gecko-dev/layout/style/DeclarationBlock.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 a declaration block in a CSS stylesheet, or of
 * a style attribute
 */

#ifndef mozilla_DeclarationBlock_h
#define mozilla_DeclarationBlock_h

#include "mozilla/Atomics.h"
#include "mozilla/ServoBindings.h"

#include "nsCSSPropertyID.h"

class nsHTMLCSSStyleSheet;

namespace mozilla {

namespace css {
class Declaration;
class Rule;
} // namespace css

class DeclarationBlock final
{
public:
  explicit DeclarationBlock(
    already_AddRefed<RawServoDeclarationBlock> aRaw)
    : mRaw(aRaw)
    , mImmutable(false)
    , mIsDirty(false)
  {
    mContainer.mRaw = 0;
  }

  DeclarationBlock()
    : DeclarationBlock(Servo_DeclarationBlock_CreateEmpty().Consume()) {}

  DeclarationBlock(const DeclarationBlock& aCopy)
    : mRaw(Servo_DeclarationBlock_Clone(aCopy.mRaw).Consume())
    , mImmutable(false)
    , mIsDirty(false)
  {
    mContainer.mRaw = 0;
  }

  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(DeclarationBlock)

  inline already_AddRefed<DeclarationBlock> Clone() const
  {
    return do_AddRef(new DeclarationBlock(*this));
  }

  /**
   * Return whether |this| may be modified.
   */
  bool IsMutable() const {
    return !mImmutable;
  }

  /**
   * Crash if |this| cannot be modified.
   */
  void AssertMutable() const {
    MOZ_ASSERT(IsMutable(), "someone forgot to call EnsureMutable");
  }

  /**
   * Mark this declaration as unmodifiable.  It's 'const' so it can
   * be called from ToString.
   */
  void SetImmutable() { mImmutable = true; }

  /**
   * Return whether |this| has been restyled after modified.
   */
  bool IsDirty() const { return mIsDirty; }

  /**
   * Mark this declaration as dirty.
   */
  void SetDirty() { mIsDirty = true; }

  /**
   * Mark this declaration as not dirty.
   */
  void UnsetDirty() { mIsDirty = false; }

  /**
   * Copy |this|, if necessary to ensure that it can be modified.
   */
  inline already_AddRefed<DeclarationBlock>
  EnsureMutable()
  {
    if (!IsDirty()) {
      // In stylo, the old DeclarationBlock is stored in element's rule node tree
      // directly, to avoid new values replacing the DeclarationBlock in the tree
      // directly, we need to copy the old one here if we haven't yet copied.
      // As a result the new value does not replace rule node tree until traversal
      // happens.
      return Clone();
    }

    if (!IsMutable()) {
      return Clone();
    }
    return do_AddRef(this);
  }

  void SetOwningRule(css::Rule* aRule) {
    MOZ_ASSERT(!mContainer.mOwningRule || !aRule,
               "should never overwrite one rule with another");
    mContainer.mOwningRule = aRule;
  }

  css::Rule* GetOwningRule() const {
    if (mContainer.mRaw & 0x1) {
      return nullptr;
    }
    return mContainer.mOwningRule;
  }

  void SetHTMLCSSStyleSheet(nsHTMLCSSStyleSheet* aHTMLCSSStyleSheet) {
    MOZ_ASSERT(!mContainer.mHTMLCSSStyleSheet || !aHTMLCSSStyleSheet,
               "should never overwrite one sheet with another");
    mContainer.mHTMLCSSStyleSheet = aHTMLCSSStyleSheet;
    if (aHTMLCSSStyleSheet) {
      mContainer.mRaw |= uintptr_t(1);
    }
  }

  nsHTMLCSSStyleSheet* GetHTMLCSSStyleSheet() const {
    if (!(mContainer.mRaw & 0x1)) {
      return nullptr;
    }
    auto c = mContainer;
    c.mRaw &= ~uintptr_t(1);
    return c.mHTMLCSSStyleSheet;
  }

  static already_AddRefed<DeclarationBlock>
  FromCssText(const nsAString& aCssText, URLExtraData* aExtraData,
              nsCompatibility aMode, css::Loader* aLoader);

  RawServoDeclarationBlock* Raw() const { return mRaw; }
  RawServoDeclarationBlock* const* RefRaw() const
  {
    static_assert(sizeof(RefPtr<RawServoDeclarationBlock>) ==
                  sizeof(RawServoDeclarationBlock*),
                  "RefPtr should just be a pointer");
    return reinterpret_cast<RawServoDeclarationBlock* const*>(&mRaw);
  }

  const RawServoDeclarationBlockStrong* RefRawStrong() const
  {
    static_assert(sizeof(RefPtr<RawServoDeclarationBlock>) ==
                  sizeof(RawServoDeclarationBlock*),
                  "RefPtr should just be a pointer");
    static_assert(sizeof(RefPtr<RawServoDeclarationBlock>) ==
                  sizeof(RawServoDeclarationBlockStrong),
                  "RawServoDeclarationBlockStrong should be the same as RefPtr");
    return reinterpret_cast<const RawServoDeclarationBlockStrong*>(&mRaw);
  }

  void ToString(nsAString& aResult) const {
    Servo_DeclarationBlock_GetCssText(mRaw, &aResult);
  }

  uint32_t Count() const {
    return Servo_DeclarationBlock_Count(mRaw);
  }

  bool GetNthProperty(uint32_t aIndex, nsAString& aReturn) const {
    aReturn.Truncate();
    return Servo_DeclarationBlock_GetNthProperty(mRaw, aIndex, &aReturn);
  }

  void GetPropertyValue(const nsAString& aProperty,
                        nsAString& aValue) const;
  void GetPropertyValueByID(nsCSSPropertyID aPropID,
                            nsAString& aValue) const;
  bool GetPropertyIsImportant(const nsAString& aProperty) const;
  // Returns whether the property was removed.
  bool RemoveProperty(const nsAString& aProperty);
  // Returns whether the property was removed.
  bool RemovePropertyByID(nsCSSPropertyID aProperty);

private:
  ~DeclarationBlock() = default;
  union {
    // We only ever have one of these since we have an
    // nsHTMLCSSStyleSheet only for style attributes, and style
    // attributes never have an owning rule.

    // It's an nsHTMLCSSStyleSheet if the low bit is set.

    uintptr_t mRaw;

    // The style rule that owns this declaration.  May be null.
    css::Rule* mOwningRule;

    // The nsHTMLCSSStyleSheet that is responsible for this declaration.
    // Only non-null for style attributes.
    nsHTMLCSSStyleSheet* mHTMLCSSStyleSheet;
  } mContainer;

  RefPtr<RawServoDeclarationBlock> mRaw;

  // set when declaration put in the rule tree;
  bool mImmutable;

  // True if this declaration has not been restyled after modified.
  //
  // Since we can clear this flag from style worker threads, we use an Atomic.
  //
  // Note that although a single DeclarationBlock can be shared between
  // different rule nodes (due to the style="" attribute cache), whenever a
  // DeclarationBlock has its mIsDirty flag set to true, we always clone it to
  // a unique object first. So when we clear this flag during Servo traversal,
  // we know that we are clearing it on a DeclarationBlock that has a single
  // reference, and there is no problem with another user of the same
  // DeclarationBlock thinking that it is not dirty.
  Atomic<bool, MemoryOrdering::Relaxed> mIsDirty;
};

} // namespace mozilla

#endif // mozilla_DeclarationBlock_h