Bug 1917089: Let nested @scope rule to use relative selector in scope-start. r=firefox-style-system-reviewers,emilio

Depends on D221253

Differential Revision: https://phabricator.services.mozilla.com/D221254

servo/components/style/stylesheets/rule_parser.rs

@@ -729,7 +729,7 @@ impl<'a, 'i> AtRuleParser<'i> for NestedRuleParser<'a, 'i> {
                 AtRulePrelude::Document(cond)
             },
             "scope" if static_prefs::pref!("layout.css.at-scope.enabled") => {
-                let bounds = ScopeBounds::parse(&self.context, input, self.in_style_rule())?;
+                let bounds = ScopeBounds::parse(&self.context, input, self.parse_relative())?;
                 AtRulePrelude::Scope(bounds)
             },
             "starting-style" if static_prefs::pref!("layout.css.starting-style-at-rules.enabled") => {

servo/components/style/stylesheets/scope_rule.rs

@@ -113,7 +113,7 @@ impl ScopeBounds {
 fn parse_scope<'a>(
     context: &ParserContext,
     input: &mut Parser<'a, '_>,
-    in_style_rule: bool,
+    parse_relative: ParseRelative,
     for_end: bool,
 ) -> Result<Option<SelectorList<SelectorImpl>>, ParseError<'a>> {
     input
@@ -145,10 +145,8 @@ fn parse_scope<'a>(
                 };
                 let parse_relative = if for_end {
                     ParseRelative::ForScope
-                } else if in_style_rule {
-                    ParseRelative::ForNesting
                 } else {
-                    ParseRelative::No
+                    parse_relative
                 };
                 Ok(Some(SelectorList::parse_disallow_pseudo(
                     &selector_parser,
@@ -164,10 +162,10 @@ impl ScopeBounds {
     pub fn parse<'a>(
         context: &ParserContext,
         input: &mut Parser<'a, '_>,
-        in_style_rule: bool,
+        parse_relative: ParseRelative,
     ) -> Result<Self, ParseError<'a>> {
-        let start = parse_scope(context, input, in_style_rule, false)?;
-        let end = parse_scope(context, input, in_style_rule, true)?;
+        let start = parse_scope(context, input, parse_relative, false)?;
+        let end = parse_scope(context, input, parse_relative, true)?;
         Ok(Self { start, end })
     }
 }

testing/web-platform/tests/css/css-cascade/scope-nesting.html

@@ -542,3 +542,37 @@ test((t) => {
   assert_equals(getComputedStyle(b_inside).zIndex, '1');
 }, 'Scoped nested group rule');
 </script>
+
+<template id=test_scoped_within_scoped>
+  <div>
+    <style>
+      @scope (.a) {
+        @scope(#descendant) {
+          :scope {
+            z-index: 1;
+          }
+        }
+        @scope (> #child) {
+          :scope {
+            z-index: 1;
+          }
+        }
+      }
+    </style>
+    <div class="a">
+      <div id="descendant">
+      </div>
+      <div id="child">
+      </div>
+    </div>
+</div>
+</template>
+<script>
+test((t) => {
+  t.add_cleanup(() => main.replaceChildren());
+  main.append(test_scoped_within_scoped.content.cloneNode(true));
+
+  assert_equals(getComputedStyle(descendant).zIndex, '1');
+  assert_equals(getComputedStyle(child).zIndex, '1');
+}, 'Scoped nested within another scope');
+</script>