style: Allow calling GetBaseComputedStylesForElement for an unstyled …

…element.

Before this refactoring, getComputedStyle could have side effects, and left the
style data in the element, so we could never arrive there without data.

There are a few crashtests that caught this, but this was already broken if you
called animate() on an element deep in a display: none subtree.

MozReview-Commit-ID: 1AvOvhAyOP3

components/style/matching.rs

@@ -840,37 +840,6 @@ pub trait MatchMethods : TElement {
         // StyleChange::Changed conservatively.
         StyleDifference::new(damage, StyleChange::Changed)
     }
-
-    /// Returns computed values without animation and transition rules.
-    fn get_base_style(
-        &self,
-        context: &mut StyleContext<Self>,
-        style: &Arc<ComputedValues>,
-    ) -> Arc<ComputedValues> {
-        use style_resolver::StyleResolverForElement;
-
-        let rule_node = style.rules.as_ref().unwrap();
-        let without_animation_rules =
-            context.shared.stylist.rule_tree().remove_animation_rules(rule_node);
-        if without_animation_rules == *rule_node {
-            // Note that unwrapping here is fine, because the style is only
-            // incomplete during the styling process.
-            return style.clone();
-        }
-
-        // This currently ignores visited styles, which seems acceptable,
-        // as existing browsers don't appear to animate visited styles.
-        let inputs =
-            CascadeInputs {
-                rules: Some(without_animation_rules),
-                visited_rules: None,
-            };
-
-        let style =
-            StyleResolverForElement::new(*self, context, RuleInclusion::All)
-                .cascade_style_and_visited_with_default_parents(inputs);
-        style
-    }
 }
 
 impl<E: TElement> MatchMethods for E {}

ports/geckolib/glue.rs

@@ -654,19 +654,35 @@ pub extern "C" fn Servo_AnimationValue_Uncompute(value: RawServoAnimationValueBo
 #[no_mangle]
 pub extern "C" fn Servo_StyleSet_GetBaseComputedValuesForElement(raw_data: RawServoStyleSetBorrowed,
                                                                  element: RawGeckoElementBorrowed,
+                                                                 computed_values: ServoComputedValuesBorrowed,
                                                                  snapshots: *const ServoElementSnapshotTable,
                                                                  pseudo_type: CSSPseudoElementType)
                                                                  -> ServoComputedValuesStrong
 {
-    use style::matching::MatchMethods;
+    use style::style_resolver::StyleResolverForElement;
+
     debug_assert!(!snapshots.is_null());
+    let computed_values = ComputedValues::as_arc(&computed_values);
+
+    let rules = match computed_values.rules {
+        None => return computed_values.clone().into_strong(),
+        Some(ref rules) => rules,
+    };
 
     let doc_data = PerDocumentStyleData::from_ffi(raw_data).borrow();
-    let global_style_data = &*GLOBAL_STYLE_DATA;
-    let guard = global_style_data.shared_lock.read();
+    let without_animations =
+        doc_data.stylist.rule_tree().remove_animation_rules(rules);
+
+    if without_animations == *rules {
+        return computed_values.clone().into_strong();
+    }
 
     let element = GeckoElement(element);
-    let element_data = element.borrow_data().unwrap();
+
+    let element_data = match element.borrow_data() {
+        Some(data) => data,
+        None => return computed_values.clone().into_strong(),
+    };
     let styles = &element_data.styles;
 
     if let Some(pseudo) = PseudoElement::from_pseudo_type(pseudo_type) {
@@ -678,6 +694,8 @@ pub extern "C" fn Servo_StyleSet_GetBaseComputedValuesForElement(raw_data: RawSe
             .clone().into_strong();
     }
 
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
     let shared = create_shared_context(&global_style_data,
                                        &guard,
                                        &doc_data,
@@ -689,10 +707,17 @@ pub extern "C" fn Servo_StyleSet_GetBaseComputedValuesForElement(raw_data: RawSe
         thread_local: &mut tlc,
     };
 
-    element.get_base_style(
-        &mut context,
-        styles.primary(),
-    ).into_strong()
+    // This currently ignores visited styles, which seems acceptable, as
+    // existing browsers don't appear to animate visited styles.
+    let inputs =
+        CascadeInputs {
+            rules: Some(without_animations),
+            visited_rules: None,
+        };
+
+    StyleResolverForElement::new(element, &mut context, RuleInclusion::All)
+        .cascade_style_and_visited_with_default_parents(inputs)
+        .into_strong()
 }
 
 #[no_mangle]