Auto merge of #17206 - heycam:lang-snapshots, r=emilio

match :lang() against snapshots correctly

Reviewed in https://bugzilla.mozilla.org/show_bug.cgi?id=1365162.

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/17206)
<!-- Reviewable:end -->

2 files changed, 6 insertions, 60 deletions

diff --git a/components/script/dom/bindings/str.rs b/components/script/dom/bindings/str.rs
index 6cb17fae4e3..4e579044491 100644
--- a/components/script/dom/bindings/str.rs
+++ b/components/script/dom/bindings/str.rs
@@ -113,63 +113,6 @@ pub fn is_token(s: &[u8]) -> bool {
     })
 }
 
-/// Returns whether the language is matched, as defined by
-/// [RFC 4647](https://tools.ietf.org/html/rfc4647#section-3.3.2).
-pub fn extended_filtering(tag: &str, range: &str) -> bool {
-    let lang_ranges: Vec<&str> = range.split(',').collect();
-
-    lang_ranges.iter().any(|&lang_range| {
-        // step 1
-        let range_subtags: Vec<&str> = lang_range.split('\x2d').collect();
-        let tag_subtags: Vec<&str> = tag.split('\x2d').collect();
-
-        let mut range_iter = range_subtags.iter();
-        let mut tag_iter = tag_subtags.iter();
-
-        // step 2
-        // Note: [Level-4 spec](https://drafts.csswg.org/selectors/#lang-pseudo) check for wild card
-        if let (Some(range_subtag), Some(tag_subtag)) = (range_iter.next(), tag_iter.next()) {
-            if !(range_subtag.eq_ignore_ascii_case(tag_subtag) || range_subtag.eq_ignore_ascii_case("*")) {
-                return false;
-            }
-        }
-
-        let mut current_tag_subtag = tag_iter.next();
-
-        // step 3
-        for range_subtag in range_iter {
-            // step 3a
-            if range_subtag.eq_ignore_ascii_case("*") {
-                continue;
-            }
-            match current_tag_subtag.clone() {
-                Some(tag_subtag) => {
-                    // step 3c
-                    if range_subtag.eq_ignore_ascii_case(tag_subtag) {
-                        current_tag_subtag = tag_iter.next();
-                        continue;
-                    } else {
-                        // step 3d
-                        if tag_subtag.len() == 1 {
-                            return false;
-                        } else {
-                            // else step 3e - continue with loop
-                            current_tag_subtag = tag_iter.next();
-                            if current_tag_subtag.is_none() {
-                                return false;
-                            }
-                        }
-                    }
-                },
-                // step 3b
-                None => { return false; }
-            }
-        }
-        // step 4
-        true
-    })
-}
-
 
 /// A DOMString.
 ///
diff --git a/components/script/dom/element.rs b/components/script/dom/element.rs
index c0d4b6b700a..cb882f53463 100644
--- a/components/script/dom/element.rs
+++ b/components/script/dom/element.rs
@@ -26,7 +26,7 @@ use dom::bindings::js::{JS, LayoutJS, MutNullableJS};
 use dom::bindings::js::{Root, RootedReference};
 use dom::bindings::refcounted::{Trusted, TrustedPromise};
 use dom::bindings::reflector::DomObject;
-use dom::bindings::str::{DOMString, extended_filtering};
+use dom::bindings::str::DOMString;
 use dom::bindings::xmlname::{namespace_from_domstring, validate_and_extract, xml_name_type};
 use dom::bindings::xmlname::XMLName::InvalidXMLName;
 use dom::characterdata::CharacterData;
@@ -106,6 +106,7 @@ use style::properties::longhands::{self, background_image, border_spacing, font_
 use style::restyle_hints::RestyleHint;
 use style::rule_tree::CascadeLevel;
 use style::selector_parser::{NonTSPseudoClass, PseudoElement, RestyleDamage, SelectorImpl, SelectorParser};
+use style::selector_parser::extended_filtering;
 use style::shared_lock::{SharedRwLock, Locked};
 use style::sink::Push;
 use style::stylearc::Arc;
@@ -2464,8 +2465,10 @@ impl<'a> ::selectors::Element for Root<Element> {
                     .map_or(false, |attr| attr.value().eq(expected_value))
             }
 
-            // FIXME(#15746): This is wrong, we need to instead use extended filtering as per RFC4647
-            //                https://tools.ietf.org/html/rfc4647#section-3.3.2
+            // FIXME(heycam): This is wrong, since extended_filtering accepts
+            // a string containing commas (separating each language tag in
+            // a list) but the pseudo-class instead should be parsing and
+            // storing separate <ident> or <string>s for each language tag.
             NonTSPseudoClass::Lang(ref lang) => extended_filtering(&*self.get_lang(), &*lang),
 
             NonTSPseudoClass::ReadOnly =>