacks that is called *before* we return
  // a CustomElementDefinition, when the typeAtom matches.
  // The callbacks are registered with the setElementCreationCallback method.
  ElementCreationCallbackMap mElementCreationCallbacks;

  // Hashtable for looking up definitions by using constructor as key.
  // Custom elements' name are stored here and we need to lookup
  // mCustomDefinitions again to get definitions.
  ConstructorMap mConstructors;

  typedef nsRefPtrHashtable<nsRefPtrHashKey<nsAtom>, Promise>
  WhenDefinedPromiseMap mWhenDefinedPromiseMap;

  // The "upgrade candidates map" from the web components spec. Maps from a
  // namespace id and local name to a list of elements to upgrade if that
  // element is registered as a custom element.
  CandidateMap mCandidatesMap;

  // If an element creation callback is found, the nsTHashtable for the
  // type is created here, and elements will later be upgraded.
  CandidateMap mElementCreationCallbacksUpgradeCandidatesMap;

  nsCOMPtr<nsPIDOMWindowInner> mWindow;

  // It is used to prevent reentrant invocations of element definition.
  bool mIsCustomDefinitionRunning;

  class MOZ_RAII AutoSetRunningFlag final {
      explicit AutoSetRunningFlag(CustomElementRegistry* aRegistry)
        : mRegistry(aRegistry)
                   "IsCustomDefinitionRunning flag should be initially false");
        mRegistry->mIsCustomDefinitionRunning = true;

      ~AutoSetRunningFlag() {
        mRegistry->mIsCustomDefinitionRunning = false;

      CustomElementRegistry* mRegistry;

  nsISupports* GetParentObject() const;

  DocGroup* GetDocGroup() const;

  virtual JSObject* WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto) override;

  void Define(JSContext* aCx, const nsAString& aName,
              Function& aFunctionConstructor,
              const ElementDefinitionOptions& aOptions, ErrorResult& aRv);

  void Get(JSContext* cx, const nsAString& name,
           JS::MutableHandle<JS::Value> aRetVal);

  already_AddRefed<Promise> WhenDefined(const nsAString& aName, ErrorResult& aRv);

  // Chrome-only method that give JS an opportunity to only load the custom
  // element definition script when needed.
  void SetElementCreationCallback(const nsAString& aName, CustomElementCreationCallback& aCallback, ErrorResult& aRv);

  void Upgrade(nsINode& aRoot);

class MOZ_RAII AutoCEReaction final {
    // JSContext is allowed to be a nullptr if we are guaranteeing that we're
    // not doing something that might throw but not finish reporting a JS
    // exception during the lifetime of the AutoCEReaction.
    AutoCEReaction(CustomElementReactionsStack* aReactionsStack, JSContext* aCx)
      : mReactionsStack(aReactionsStack)
      , mCx(aCx)
      mIsElementQueuePushedForPreviousRecursionDepth =

        mCx, mIsElementQueuePushedForPreviousRecursionDepth);

    RefPtr<CustomElementReactionsStack> mReactionsStack;
    JSContext* mCx;
    bool mIsElementQueuePushedForPreviousRecursionDepth;

} // namespace dom
} // namespace mozilla

#endif // mozilla_dom_CustomElementRegistry_h