less symbols interner locks

compiler/rustc_resolve/src/rustdoc.rs

@@ -167,12 +167,13 @@ pub fn unindent_doc_fragments(docs: &mut [DocFragment]) {
 ///
 /// Note: remove the trailing newline where appropriate
 pub fn add_doc_fragment(out: &mut String, frag: &DocFragment) {
-    let s = frag.doc.as_str();
-    let mut iter = s.lines();
-    if s.is_empty() {
+    if frag.doc == kw::Empty {
         out.push('\n');
         return;
     }
+    let s = frag.doc.as_str();
+    let mut iter = s.lines();
+
     while let Some(line) = iter.next() {
         if line.chars().any(|c| !c.is_whitespace()) {
             assert!(line.len() >= frag.indent);