1 files changed, 152 insertions, 0 deletions
diff --git a/servo/components/selectors/tree.rs b/servo/components/selectors/tree.rs
new file mode 100644
index 0000000000..fa150def0d
--- /dev/null
+++ b/servo/components/selectors/tree.rs
@@ -0,0 +1,152 @@
+/* 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/. */
+
+//! Traits that nodes must implement. Breaks the otherwise-cyclic dependency
+//! between layout and style.
+
+use crate::attr::{AttrSelectorOperation, CaseSensitivity, NamespaceConstraint};
+use crate::matching::{ElementSelectorFlags, MatchingContext};
+use crate::parser::SelectorImpl;
+use std::fmt::Debug;
+use std::ptr::NonNull;
+
+/// Opaque representation of an Element, for identity comparisons.
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+pub struct OpaqueElement(NonNull<()>);
+
+unsafe impl Send for OpaqueElement {}
+
+impl OpaqueElement {
+    /// Creates a new OpaqueElement from an arbitrarily-typed pointer.
+    pub fn new<T>(ptr: &T) -> Self {
+        unsafe {
+            OpaqueElement(NonNull::new_unchecked(
+                ptr as *const T as *const () as *mut (),
+            ))
+        }
+    }
+}
+
+pub trait Element: Sized + Clone + Debug {
+    type Impl: SelectorImpl;
+
+    /// Converts self into an opaque representation.
+    fn opaque(&self) -> OpaqueElement;
+
+    fn parent_element(&self) -> Option<Self>;
+
+    /// Whether the parent node of this element is a shadow root.
+    fn parent_node_is_shadow_root(&self) -> bool;
+
+    /// The host of the containing shadow root, if any.
+    fn containing_shadow_host(&self) -> Option<Self>;
+
+    /// The parent of a given pseudo-element, after matching a pseudo-element
+    /// selector.
+    ///
+    /// This is guaranteed to be called in a pseudo-element.
+    fn pseudo_element_originating_element(&self) -> Option<Self> {
+        debug_assert!(self.is_pseudo_element());
+        self.parent_element()
+    }
+
+    /// Whether we're matching on a pseudo-element.
+    fn is_pseudo_element(&self) -> bool;
+
+    /// Skips non-element nodes
+    fn prev_sibling_element(&self) -> Option<Self>;
+
+    /// Skips non-element nodes
+    fn next_sibling_element(&self) -> Option<Self>;
+
+    /// Skips non-element nodes
+    fn first_element_child(&self) -> Option<Self>;
+
+    fn is_html_element_in_html_document(&self) -> bool;
+
+    fn has_local_name(&self, local_name: &<Self::Impl as SelectorImpl>::BorrowedLocalName) -> bool;
+
+    /// Empty string for no namespace
+    fn has_namespace(&self, ns: &<Self::Impl as SelectorImpl>::BorrowedNamespaceUrl) -> bool;
+
+    /// Whether this element and the `other` element have the same local name and namespace.
+    fn is_same_type(&self, other: &Self) -> bool;
+
+    fn attr_matches(
+        &self,
+        ns: &NamespaceConstraint<&<Self::Impl as SelectorImpl>::NamespaceUrl>,
+        local_name: &<Self::Impl as SelectorImpl>::LocalName,
+        operation: &AttrSelectorOperation<&<Self::Impl as SelectorImpl>::AttrValue>,
+    ) -> bool;
+
+    fn match_non_ts_pseudo_class(
+        &self,
+        pc: &<Self::Impl as SelectorImpl>::NonTSPseudoClass,
+        context: &mut MatchingContext<Self::Impl>,
+    ) -> bool;
+
+    fn match_pseudo_element(
+        &self,
+        pe: &<Self::Impl as SelectorImpl>::PseudoElement,
+        context: &mut MatchingContext<Self::Impl>,
+    ) -> bool;
+
+    /// Sets selector flags on the elemnt itself or the parent, depending on the
+    /// flags, which indicate what kind of work may need to be performed when
+    /// DOM state changes.
+    fn apply_selector_flags(&self, flags: ElementSelectorFlags);
+
+    /// Whether this element is a `link`.
+    fn is_link(&self) -> bool;
+
+    /// Returns whether the element is an HTML <slot> element.
+    fn is_html_slot_element(&self) -> bool;
+
+    /// Returns the assigned <slot> element this element is assigned to.
+    ///
+    /// Necessary for the `::slotted` pseudo-class.
+    fn assigned_slot(&self) -> Option<Self> {
+        None
+    }
+
+    fn has_id(
+        &self,
+        id: &<Self::Impl as SelectorImpl>::Identifier,
+        case_sensitivity: CaseSensitivity,
+    ) -> bool;
+
+    fn has_class(
+        &self,
+        name: &<Self::Impl as SelectorImpl>::Identifier,
+        case_sensitivity: CaseSensitivity,
+    ) -> bool;
+
+    /// Returns the mapping from the `exportparts` attribute in the reverse
+    /// direction, that is, in an outer-tree -> inner-tree direction.
+    fn imported_part(
+        &self,
+        name: &<Self::Impl as SelectorImpl>::Identifier,
+    ) -> Option<<Self::Impl as SelectorImpl>::Identifier>;
+
+    fn is_part(&self, name: &<Self::Impl as SelectorImpl>::Identifier) -> bool;
+
+    /// Returns whether this element matches `:empty`.
+    ///
+    /// That is, whether it does not contain any child element or any non-zero-length text node.
+    /// See http://dev.w3.org/csswg/selectors-3/#empty-pseudo
+    fn is_empty(&self) -> bool;
+
+    /// Returns whether this element matches `:root`,
+    /// i.e. whether it is the root element of a document.
+    ///
+    /// Note: this can be false even if `.parent_element()` is `None`
+    /// if the parent node is a `DocumentFragment`.
+    fn is_root(&self) -> bool;
+
+    /// Returns whether this element should ignore matching nth child
+    /// selector.
+    fn ignores_nth_child_selectors(&self) -> bool {
+        false
+    }
+}