ID and class selectors are ASCII case-insensitive in quirks mode.

https://bugzilla.mozilla.org/show_bug.cgi?id=1363778

components/selectors/attr.rs

@@ -127,7 +127,7 @@ pub static SELECTOR_WHITESPACE: &'static [char] = &[' ', '\t', '\n', '\r', '\x0C
 
 #[derive(Eq, PartialEq, Clone, Copy, Debug)]
 pub enum ParsedCaseSensitivity {
-    CaseSensitive,  // Selectors spec says language-defined, but HTML says sensitive.
+    CaseSensitive,
     AsciiCaseInsensitive,
     AsciiCaseInsensitiveIfInHtmlElementInHtmlDocument,
 }
@@ -150,7 +150,7 @@ impl ParsedCaseSensitivity {
 
 #[derive(Eq, PartialEq, Clone, Copy, Debug)]
 pub enum CaseSensitivity {
-    CaseSensitive,  // Selectors spec says language-defined, but HTML says sensitive.
+    CaseSensitive,
     AsciiCaseInsensitive,
 }
 

components/selectors/matching.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use attr::{ParsedAttrSelectorOperation, AttrSelectorOperation, NamespaceConstraint};
+use attr::{ParsedAttrSelectorOperation, AttrSelectorOperation, NamespaceConstraint, CaseSensitivity};
 use bloom::{BLOOM_HASH_MASK, BloomFilter};
 use parser::{AncestorHashes, Combinator, Component, LocalName};
 use parser::{Selector, SelectorImpl, SelectorIter, SelectorList};
@@ -666,12 +666,21 @@ fn matches_simple_selector<E, F>(
             let ns = ::parser::namespace_empty_string::<E::Impl>();
             element.get_namespace() == ns.borrow()
         }
-        // TODO: case-sensitivity depends on the document type and quirks mode
         Component::ID(ref id) => {
-            element.get_id().map_or(false, |attr| attr == *id)
+            let case_sensitivity = if element.in_quirks_mode_document() {
+                CaseSensitivity::AsciiCaseInsensitive
+            } else {
+                CaseSensitivity::CaseSensitive
+            };
+            element.has_id(id, case_sensitivity)
         }
         Component::Class(ref class) => {
-            element.has_class(class)
+            let case_sensitivity = if element.in_quirks_mode_document() {
+                CaseSensitivity::AsciiCaseInsensitive
+            } else {
+                CaseSensitivity::CaseSensitive
+            };
+            element.has_class(class, case_sensitivity)
         }
         Component::AttributeInNoNamespaceExists { ref local_name, ref local_name_lower } => {
             let is_html = element.is_html_element_in_html_document();

components/selectors/parser.rs

@@ -1385,7 +1385,10 @@ fn parse_attribute_flags<'i, 't, E>(input: &mut CssParser<'i, 't>)
                                     -> Result<ParsedCaseSensitivity,
                                               ParseError<'i, SelectorParseError<'i, E>>> {
     match input.next() {
-        Err(_) => Ok(ParsedCaseSensitivity::CaseSensitive),
+        Err(_) => {
+            // Selectors spec says language-defined, but HTML says sensitive.
+            Ok(ParsedCaseSensitivity::CaseSensitive)
+        }
         Ok(Token::Ident(ref value)) if value.eq_ignore_ascii_case("i") => {
             Ok(ParsedCaseSensitivity::AsciiCaseInsensitive)
         }

components/selectors/tree.rs

@@ -5,7 +5,7 @@
 //! Traits that nodes must implement. Breaks the otherwise-cyclic dependency
 //! between layout and style.
 
-use attr::{AttrSelectorOperation, NamespaceConstraint};
+use attr::{AttrSelectorOperation, NamespaceConstraint, CaseSensitivity};
 use matching::{ElementSelectorFlags, LocalMatchingContext, MatchingContext, RelevantLinkStatus};
 use parser::SelectorImpl;
 use std::fmt::Debug;
@@ -63,9 +63,20 @@ pub trait Element: Sized + Debug {
     /// Whether this element is a `link`.
     fn is_link(&self) -> bool;
 
-    fn get_id(&self) -> Option<<Self::Impl as SelectorImpl>::Identifier>;
+    /// Whether this element is in a document that is in quirks mode.
+    ///
+    /// https://dom.spec.whatwg.org/#concept-document-quirks
+    fn in_quirks_mode_document(&self) -> bool;
 
-    fn has_class(&self, name: &<Self::Impl as SelectorImpl>::ClassName) -> bool;
+    fn has_id(&self,
+              id: &<Self::Impl as SelectorImpl>::Identifier,
+              case_sensitivity: CaseSensitivity)
+              -> bool;
+
+    fn has_class(&self,
+                 name: &<Self::Impl as SelectorImpl>::ClassName,
+                 case_sensitivity: CaseSensitivity)
+                 -> bool;
 
     /// Returns whether this element matches `:empty`.
     ///