rand_core: add blanket impl of TryRngCore for RngCore (#1499)

This PR removes the hacky `impl_try_rng_from_rng_core` and
`impl_try_crypto_rng_from_crypto_rng` macros and replaces them with
blanket impls of `TryRngCore` for `RngCore` and `TryCryptoRng` for
`CryptoRng`.

This change means that `TryRngCore`/`TryCryptoRng` no longer can have
blanket impls for `&mut R` and `Box<R>`. But I think it should be
tolerable since most users will be using `RngCore`/`CryptoRng`, which
have blanket impl for `DerefMut` (it covers both `&mut R` and `Box<R>`).

Author: newpavlov

benches/benches/seq_choose.rs

@@ -20,7 +20,7 @@ criterion_main!(benches);
 
 pub fn bench(c: &mut Criterion) {
     c.bench_function("seq_slice_choose_1_of_100", |b| {
-        let mut rng = Pcg32::from_rng(thread_rng());
+        let mut rng = Pcg32::from_rng(&mut thread_rng());
         let mut buf = [0i32; 100];
         rng.fill(&mut buf);
         let x = black_box(&mut buf);
@@ -32,7 +32,7 @@ pub fn bench(c: &mut Criterion) {
     for (amount, len) in lens {
         let name = format!("seq_slice_choose_multiple_{}_of_{}", amount, len);
         c.bench_function(name.as_str(), |b| {
-            let mut rng = Pcg32::from_rng(thread_rng());
+            let mut rng = Pcg32::from_rng(&mut thread_rng());
             let mut buf = [0i32; 1000];
             rng.fill(&mut buf);
             let x = black_box(&buf[..len]);
@@ -53,15 +53,15 @@ pub fn bench(c: &mut Criterion) {
     }
 
     c.bench_function("seq_iter_choose_multiple_10_of_100", |b| {
-        let mut rng = Pcg32::from_rng(thread_rng());
+        let mut rng = Pcg32::from_rng(&mut thread_rng());
         let mut buf = [0i32; 100];
         rng.fill(&mut buf);
         let x = black_box(&buf);
         b.iter(|| x.iter().cloned().choose_multiple(&mut rng, 10))
     });
 
     c.bench_function("seq_iter_choose_multiple_fill_10_of_100", |b| {
-        let mut rng = Pcg32::from_rng(thread_rng());
+        let mut rng = Pcg32::from_rng(&mut thread_rng());
         let mut buf = [0i32; 100];
         rng.fill(&mut buf);
         let x = black_box(&buf);

benches/benches/shuffle.rs

@@ -20,7 +20,7 @@ criterion_main!(benches);
 
 pub fn bench(c: &mut Criterion) {
     c.bench_function("seq_shuffle_100", |b| {
-        let mut rng = Pcg32::from_rng(thread_rng());
+        let mut rng = Pcg32::from_rng(&mut thread_rng());
         let mut buf = [0i32; 100];
         rng.fill(&mut buf);
         let x = black_box(&mut buf);

benches/benches/uniform.rs

@@ -23,7 +23,7 @@ const N_RESAMPLES: usize = 10_000;
 macro_rules! sample {
     ($R:ty, $T:ty, $U:ty, $g:expr) => {
         $g.bench_function(BenchmarkId::new(stringify!($R), "single"), |b| {
-            let mut rng = <$R>::from_rng(thread_rng());
+            let mut rng = <$R>::from_rng(&mut thread_rng());
             let x = rng.random::<$U>();
             let bits = (<$T>::BITS / 2);
             let mask = (1 as $U).wrapping_neg() >> bits;
@@ -35,7 +35,7 @@ macro_rules! sample {
         });
 
         $g.bench_function(BenchmarkId::new(stringify!($R), "distr"), |b| {
-            let mut rng = <$R>::from_rng(thread_rng());
+            let mut rng = <$R>::from_rng(&mut thread_rng());
             let x = rng.random::<$U>();
             let bits = (<$T>::BITS / 2);
             let mask = (1 as $U).wrapping_neg() >> bits;

benches/benches/uniform_float.rs

@@ -27,7 +27,7 @@ const N_RESAMPLES: usize = 10_000;
 macro_rules! single_random {
     ($R:ty, $T:ty, $g:expr) => {
         $g.bench_function(BenchmarkId::new(stringify!($T), stringify!($R)), |b| {
-            let mut rng = <$R>::from_rng(thread_rng());
+            let mut rng = <$R>::from_rng(&mut thread_rng());
             let (mut low, mut high);
             loop {
                 low = <$T>::from_bits(rng.random());
@@ -63,7 +63,7 @@ fn single_random(c: &mut Criterion) {
 macro_rules! distr_random {
     ($R:ty, $T:ty, $g:expr) => {
         $g.bench_function(BenchmarkId::new(stringify!($T), stringify!($R)), |b| {
-            let mut rng = <$R>::from_rng(thread_rng());
+            let mut rng = <$R>::from_rng(&mut thread_rng());
             let dist = loop {
                 let low = <$T>::from_bits(rng.random());
                 let high = <$T>::from_bits(rng.random());

benches/benches/weighted.rs

@@ -53,7 +53,7 @@ pub fn bench(c: &mut Criterion) {
         c.bench_function(name.as_str(), |b| {
             let length = black_box(length);
             let amount = black_box(amount);
-            let mut rng = SmallRng::from_rng(thread_rng());
+            let mut rng = SmallRng::from_rng(&mut thread_rng());
             b.iter(|| sample_weighted(&mut rng, length, |idx| (1 + (idx % 100)) as u32, amount))
         });
     }

rand_chacha/src/chacha.rs

@@ -257,8 +257,6 @@ macro_rules! chacha_impl {
 
         impl CryptoRng for $ChaChaXRng {}
 
-        rand_core::impl_try_crypto_rng_from_crypto_rng!($ChaChaXRng);
-
         impl From<$ChaChaXCore> for $ChaChaXRng {
             fn from(core: $ChaChaXCore) -> Self {
                 $ChaChaXRng {

rand_core/src/blanket_impls.rs

@@ -250,12 +250,12 @@ impl<R: BlockRngCore + SeedableRng> SeedableRng for BlockRng<R> {
     }
 
     #[inline(always)]
-    fn from_rng(rng: impl RngCore) -> Self {
+    fn from_rng(rng: &mut impl RngCore) -> Self {
         Self::new(R::from_rng(rng))
     }
 
     #[inline(always)]
-    fn try_from_rng<S: TryRngCore>(rng: S) -> Result<Self, S::Error> {
+    fn try_from_rng<S: TryRngCore>(rng: &mut S) -> Result<Self, S::Error> {
         R::try_from_rng(rng).map(Self::new)
     }
 }
@@ -415,12 +415,12 @@ impl<R: BlockRngCore + SeedableRng> SeedableRng for BlockRng64<R> {
     }
 
     #[inline(always)]
-    fn from_rng(rng: impl RngCore) -> Self {
+    fn from_rng(rng: &mut impl RngCore) -> Self {
         Self::new(R::from_rng(rng))
     }
 
     #[inline(always)]
-    fn try_from_rng<S: TryRngCore>(rng: S) -> Result<Self, S::Error> {
+    fn try_from_rng<S: TryRngCore>(rng: &mut S) -> Result<Self, S::Error> {
         R::try_from_rng(rng).map(Self::new)
     }
 }

rand_core/src/block.rs

@@ -160,60 +160,6 @@ pub fn next_u64_via_fill<R: RngCore + ?Sized>(rng: &mut R) -> u64 {
     u64::from_le_bytes(buf)
 }
 
-/// Implement [`TryRngCore`][crate::TryRngCore] for a type implementing [`RngCore`].
-///
-/// Ideally, `rand_core` would define blanket impls for this, but they conflict with blanket impls
-/// for `&mut R` and `Box<R>`, so until specialziation is stabilized, implementer crates
-/// have to implement `TryRngCore` directly.
-#[macro_export]
-macro_rules! impl_try_rng_from_rng_core {
-    ($t:ty) => {
-        impl $crate::TryRngCore for $t {
-            type Error = core::convert::Infallible;
-
-            #[inline]
-            fn try_next_u32(&mut self) -> Result<u32, Self::Error> {
-                Ok($crate::RngCore::next_u32(self))
-            }
-
-            #[inline]
-            fn try_next_u64(&mut self) -> Result<u64, Self::Error> {
-                Ok($crate::RngCore::next_u64(self))
-            }
-
-            #[inline]
-            fn try_fill_bytes(&mut self, dst: &mut [u8]) -> Result<(), Self::Error> {
-                $crate::RngCore::fill_bytes(self, dst);
-                Ok(())
-            }
-        }
-    };
-}
-
-/// Implement [`TryCryptoRng`] and [`TryRngCore`] for a type implementing [`CryptoRng`].
-///
-/// Ideally, `rand_core` would define blanket impls for this, but they conflict with blanket impls
-/// for `&mut R` and `Box<R>`, so until specialziation is stabilized, implementer crates
-/// have to implement `TryRngCore` and `TryCryptoRng` directly.
-///
-/// [`TryCryptoRng`]: crate::TryCryptoRng
-/// [`TryRngCore`]: crate::TryRngCore
-/// [`CryptoRng`]: crate::CryptoRng
-#[macro_export]
-macro_rules! impl_try_crypto_rng_from_crypto_rng {
-    ($t:ty) => {
-        $crate::impl_try_rng_from_rng_core!($t);
-
-        impl $crate::TryCryptoRng for $t {}
-
-        /// Check at compile time that `$t` implements `CryptoRng`
-        const _: () = {
-            const fn check_crypto_rng_impl<T: $crate::CryptoRng>() {}
-            check_crypto_rng_impl::<$t>();
-        };
-    };
-}
-
 #[cfg(test)]
 mod test {
     use super::*;