Auto merge of #12469 - emilio:stylo, r=bholley

style: Rewrite the restyle hints code to allow different kinds of element snapshots.

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- [x] These changes do not require tests because refactoring.

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This is a rewrite for how style interfaces with its consumers in order to allow
different representations for an element snapshot.

This also changes the requirements of an element snapshot, requiring them to
only implement MatchAttr, instead of MatchAttrGeneric. This is important for
stylo since implementing MatchAttrGeneric is way more difficult for us given the
atom limitations. This also allows for more performant implementations in the
Gecko side of things.

I don't want to get this merged just yet, mainly because the stylo part is not
implemented, but I'd like early feedback from @bholley and/or @heycam: How do
you see this approach? I don't think we'll have much problem to implement
MatchAttr for our element snapshots, but... worth checking.

r? @heycam

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components/script/dom/bindings/trace.rs

@@ -89,8 +89,7 @@ use string_cache::{Atom, Namespace, QualName};
 use style::attr::{AttrIdentifier, AttrValue, LengthOrPercentageOrAuto};
 use style::element_state::*;
 use style::properties::PropertyDeclarationBlock;
-use style::restyle_hints::ElementSnapshot;
-use style::selector_impl::PseudoElement;
+use style::selector_impl::{PseudoElement, ElementSnapshot};
 use style::values::specified::Length;
 use url::Origin as UrlOrigin;
 use url::Url;

components/script/dom/document.rs

@@ -122,7 +122,7 @@ use std::sync::Arc;
 use string_cache::{Atom, QualName};
 use style::attr::AttrValue;
 use style::context::ReflowGoal;
-use style::restyle_hints::ElementSnapshot;
+use style::selector_impl::ElementSnapshot;
 use style::str::{split_html_space_chars, str_join};
 use style::stylesheets::Stylesheet;
 use time;
@@ -1851,15 +1851,21 @@ impl Document {
 
     pub fn element_state_will_change(&self, el: &Element) {
         let mut map = self.modified_elements.borrow_mut();
-        let snapshot = map.entry(JS::from_ref(el)).or_insert(ElementSnapshot::new());
+        let snapshot = map.entry(JS::from_ref(el))
+                          .or_insert_with(|| {
+                              ElementSnapshot::new(el.html_element_in_html_document())
+                          });
         if snapshot.state.is_none() {
             snapshot.state = Some(el.state());
         }
     }
 
     pub fn element_attr_will_change(&self, el: &Element) {
         let mut map = self.modified_elements.borrow_mut();
-        let mut snapshot = map.entry(JS::from_ref(el)).or_insert(ElementSnapshot::new());
+        let mut snapshot = map.entry(JS::from_ref(el))
+                              .or_insert_with(|| {
+                                  ElementSnapshot::new(el.html_element_in_html_document())
+                              });
         if snapshot.attrs.is_none() {
             let attrs = el.attrs()
                           .iter()

components/script/layout_wrapper.rs

@@ -60,8 +60,7 @@ use style::dom::{PresentationalHintsSynthetizer, OpaqueNode, TDocument, TElement
 use style::element_state::*;
 use style::properties::{PropertyDeclaration, PropertyDeclarationBlock};
 use style::refcell::{Ref, RefCell, RefMut};
-use style::restyle_hints::ElementSnapshot;
-use style::selector_impl::{NonTSPseudoClass, ServoSelectorImpl};
+use style::selector_impl::{ElementSnapshot, NonTSPseudoClass, ServoSelectorImpl};
 use style::sink::Push;
 use style::str::is_whitespace;
 use url::Url;

components/style/attr.rs

@@ -29,7 +29,7 @@ pub enum LengthOrPercentageOrAuto {
     Length(Au),
 }
 
-#[derive(PartialEq, Clone)]
+#[derive(PartialEq, Clone, Debug)]
 #[cfg_attr(feature = "servo", derive(HeapSizeOf))]
 pub enum AttrValue {
     String(String),

components/style/dom.rs

@@ -11,7 +11,7 @@ use data::PrivateStyleData;
 use element_state::ElementState;
 use properties::{ComputedValues, PropertyDeclaration, PropertyDeclarationBlock};
 use refcell::{Ref, RefMut};
-use restyle_hints::{ElementSnapshot, RESTYLE_DESCENDANTS, RESTYLE_LATER_SIBLINGS, RESTYLE_SELF, RestyleHint};
+use restyle_hints::{RESTYLE_DESCENDANTS, RESTYLE_LATER_SIBLINGS, RESTYLE_SELF, RestyleHint};
 use selector_impl::{ElementExt, SelectorImplExt};
 use selectors::Element;
 use selectors::matching::DeclarationBlock;
@@ -192,7 +192,8 @@ pub trait TDocument : Sized + Copy + Clone {
 
     fn root_node(&self) -> Option<Self::ConcreteNode>;
 
-    fn drain_modified_elements(&self) -> Vec<(Self::ConcreteElement, ElementSnapshot)>;
+    fn drain_modified_elements(&self) -> Vec<(Self::ConcreteElement,
+                                              <Self::ConcreteElement as ElementExt>::Snapshot)>;
 }
 
 pub trait PresentationalHintsSynthetizer {