Parse pseudo selector arguments as declaration values. (#2304)

Closes #2120

doc-src/SASS_CHANGELOG.md

@@ -48,6 +48,10 @@
   previously parsed as strings, and in 3.6 they will be parsed as colors
   instead.
 
+* Pseudo selectors that take arguments now allow any
+  [`<declaration-value>`][declaration-value] production in their argument list.
+  This will provide better forwards-compatibility for future CSS syntax.
+
 [hex alpha spec]: https://drafts.csswg.org/css-color/#hex-notation
 [directional focus spec]: https://www.w3.org/TR/css-ui-3/#nav-dir
 

lib/sass/scss/parser.rb

@@ -1155,7 +1155,7 @@ def merge(arr)
         :media_expr => "media expression (e.g. (min-device-width: 800px))",
         :at_root_query => "@at-root query (e.g. (without: media))",
         :at_root_directive_list => '* or identifier',
-        :pseudo_args => "expression (e.g. fr, 2n+1)",
+        :declaration_value => "expression (e.g. fr, 2n+1)",
         :interp_ident => "identifier",
         :qualified_name => "identifier",
         :expr => "expression (e.g. 1px, bold)",

lib/sass/scss/static_parser.rb

@@ -282,37 +282,14 @@ def pseudo
           elsif s == ':' && PREFIXED_SELECTOR_PSEUDO_CLASSES.include?(deprefixed)
             arg, sel = prefixed_selector_pseudo
           else
-            arg = expr!(:pseudo_args)
+            arg = expr!(:declaration_value).join
           end
 
           tok!(/\)/)
         end
         Selector::Pseudo.new(s == ':' ? :class : :element, name, arg, sel)
       end
 
-      def pseudo_args
-        arg = expr!(:pseudo_expr)
-        while tok(/,/)
-          arg << ',' << str {ss}
-          arg.concat expr!(:pseudo_expr)
-        end
-        arg
-      end
-
-      def pseudo_expr
-        res = pseudo_expr_token
-        return unless res
-        res << str {ss}
-        while (e = pseudo_expr_token)
-          res << e << str {ss}
-        end
-        res
-      end
-
-      def pseudo_expr_token
-        tok(PLUS) || tok(/[-*]/) || tok(NUMBER) || tok(STRING) || tok(IDENT)
-      end
-
       def prefixed_selector_pseudo
         prefix = str do
           expr = str {expr!(:a_n_plus_b)}