Reduce usage of Blake2Hasher (#5132)

This reduces the usage of `Blake2Hasher` in the code base and replaces
it with `BlakeTwo256`. The most important change is the removal of the
custom extern function for `Blake2Hasher`. The runtime `Hash` trait is
now also simplified and directly requires that the implementing type
implements `Hashable`.

substrate/primitives/runtime/src/random_number_generator.rs

@@ -66,7 +66,7 @@ impl<Hashing: Hash> RandomNumberGenerator<Hashing> {
 		loop {
 			if self.offset() + needed > self.current.as_ref().len() {
 				// rehash
-				self.current = Hashing::hash(self.current.as_ref());
+				self.current = <Hashing as Hash>::hash(self.current.as_ref());
 				self.offset = 0;
 			}
 			let data = &self.current.as_ref()[self.offset()..self.offset() + needed];

substrate/primitives/runtime/src/traits.rs

@@ -25,7 +25,7 @@ use std::fmt::Display;
 use std::str::FromStr;
 #[cfg(feature = "std")]
 use serde::{Serialize, Deserialize, de::DeserializeOwned};
-use sp_core::{self, Hasher, Blake2Hasher, TypeId, RuntimeDebug};
+use sp_core::{self, Hasher, TypeId, RuntimeDebug};
 use crate::codec::{Codec, Encode, Decode};
 use crate::transaction_validity::{
 	ValidTransaction, TransactionValidity, TransactionValidityError, UnknownTransaction,
@@ -369,20 +369,19 @@ pub trait OffchainWorker<BlockNumber> {
 /// Abstraction around hashing
 // Stupid bug in the Rust compiler believes derived
 // traits must be fulfilled by all type parameters.
-pub trait Hash: 'static + MaybeSerializeDeserialize + Debug + Clone + Eq + PartialEq {
+pub trait Hash: 'static + MaybeSerializeDeserialize + Debug + Clone + Eq + PartialEq + Hasher<Out = <Self as Hash>::Output> {
 	/// The hash type produced.
 	type Output: Member + MaybeSerializeDeserialize + Debug + sp_std::hash::Hash
 		+ AsRef<[u8]> + AsMut<[u8]> + Copy + Default + Encode + Decode;
 
-	/// The associated hash_db Hasher type.
-	type Hasher: Hasher<Out=Self::Output>;
-
 	/// Produce the hash of some byte-slice.
-	fn hash(s: &[u8]) -> Self::Output;
+	fn hash(s: &[u8]) -> Self::Output {
+		<Self as Hasher>::hash(s)
+	}
 
 	/// Produce the hash of some codec-encodable value.
 	fn hash_of<S: Encode>(s: &S) -> Self::Output {
-		Encode::using_encoded(s, Self::hash)
+		Encode::using_encoded(s, <Self as Hasher>::hash)
 	}
 
 	/// The ordered Patricia tree root of the given `input`.
@@ -397,12 +396,18 @@ pub trait Hash: 'static + MaybeSerializeDeserialize + Debug + Clone + Eq + Parti
 #[cfg_attr(feature = "std", derive(Serialize, Deserialize))]
 pub struct BlakeTwo256;
 
-impl Hash for BlakeTwo256 {
-	type Output = sp_core::H256;
-	type Hasher = Blake2Hasher;
-	fn hash(s: &[u8]) -> Self::Output {
+impl Hasher for BlakeTwo256 {
+	type Out = sp_core::H256;
+	type StdHasher = hash256_std_hasher::Hash256StdHasher;
+	const LENGTH: usize = 32;
+
+	fn hash(s: &[u8]) -> Self::Out {
 		sp_io::hashing::blake2_256(s).into()
 	}
+}
+
+impl Hash for BlakeTwo256 {
+	type Output = sp_core::H256;
 
 	fn trie_root(input: Vec<(Vec<u8>, Vec<u8>)>) -> Self::Output {
 		sp_io::trie::blake2_256_root(input)
@@ -616,8 +621,6 @@ pub trait ExtrinsicMetadata {
 	type SignedExtensions: SignedExtension;
 }
 
-/// Extract the hasher type for a block.
-pub type HasherFor<B> = <HashFor<B> as Hash>::Hasher;
 /// Extract the hashing type for a block.
 pub type HashFor<B> = <<B as Block>::Header as Header>::Hashing;
 /// Extract the number type for a block.