style: Add a very simple invalidation-based querySelector.

MozReview-Commit-ID: Fimc8tz4OWX
Signed-off-by: Emilio Cobos Álvarez <emilio@crisal.io>

components/style/dom_apis.rs

@@ -6,8 +6,11 @@
 //! and Gecko.
 
 use context::QuirksMode;
+use dom::{TElement, TNode};
+use invalidation::element::invalidator::{Invalidation, InvalidationProcessor, InvalidationVector};
 use selectors::{Element, NthIndexCache, SelectorList};
 use selectors::matching::{self, MatchingContext, MatchingMode};
+use smallvec::SmallVec;
 
 /// <https://dom.spec.whatwg.org/#dom-element-matches>
 pub fn element_matches<E>(
@@ -57,3 +60,128 @@ where
 
     return None;
 }
+
+/// The result of a querySelector call.
+pub type QuerySelectorResult<E> = SmallVec<[E; 128]>;
+
+/// The query kind we're doing (either only the first descendant that matches or
+/// all of them).
+pub enum QuerySelectorKind {
+    /// <https://dom.spec.whatwg.org/#dom-parentnode-queryselectorall>
+    All,
+    /// <https://dom.spec.whatwg.org/#dom-parentnode-queryselector>
+    First,
+}
+
+struct QuerySelectorProcessor<'a, E: TElement + 'a> {
+    kind: QuerySelectorKind,
+    results: &'a mut QuerySelectorResult<E>,
+    matching_context: MatchingContext<'a, E::Impl>,
+    selector_list: &'a SelectorList<E::Impl>,
+}
+
+impl<'a, E> InvalidationProcessor<'a, E> for QuerySelectorProcessor<'a, E>
+where
+    E: TElement + 'a,
+{
+    fn collect_invalidations(
+        &mut self,
+        _element: E,
+        self_invalidations: &mut InvalidationVector<'a>,
+        descendant_invalidations: &mut InvalidationVector<'a>,
+        _sibling_invalidations: &mut InvalidationVector<'a>,
+    ) -> bool {
+        // FIXME(emilio): If the element is not a root element, and
+        // selector_list has any descendant combinator, we need to do extra work
+        // in order to handle properly things like:
+        //
+        //   <div id="a">
+        //     <div id="b">
+        //       <div id="c"></div>
+        //     </div>
+        //   </div>
+        //
+        // b.querySelector('#a div'); // Should return "c".
+        //
+        let target_vector =
+            if self.matching_context.scope_element.is_some() {
+                descendant_invalidations
+            } else {
+                self_invalidations
+            };
+
+        for selector in self.selector_list.0.iter() {
+            target_vector.push(Invalidation::new(selector, 0))
+        }
+
+        false
+    }
+
+    fn matching_context(&mut self) -> &mut MatchingContext<'a, E::Impl> {
+        &mut self.matching_context
+    }
+
+    fn should_process_descendants(&mut self, _: E) -> bool {
+        match self.kind {
+            QuerySelectorKind::All => true,
+            QuerySelectorKind::First => self.results.is_empty(),
+        }
+    }
+
+    fn invalidated_self(&mut self, e: E) {
+        self.results.push(e);
+    }
+
+    fn recursion_limit_exceeded(&mut self, _e: E) {}
+    fn invalidated_descendants(&mut self, _e: E, _child: E) {}
+}
+
+/// <https://dom.spec.whatwg.org/#dom-parentnode-queryselector>
+pub fn query_selector<E: TElement>(
+    root: E::ConcreteNode,
+    selector_list: &SelectorList<E::Impl>,
+    results: &mut QuerySelectorResult<E>,
+    kind: QuerySelectorKind,
+    quirks_mode: QuirksMode,
+) {
+    use invalidation::element::invalidator::TreeStyleInvalidator;
+
+    let mut nth_index_cache = NthIndexCache::default();
+    let mut matching_context = MatchingContext::new(
+        MatchingMode::Normal,
+        None,
+        Some(&mut nth_index_cache),
+        quirks_mode,
+    );
+
+    let root_element = root.as_element();
+    matching_context.scope_element = root_element.map(|e| e.opaque());
+
+    let mut processor = QuerySelectorProcessor {
+        kind,
+        results,
+        matching_context,
+        selector_list,
+    };
+
+    match root_element {
+        Some(e) => {
+            TreeStyleInvalidator::new(
+                e,
+                /* stack_limit_checker = */ None,
+                &mut processor,
+            ).invalidate();
+        }
+        None => {
+            for node in root.dom_children() {
+                if let Some(e) = node.as_element() {
+                    TreeStyleInvalidator::new(
+                        e,
+                        /* stack_limit_checker = */ None,
+                        &mut processor,
+                    ).invalidate();
+                }
+            }
+        }
+    }
+}