allow whitespace between @content and its args

src/parse/mixin.rs

@@ -213,6 +213,8 @@ impl<'a> Parser<'a> {
 
             let mut entered_scope = false;
 
+            self.whitespace_or_comment();
+
             let call_args = if self.consume_char_if_exists('(') {
                 self.parse_call_args()?
             } else {

tests/mixins.rs

@@ -538,6 +538,20 @@ test!(
     }",
     "a {\n  color: red;\n}\n"
 );
+test!(
+    space_between_content_and_args,
+    "space-after-content {
+        @mixin mixin {
+            @content /**/ (value1, value2);
+        }
+
+        @include mixin using ($arg1, $arg2) {
+            arg1: $arg1;
+            arg2: $arg2;
+        }
+    }",
+    "space-after-content {\n  arg1: value1;\n  arg2: value2;\n}\n"
+);
 error!(
     mixin_in_function,
     "@function foo() {