box attribute selector, significantly reducing the size of the simple selector enum

src/selector/parse.rs

@@ -264,9 +264,9 @@ impl<'a, 'b> SelectorParser<'a, 'b> {
 
     fn parse_attribute_selector(&mut self) -> SassResult<SimpleSelector> {
         self.parser.toks.next();
-        Ok(SimpleSelector::Attribute(Attribute::from_tokens(
+        Ok(SimpleSelector::Attribute(Box::new(Attribute::from_tokens(
             self.parser,
-        )?))
+        )?)))
     }
 
     fn parse_class_selector(&mut self) -> SassResult<SimpleSelector> {

src/selector/simple.rs

@@ -62,7 +62,7 @@ pub(crate) enum SimpleSelector {
     /// the given name.
     Class(String),
 
-    Attribute(Attribute),
+    Attribute(Box<Attribute>),
 }
 
 impl fmt::Display for SimpleSelector {