From b9b8ddafdea286c5ed26abb04b966c77fdfa6d17 Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Tue, 10 Dec 2024 10:56:33 +1100
Subject: [PATCH 1/2] hashes: Add lint return_self_must_use

Add the lint. No additional clippy warnings are introduced.
---
 hashes/src/lib.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hashes/src/lib.rs b/hashes/src/lib.rs
index 44b13523d..920ce9973 100644
--- a/hashes/src/lib.rs
+++ b/hashes/src/lib.rs
@@ -58,6 +58,8 @@
 #![warn(missing_docs)]
 #![warn(deprecated_in_future)]
 #![doc(test(attr(warn(unused))))]
+// Pedantic lints that we enforce.
+#![warn(clippy::return_self_not_must_use)]
 // Instead of littering the codebase for non-fuzzing and bench code just globally allow.
 #![cfg_attr(hashes_fuzz, allow(dead_code, unused_imports))]
 #![cfg_attr(bench, allow(dead_code, unused_imports))]

From f4b9c06c8bdffccfe997135f7b6ec168978e9bcc Mon Sep 17 00:00:00 2001
From: "Tobin C. Harding" <me@tobin.cc>
Date: Mon, 9 Dec 2024 17:05:27 +1100
Subject: [PATCH 2/2] hashes: Add additional must_use

Run the linter with `must_use_candidate` enabled and check all the
warnings.
---
 hashes/src/sha256.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hashes/src/sha256.rs b/hashes/src/sha256.rs
index 98e8ec132..8770b332b 100644
--- a/hashes/src/sha256.rs
+++ b/hashes/src/sha256.rs
@@ -135,6 +135,7 @@ impl crate::HashEngine for HashEngine {
 
 impl Hash {
     /// Iterate the sha256 algorithm to turn a sha256 hash into a sha256d hash
+    #[must_use]
     pub fn hash_again(&self) -> sha256d::Hash {
         crate::Hash::from_byte_array(<Self as crate::GeneralHash>::hash(&self.0).0)
     }
@@ -202,6 +203,7 @@ impl Midstate {
     ///
     /// Computes non-finalized hash of `sha256(tag) || sha256(tag)` for use in [`sha256t`]. It's
     /// provided for use with [`sha256t`].
+    #[must_use]
     pub const fn hash_tag(tag: &[u8]) -> Self {
         let hash = Hash::hash_unoptimized(tag);
         let mut buf = [0u8; 64];