Improve performance

Author: GuillaumeGomez

src/librustdoc/html/highlight.rs

@@ -7,8 +7,9 @@
 
 use std::collections::VecDeque;
 use std::fmt::{self, Display, Write};
-use std::{cmp, iter};
+use std::iter;
 
+use itertools::Either;
 use rustc_data_structures::fx::FxIndexMap;
 use rustc_lexer::{Cursor, FrontmatterAllowed, LiteralKind, TokenKind};
 use rustc_span::BytePos;
@@ -168,8 +169,11 @@ impl Element {
         let mut prev = parent_class;
         let mut closing_tag = None;
         for part in &self.content {
-            let text: &dyn Display =
-                if part.needs_escape { &EscapeBodyText(&part.text) } else { &part.text };
+            let text = if part.needs_escape {
+                Either::Left(&EscapeBodyText(&part.text))
+            } else {
+                Either::Right(&part.text)
+            };
             if part.class.is_some() {
                 // We only try to generate links as the `<span>` should have already be generated
                 // by the caller of `write_elem_to`.
@@ -236,9 +240,7 @@ impl ElementStack {
         if let Some(ElementOrStack::Element(last)) = self.elements.last_mut()
             && last.can_merge(&elem)
         {
-            for part in elem.content.drain(..) {
-                last.content.push(part);
-            }
+            last.content.append(&mut elem.content);
         } else {
             self.elements.push(ElementOrStack::Element(elem));
         }
@@ -262,9 +264,7 @@ impl ElementStack {
         if self.pending_exit {
             if can_merge(self.class, class, "") {
                 self.pending_exit = false;
-                for elem in elements {
-                    self.elements.push(elem);
-                }
+                self.elements.extend(elements);
                 // Compatible stacks, nothing to be done here!
                 return;
             }