From 203cba76e07c87c4e665b2e78ca0358b5a72e86a Mon Sep 17 00:00:00 2001
From: Nicholas Nethercote <n.nethercote@gmail.com>
Date: Mon, 31 Jul 2023 15:53:46 +1000
Subject: [PATCH] Only call `parse_token_tree` once.

This code currently uses a `while` loop and gathers token trees into a
vector, but it only succeeds in the case where there is a single token
tree. We can instead just call `parse_token_tree` once and then look for
`Eof` to detect the success case.
---
 src/librustdoc/clean/render_macro_matchers.rs | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/src/librustdoc/clean/render_macro_matchers.rs b/src/librustdoc/clean/render_macro_matchers.rs
index b3dc0f63e45..66d10f2368b 100644
--- a/src/librustdoc/clean/render_macro_matchers.rs
+++ b/src/librustdoc/clean/render_macro_matchers.rs
@@ -76,14 +76,13 @@ fn snippet_equal_to_token(tcx: TyCtxt<'_>, matcher: &TokenTree) -> Option<String
         };
 
     // Reparse a single token tree.
-    let mut reparsed_trees = Vec::new();
-    while parser.token != token::Eof {
-        reparsed_trees.push(parser.parse_token_tree());
-    }
-    if reparsed_trees.len() != 1 {
+    if parser.token == token::Eof {
+        return None;
+    }
+    let reparsed_tree = parser.parse_token_tree();
+    if parser.token != token::Eof {
         return None;
     }
-    let reparsed_tree = reparsed_trees.pop().unwrap();
 
     // Compare against the original tree.
     if reparsed_tree.eq_unspanned(matcher) { Some(snippet) } else { None }