_hashlib.HMAC and Update hmac from v3.14.3 - #7159

Walkthrough

RustPython's hashlib module now supports HMAC operations through a type-erased dispatch pattern. The changes introduce a new PyHmac class wrapping algorithm metadata and a thread-safe context implementing standard HMAC methods (update, digest, hexdigest, copy). The implementation uses a DynHmac trait with TypedHmac<D> concrete wrappers to handle multiple hash algorithms uniformly.

Changes

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Possibly related PRs

• Update hashlib from v3.14.3 and align _hashlib to CPython #7120: Modifies the same crates/stdlib/src/hashlib.rs file to add/implement HMAC support with overlapping changes on hmac_new, resolve_digestmod, and HMAC creation/dispatch logic.

Poem

🐰 Hops through HMAC traits with glee,
Type erasure set our messages free,
DynHmac bounces, TypedHmac springs,
Secure digests on cryptographic wings! ✨

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

• 📝 Generate docstrings

crates/stdlib/src/hashlib.rs (1)

261-285: Consider using DynClone for consistency with ThreadSafeDynDigest.

The file already imports dyn_clone::{DynClone, clone_trait_object} (line 24) and uses them for ThreadSafeDynDigest (line 876). DynHmac manually re-implements the same pattern with dyn_clone(). Unifying on the crate-provided mechanism removes boilerplate and keeps the two trait-object hierarchies consistent.

♻️ Suggested refactor

-    trait DynHmac: Send + Sync {
+    trait DynHmac: DynClone + Send + Sync {
         fn dyn_update(&mut self, data: &[u8]);
         fn dyn_finalize(&self) -> Vec<u8>;
-        fn dyn_clone(&self) -> Box<dyn DynHmac>;
     }
+    clone_trait_object!(DynHmac);
 
     struct TypedHmac<D>(D);
 
     impl<D> DynHmac for TypedHmac<D>
     where
         D: Mac + Clone + Send + Sync + 'static,
     {
         fn dyn_update(&mut self, data: &[u8]) {
             Mac::update(&mut self.0, data);
         }
 
         fn dyn_finalize(&self) -> Vec<u8> {
             self.0.clone().finalize().into_bytes().to_vec()
         }
-
-        fn dyn_clone(&self) -> Box<dyn DynHmac> {
-            Box::new(TypedHmac(self.0.clone()))
-        }
     }

Then in PyHmac::copy (line 346), replace self.ctx.read().dyn_clone() with self.ctx.read().clone() (which clone_trait_object! provides for Box<dyn DynHmac>).

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