From 6ca3c44af89ac5f4319a64e7c1d65824779b0a59 Mon Sep 17 00:00:00 2001
From: Mark Rousskov <mark.simulacrum@gmail.com>
Date: Fri, 19 Jan 2024 19:59:04 -0500
Subject: [PATCH] Add back str sentinels

---
 rustc-hash/src/lib.rs | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/rustc-hash/src/lib.rs b/rustc-hash/src/lib.rs
index d043182e0333e..cf5ad0da4f15f 100644
--- a/rustc-hash/src/lib.rs
+++ b/rustc-hash/src/lib.rs
@@ -165,10 +165,12 @@ impl Hasher for FxHasher {
         self.add_to_hash(i);
     }
 
-    // Avoid hashing 0xFF sentinel; we don't need prefix-free hashes.
     #[inline]
     fn write_str(&mut self, s: &str) {
         self.write(s.as_bytes());
+        // FIXME: Not having this seems to add significant cost to Symbol::intern(?), but it's not
+        // very clear why. That's interning &str, so it's not obvious why this matters.
+        self.write_u8(0xFF);
     }
 
     // Avoid hashing length prefixes. For our purposes the actual data gives us plenty of entropy