From ae3a5153377f2271ba7dfe686a9b5bca1632c32b Mon Sep 17 00:00:00 2001
From: Konrad Borowski <konrad@borowski.pw>
Date: Mon, 18 Jan 2021 17:56:06 +0100
Subject: [PATCH] Avoid hash_slice in VecDeque's Hash implementation
Fixes #80303.
---
.../alloc/src/collections/vec_deque/mod.rs | 10 +++--
.../alloc/src/collections/vec_deque/tests.rs | 40 +++++++++++++++++++
2 files changed, 47 insertions(+), 3 deletions(-)
diff --git a/library/alloc/src/collections/vec_deque/mod.rs b/library/alloc/src/collections/vec_deque/mod.rs
index 5b61e8911a59a..6f9133e2811bf 100644
--- a/library/alloc/src/collections/vec_deque/mod.rs
+++ b/library/alloc/src/collections/vec_deque/mod.rs
@@ -2646,9 +2646,13 @@ impl<A: Ord> Ord for VecDeque<A> {
impl<A: Hash> Hash for VecDeque<A> {
fn hash<H: Hasher>(&self, state: &mut H) {
self.len().hash(state);
- let (a, b) = self.as_slices();
- Hash::hash_slice(a, state);
- Hash::hash_slice(b, state);
+ // It's not possible to use Hash::hash_slice on slices
+ // returned by as_slices method as their length can vary
+ // in otherwise identical deques.
+ //
+ // Hasher only guarantees equivalence for the exact same
+ // set of calls to its methods.
+ self.iter().for_each(|elem| elem.hash(state));
}
}
diff --git a/library/alloc/src/collections/vec_deque/tests.rs b/library/alloc/src/collections/vec_deque/tests.rs
index 27dc59ae64411..87e06fa394d38 100644
--- a/library/alloc/src/collections/vec_deque/tests.rs
+++ b/library/alloc/src/collections/vec_deque/tests.rs
@@ -599,3 +599,43 @@ fn issue_53529() {
assert_eq!(*a, 2);
}
}
+
+#[test]
+fn issue_80303() {
+ use core::iter;
+ use core::num::Wrapping;
+
+ // This is a valid, albeit rather bad hash function implementation.
+ struct SimpleHasher(Wrapping<u64>);
+
+ impl Hasher for SimpleHasher {
+ fn finish(&self) -> u64 {
+ self.0.0
+ }
+
+ fn write(&mut self, bytes: &[u8]) {
+ // This particular implementation hashes value 24 in addition to bytes.
+ // Such an implementation is valid as Hasher only guarantees equivalence
+ // for the exact same set of calls to its methods.
+ for &v in iter::once(&24).chain(bytes) {
+ self.0 = Wrapping(31) * self.0 + Wrapping(u64::from(v));
+ }
+ }
+ }
+
+ fn hash_code(value: impl Hash) -> u64 {
+ let mut hasher = SimpleHasher(Wrapping(1));
+ value.hash(&mut hasher);
+ hasher.finish()
+ }
+
+ // This creates two deques for which values returned by as_slices
+ // method differ.
+ let vda: VecDeque<u8> = (0..10).collect();
+ let mut vdb = VecDeque::with_capacity(10);
+ vdb.extend(5..10);
+ (0..5).rev().for_each(|elem| vdb.push_front(elem));
+ assert_ne!(vda.as_slices(), vdb.as_slices());
+ assert_eq!(vda, vdb);
+ assert_eq!(hash_code(vda), hash_code(vdb));
+}