1 files changed, 75 insertions, 0 deletions
diff --git a/servo/components/style/rule_tree/source.rs b/servo/components/style/rule_tree/source.rs
new file mode 100644
index 0000000000..76443692d7
--- /dev/null
+++ b/servo/components/style/rule_tree/source.rs
@@ -0,0 +1,75 @@
+/* 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 https://mozilla.org/MPL/2.0/. */
+
+#![forbid(unsafe_code)]
+
+use crate::properties::PropertyDeclarationBlock;
+use crate::shared_lock::{Locked, SharedRwLockReadGuard};
+use crate::stylesheets::StyleRule;
+use servo_arc::{Arc, ArcBorrow, ArcUnion, ArcUnionBorrow};
+use std::io::Write;
+use std::ptr;
+
+/// A style source for the rule node. It can either be a CSS style rule or a
+/// declaration block.
+///
+/// Note that, even though the declaration block from inside the style rule
+/// could be enough to implement the rule tree, keeping the whole rule provides
+/// more debuggability, and also the ability of show those selectors to
+/// devtools.
+#[derive(Clone, Debug)]
+pub struct StyleSource(ArcUnion<Locked<StyleRule>, Locked<PropertyDeclarationBlock>>);
+
+impl PartialEq for StyleSource {
+    fn eq(&self, other: &Self) -> bool {
+        ArcUnion::ptr_eq(&self.0, &other.0)
+    }
+}
+
+impl StyleSource {
+    /// Creates a StyleSource from a StyleRule.
+    pub fn from_rule(rule: Arc<Locked<StyleRule>>) -> Self {
+        StyleSource(ArcUnion::from_first(rule))
+    }
+
+    #[inline]
+    pub(super) fn key(&self) -> ptr::NonNull<()> {
+        self.0.ptr()
+    }
+
+    /// Creates a StyleSource from a PropertyDeclarationBlock.
+    pub fn from_declarations(decls: Arc<Locked<PropertyDeclarationBlock>>) -> Self {
+        StyleSource(ArcUnion::from_second(decls))
+    }
+
+    pub(super) fn dump<W: Write>(&self, guard: &SharedRwLockReadGuard, writer: &mut W) {
+        if let Some(ref rule) = self.0.as_first() {
+            let rule = rule.read_with(guard);
+            let _ = write!(writer, "{:?}", rule.selectors);
+        }
+
+        let _ = write!(writer, "  -> {:?}", self.read(guard).declarations());
+    }
+
+    /// Read the style source guard, and obtain thus read access to the
+    /// underlying property declaration block.
+    #[inline]
+    pub fn read<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a PropertyDeclarationBlock {
+        let block: &Locked<PropertyDeclarationBlock> = match self.0.borrow() {
+            ArcUnionBorrow::First(ref rule) => &rule.get().read_with(guard).block,
+            ArcUnionBorrow::Second(ref block) => block.get(),
+        };
+        block.read_with(guard)
+    }
+
+    /// Returns the style rule if applicable, otherwise None.
+    pub fn as_rule(&self) -> Option<ArcBorrow<Locked<StyleRule>>> {
+        self.0.as_first()
+    }
+
+    /// Returns the declaration block if applicable, otherwise None.
+    pub fn as_declarations(&self) -> Option<ArcBorrow<Locked<PropertyDeclarationBlock>>> {
+        self.0.as_second()
+    }
+}