From fc1a189d119f711dbd15f685e9c56ba91e285b26 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sun, 24 Jul 2022 21:47:35 -0700
Subject: [PATCH] Preallocate TokenBuffer vector

---
 src/buffer.rs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/buffer.rs b/src/buffer.rs
index cf280fa31d..26ff67c8d0 100644
--- a/src/buffer.rs
+++ b/src/buffer.rs
@@ -59,9 +59,10 @@ impl TokenBuffer {
     fn inner_new(stream: TokenStream, up: *const Entry) -> TokenBuffer {
         // Build up the entries list, recording the locations of any Groups
         // in the list to be processed later.
-        let mut entries = Vec::new();
+        let iterator = stream.into_iter();
+        let mut entries = Vec::with_capacity(iterator.size_hint().0 + 1);
         let mut groups = Vec::new();
-        for tt in stream {
+        for tt in iterator {
             match tt {
                 TokenTree::Ident(ident) => {
                     entries.push(Entry::Ident(ident));