Auto merge of #17427 - CJKu:cku-master, r=emilio

Stylo: Correct style match for element instances under a use-element …

<!-- Please describe your changes on the following line: -->
This patch is the last one of bug 265894.
It fixes two things:
1. Do not cross shadow tree boundary while matching rules.
2. Change display value to 'inline' while cloning a root symbol element instance.

Bugzilla link:
https://bugzilla.mozilla.org/show_bug.cgi?id=265894
---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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components/selectors/matching.rs

@@ -532,8 +532,12 @@ fn matches_complex_selector_internal<E, F>(mut selector_iter: SelectorIter<E::Im
                      SelectorMatchingResult::NotMatchedAndRestartFromClosestDescendant)
                 }
                 Combinator::Child | Combinator::Descendant => {
-                    (element.parent_element(),
-                     SelectorMatchingResult::NotMatchedGlobally)
+                    if element.blocks_ancestor_combinators() {
+                        (None, SelectorMatchingResult::NotMatchedGlobally)
+                    } else {
+                        (element.parent_element(),
+                         SelectorMatchingResult::NotMatchedGlobally)
+                    }
                 }
                 Combinator::PseudoElement => {
                     (element.pseudo_element_originating_element(),

components/selectors/tree.rs

@@ -85,4 +85,11 @@ pub trait Element: Sized + Debug {
     /// Note: this can be false even if `.parent_element()` is `None`
     /// if the parent node is a `DocumentFragment`.
     fn is_root(&self) -> bool;
+
+    /// Return true if we want to stop lookup ancestor of the current
+    /// element while matching complex selectors with descendant/child
+    /// combinator.
+    fn blocks_ancestor_combinators(&self) -> bool {
+        false
+    }
 }

components/style/gecko/non_ts_pseudo_class_list.rs

@@ -111,6 +111,7 @@ macro_rules! apply_non_ts_list {
                 ("-moz-last-node", MozLastNode, lastNode, _, _),
                 ("-moz-only-whitespace", MozOnlyWhitespace, mozOnlyWhitespace, _, _),
                 ("-moz-native-anonymous", MozNativeAnonymous, mozNativeAnonymous, _, PSEUDO_CLASS_INTERNAL),
+                ("-moz-use-shadow-tree-root", MozUseShadowTreeRoot, mozUseShadowTreeRoot, _, PSEUDO_CLASS_INTERNAL),
                 ("-moz-is-html", MozIsHTML, mozIsHTML, _, _),
                 ("-moz-placeholder", MozPlaceholder, mozPlaceholder, _, _),
             ],

components/style/gecko/wrapper.rs

@@ -1645,7 +1645,8 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             }
             NonTSPseudoClass::MozTableBorderNonzero |
             NonTSPseudoClass::MozBrowserFrame |
-            NonTSPseudoClass::MozNativeAnonymous => unsafe {
+            NonTSPseudoClass::MozNativeAnonymous |
+            NonTSPseudoClass::MozUseShadowTreeRoot => unsafe {
                 Gecko_MatchesElement(pseudo_class.to_gecko_pseudoclasstype().unwrap(), self.0)
             },
             NonTSPseudoClass::MozIsHTML => {
@@ -1734,6 +1735,24 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
         node_info.mInner.mNamespaceID == (structs::root::kNameSpaceID_XHTML as i32) &&
         node.owner_doc().mType == structs::root::nsIDocument_Type::eHTML
     }
+
+    fn blocks_ancestor_combinators(&self) -> bool {
+        use gecko_bindings::structs::NODE_IS_ANONYMOUS_ROOT;
+        if self.flags() & (NODE_IS_ANONYMOUS_ROOT as u32) == 0 {
+            return false
+        }
+
+        match self.parent_element() {
+            Some(e) => {
+                // If this element is the shadow root of an use-element shadow
+                // tree, according to the spec, we should not match rules
+                // cross the shadow DOM boundary.
+                e.get_local_name().as_ptr() == atom!("use").as_ptr() &&
+                e.get_namespace() == &*Namespace(atom!("http://www.w3.org/2000/svg"))
+            },
+            None => false,
+        }
+    }
 }
 
 /// A few helpers to help with attribute selectors and snapshotting.