Fix selector splitting inside functional pseudo-classes

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Unreleased
 
+* Fix selector splitting inside functional pseudo-classes (`:is()`, `:where()`, `:not()`, etc.) — commas inside parenthesised selector lists are no longer treated as selector separators
+
 ### Version 2.0.0
 * Drop ruby <3.2, fix a memory leak
 

lib/css_parser/rule_set.rb

@@ -684,17 +684,45 @@ def unmatched_open_parenthesis?(declarations)
       (lparen_index = declarations.index(LPAREN)) && !declarations.index(RPAREN, lparen_index)
     end
 
-    #--
-    # TODO: way too simplistic
-    #++
+    # Split selector string on commas, but not commas inside parentheses
+    # (e.g. :is(rect, circle) or :where(.a, .b) should not be split).
     def parse_selectors!(selectors) # :nodoc:
-      @selectors = selectors.split(',').map do |s|
+      @selectors = split_selectors(selectors).map do |s|
         s.gsub!(/\s+/, ' ')
         s.strip!
         s
       end
     end
 
+    def split_selectors(selectors)
+      result = []
+      current = +''
+      depth = 0
+
+      selectors.each_char do |char|
+        case char
+        when '('
+          depth += 1
+          current << char
+        when ')'
+          depth -= 1
+          current << char
+        when ','
+          if depth > 0
+            current << char
+          else
+            result << current
+            current = +''
+          end
+        else
+          current << char
+        end
+      end
+
+      result << current unless current.empty?
+      result
+    end
+
     def split_value_preserving_function_whitespace(value)
       split_value = value.gsub(RE_FUNCTIONS) do |c|
         c.gsub!(/\s+/, WHITESPACE_REPLACEMENT)

test/test_rule_set.rb

@@ -96,6 +96,27 @@ def test_selector_sanitization
     assert rs.selectors.member?("h3")
   end
 
+  def test_selector_splitting_preserves_functional_pseudo_classes
+    # :is() and :where() can contain comma-separated selector lists
+    rs = RuleSet.new(selectors: ':is(rect, circle)', block: 'fill: red;')
+    assert_equal [':is(rect, circle)'], rs.selectors
+  end
+
+  def test_selector_splitting_preserves_where_pseudo_class
+    rs = RuleSet.new(selectors: ':where(.a, .b)', block: 'color: blue;')
+    assert_equal [':where(.a, .b)'], rs.selectors
+  end
+
+  def test_selector_splitting_with_functional_pseudo_class_and_other_selectors
+    rs = RuleSet.new(selectors: ':is(h1, h2, h3), .other', block: 'color: red;')
+    assert_equal [':is(h1, h2, h3)', '.other'], rs.selectors
+  end
+
+  def test_selector_splitting_with_nested_functional_pseudo_classes
+    rs = RuleSet.new(selectors: ':is(:not(.a), .b)', block: 'color: red;')
+    assert_equal [':is(:not(.a), .b)'], rs.selectors
+  end
+
   def test_multiple_selectors_to_s
     selectors = "#content p, a"
     rs = RuleSet.new(selectors: selectors, block: "color: #fff;")