Bug 1846251 - Make CSSStyleRule inherit from CSSGroupingRule. r=peter…

…v,devtools-reviewers

As per w3c/csswg-drafts#8940.

I didn't do this in bug 1837638 because that's what the spec said at the
time, that's what other browsers did, and specially because if we did
this we had no way of runtime-disable nesting during development or if
things went south.

This means that we can't keep the nesting pref in 118, but that seems
fine (it's already enabled everywhere in 117).

Differential Revision: https://phabricator.services.mozilla.com/D184930

style/gecko/selector_parser.rs

@@ -307,8 +307,9 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
     type Impl = SelectorImpl;
     type Error = StyleParseErrorKind<'i>;
 
+    #[inline]
     fn parse_parent_selector(&self) -> bool {
-        static_prefs::pref!("layout.css.nesting.enabled")
+        true
     }
 
     #[inline]

style/stylesheets/rule_parser.rs

@@ -501,15 +501,6 @@ impl NestedParseResult {
 }
 
 impl<'a, 'i> NestedRuleParser<'a, 'i> {
-    /// When nesting is disabled, we prevent parsing at rules and qualified rules inside style
-    /// rules.
-    fn allow_at_and_qualified_rules(&self) -> bool {
-        if !self.in_style_rule() {
-            return true;
-        }
-        static_prefs::pref!("layout.css.nesting.enabled")
-    }
-
     #[inline]
     fn in_style_rule(&self) -> bool {
         self.context.rule_types.contains(CssRuleType::Style)
@@ -622,9 +613,6 @@ impl<'a, 'i> AtRuleParser<'i> for NestedRuleParser<'a, 'i> {
         name: CowRcStr<'i>,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self::Prelude, ParseError<'i>> {
-        if self.in_style_rule() && !static_prefs::pref!("layout.css.nesting.enabled") {
-            return Err(input.new_error(BasicParseErrorKind::AtRuleInvalid(name)));
-        }
         Ok(match_ignore_ascii_case! { &*name,
             "media" => {
                 let media_queries = MediaList::parse(&self.context, input);
@@ -934,9 +922,7 @@ impl<'a, 'i> DeclarationParser<'i> for NestedRuleParser<'a, 'i> {
 }
 
 impl<'a, 'i> RuleBodyItemParser<'i, (), StyleParseErrorKind<'i>> for NestedRuleParser<'a, 'i> {
-    fn parse_qualified(&self) -> bool {
-        self.allow_at_and_qualified_rules()
-    }
+    fn parse_qualified(&self) -> bool { true }
 
     /// If nesting is disabled, we can't get there for a non-style-rule. If it's enabled, we parse
     /// raw declarations there.