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diff --git a/layout/style/DeclarationBlock.h b/layout/style/DeclarationBlock.h
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+/* -*- 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"
+#include "nsString.h"
+
+class nsHTMLCSSStyleSheet;
+
+namespace mozilla {
+
+namespace css {
+class Declaration;
+class Rule;
+} // namespace css
+
+class DeclarationBlock final {
+ DeclarationBlock(const DeclarationBlock& aCopy)
+ : mRaw(Servo_DeclarationBlock_Clone(aCopy.mRaw).Consume()),
+ mImmutable(false),
+ mIsDirty(false) {
+ mContainer.mRaw = 0;
+ }
+
+ public:
+ explicit DeclarationBlock(already_AddRefed<StyleLockedDeclarationBlock> aRaw)
+ : mRaw(aRaw), mImmutable(false), mIsDirty(false) {
+ mContainer.mRaw = 0;
+ }
+
+ DeclarationBlock()
+ : DeclarationBlock(Servo_DeclarationBlock_CreateEmpty().Consume()) {}
+
+ NS_INLINE_DECL_THREADSAFE_REFCOUNTING(DeclarationBlock)
+
+ already_AddRefed<DeclarationBlock> Clone() const {
+ return do_AddRef(new DeclarationBlock(*this));
+ }
+
+ /**
+ * Return whether |this| may be modified.
+ */
+ bool IsMutable() const { return !mImmutable; }
+
+ /**
+ * Crash in debug builds if |this| cannot be modified.
+ */
+ void AssertMutable() const {
+ MOZ_ASSERT(IsMutable(), "someone forgot to call EnsureMutable");
+ MOZ_ASSERT(!OwnerIsReadOnly(), "User Agent sheets shouldn't be modified");
+ }
+
+ /**
+ * Mark this declaration as unmodifiable.
+ */
+ 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.
+ */
+ already_AddRefed<DeclarationBlock> EnsureMutable() {
+ MOZ_ASSERT(!OwnerIsReadOnly());
+
+ 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.
+ //
+ // FIXME(emilio, bug 1606413): This is a hack for ::first-line and
+ // transitions starting due to CSSOM changes when other transitions are
+ // already running. Try to simplify this setup, so that rule tree updates
+ // find the mutated declaration block properly rather than having to
+ // insert the cloned declaration in the tree.
+ 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;
+ }
+
+ bool IsReadOnly() const;
+
+ size_t SizeofIncludingThis(MallocSizeOf);
+
+ static already_AddRefed<DeclarationBlock> FromCssText(
+ const nsACString& aCssText, URLExtraData* aExtraData,
+ nsCompatibility aMode, css::Loader* aLoader, StyleCssRuleType aRuleType) {
+ RefPtr<StyleLockedDeclarationBlock> raw =
+ Servo_ParseStyleAttribute(&aCssText, aExtraData, aMode, aLoader,
+ aRuleType)
+ .Consume();
+ return MakeAndAddRef<DeclarationBlock>(raw.forget());
+ }
+
+ static already_AddRefed<DeclarationBlock> FromCssText(
+ const nsAString& aCssText, URLExtraData* aExtraData,
+ nsCompatibility aMode, css::Loader* aLoader, StyleCssRuleType aRuleType) {
+ NS_ConvertUTF16toUTF8 value(aCssText);
+ return FromCssText(value, aExtraData, aMode, aLoader, aRuleType);
+ }
+
+ StyleLockedDeclarationBlock* Raw() const { return mRaw; }
+
+ void ToString(nsACString& aResult) const {
+ Servo_DeclarationBlock_GetCssText(mRaw, &aResult);
+ }
+
+ uint32_t Count() const { return Servo_DeclarationBlock_Count(mRaw); }
+
+ bool GetNthProperty(uint32_t aIndex, nsACString& aReturn) const {
+ aReturn.Truncate();
+ return Servo_DeclarationBlock_GetNthProperty(mRaw, aIndex, &aReturn);
+ }
+
+ void GetPropertyValue(const nsACString& aProperty, nsACString& aValue) const {
+ Servo_DeclarationBlock_GetPropertyValue(mRaw, &aProperty, &aValue);
+ }
+
+ void GetPropertyValueByID(nsCSSPropertyID aPropID, nsACString& aValue) const {
+ Servo_DeclarationBlock_GetPropertyValueById(mRaw, aPropID, &aValue);
+ }
+
+ bool GetPropertyIsImportant(const nsACString& aProperty) const {
+ return Servo_DeclarationBlock_GetPropertyIsImportant(mRaw, &aProperty);
+ }
+
+ // Returns whether the property was removed.
+ bool RemoveProperty(const nsACString& aProperty,
+ DeclarationBlockMutationClosure aClosure = {}) {
+ AssertMutable();
+ return Servo_DeclarationBlock_RemoveProperty(mRaw, &aProperty, aClosure);
+ }
+
+ // Returns whether the property was removed.
+ bool RemovePropertyByID(nsCSSPropertyID aProperty,
+ DeclarationBlockMutationClosure aClosure = {}) {
+ AssertMutable();
+ return Servo_DeclarationBlock_RemovePropertyById(mRaw, aProperty, aClosure);
+ }
+
+ private:
+ ~DeclarationBlock() = default;
+
+ bool OwnerIsReadOnly() const;
+
+ 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<StyleLockedDeclarationBlock> 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