hashes: silence new `unused-assignments` clippy lint
What the developer wrote
Authored by Andrew Poelstra
hashes: silence new `unused-assignments` clippy lint
In our `round!` macro invocation for the implementation for sha256 and
sha512 we do an assignment of a variable `$w` which is fed into the next
round. On the last round, this assignment is unused, which makes clippy
unhappy on recent nightlies.
Fix this so we can update our nightly compiler.
What changed, and why it matters
This commit is a code-quality cleanup, not a security fix. It adds a `let _ = w[15];` line in two SHA hashing implementation files solely to silence a new Rust clippy lint about an unused assignment inside a macro on the final round of SHA-256 and SHA-512. The generated machine code and behavior are unchanged.
No security action needed; treat as a normal lint-silencing cleanup.
Security signals we found
No strong security signals were identified.
Evidence from the diff
The change suppresses the unused-assignments/unnecessary assignment clippy lint that appears on recent nightly compilers. The round! macro assigns to $w, and on the last invocation that assignment is never read. Adding let _ = w[15]; makes the compiler consider the value used, without affecting logic or generated code. No cryptographic constants, operations, or control flow are modified.
Changed components
hashes/src/sha256/crypto.rshashes/src/sha512/crypto.rsInspect captured patch +2 / −0
diff --git a/hashes/src/sha256/crypto.rs b/hashes/src/sha256/crypto.rs
index f85e0ec9..905a5848 100644
--- a/hashes/src/sha256/crypto.rs
+++ b/hashes/src/sha256/crypto.rs
@@ -608,6 +608,7 @@ impl HashEngine {
round!(d, e, f, g, h, a, b, c, 0xa4506ceb, w[13], w[11], w[6], w[14]);
round!(c, d, e, f, g, h, a, b, 0xbef9a3f7, w[14], w[12], w[7], w[15]);
round!(b, c, d, e, f, g, h, a, 0xc67178f2, w[15], w[13], w[8], w[0]);
+ let _ = w[15]; // silence "unnecessary assignment" lint in macro
self.h[0] = self.h[0].wrapping_add(a);
self.h[1] = self.h[1].wrapping_add(b);
diff --git a/hashes/src/sha512/crypto.rs b/hashes/src/sha512/crypto.rs
index 6bf4f5ce..a86d962e 100644
--- a/hashes/src/sha512/crypto.rs
+++ b/hashes/src/sha512/crypto.rs
@@ -174,6 +174,7 @@ impl HashEngine {
round!(d, e, f, g, h, a, b, c, 0x597f299cfc657e2a, w[13], w[11], w[6], w[14]);
round!(c, d, e, f, g, h, a, b, 0x5fcb6fab3ad6faec, w[14], w[12], w[7], w[15]);
round!(b, c, d, e, f, g, h, a, 0x6c44198c4a475817, w[15], w[13], w[8], w[0]);
+ let _ = w[15]; // silence "unnecessary assignment" lint in macro
self.h[0] = self.h[0].wrapping_add(a);
self.h[1] = self.h[1].wrapping_add(b);
Why this scored 15/100
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