relax Sized requirements on rng

Author: baloo

CHANGELOG.md

@@ -10,6 +10,9 @@ and this library adheres to Rust's notion of
 ### Changed
 - MSRV is now 1.63.0.
 - Migrated to `rand_core 0.9`.
+- `ff::Field::random(rng: impl RngCore) -> Self` has been changed back to
+  `Field::random<R: RngCore + ?Sized>(rng: &mut R) -> Self`, to enable passing a
+  trait object as the RNG.
 
 ### Removed
 - `derive_bits` feature flag (use `bits` instead).

ff_derive/src/lib.rs

@@ -1267,7 +1267,7 @@ fn prime_field_impl(
             const ONE: Self = R;
 
             /// Computes a uniformly random element using rejection sampling.
-            fn random(mut rng: impl ::ff::derive::rand_core::RngCore) -> Self {
+            fn random<R: ::ff::derive::rand_core::RngCore + ?Sized>(rng: &mut R) -> Self {
                 loop {
                     let mut tmp = {
                         let mut repr = [0u64; #limbs];

src/lib.rs

@@ -75,7 +75,7 @@ pub trait Field:
     const ONE: Self;
 
     /// Returns an element chosen uniformly at random using a user-provided RNG.
-    fn random(rng: impl RngCore) -> Self;
+    fn random<R: RngCore + ?Sized>(rng: &mut R) -> Self;
 
     /// Returns true iff this element is zero.
     fn is_zero(&self) -> Choice {

tests/derive.rs

@@ -32,7 +32,7 @@ mod full_limbs {
     fn random_masking_does_not_overflow() {
         use ff::Field;
 
-        let _ = F384p::random(rand::rng());
+        let _ = F384p::random(&mut rand::rng());
     }
 }