Metadata V16: Be more dynamic over which hasher is used. (#1974)

* Use DynamicHasher256 to support Blake2 or Keccack depending on chain

* remove Config::Hash associated type, replace with HashFor<Config> alias

* Fix doc links

* fix wasm tests

* Don't strip system pallet associated types. check System.Hashing, not Hash. Rename BlockHash trait to Hash

* Tweak comment

* fmt

* fix merge

* Fix typo

core/src/config/mod.rs

@@ -20,6 +20,7 @@ use core::fmt::Debug;
 use scale_decode::DecodeAsType;
 use scale_encode::EncodeAsType;
 use serde::{de::DeserializeOwned, Serialize};
+use subxt_metadata::Metadata;
 
 pub use default_extrinsic_params::{DefaultExtrinsicParams, DefaultExtrinsicParamsBuilder};
 pub use extrinsic_params::{ExtrinsicParams, ExtrinsicParamsEncoder};
@@ -33,9 +34,6 @@ pub use transaction_extensions::TransactionExtension;
 // And we want the compiler to infer `Send` and `Sync` OK for things which have `T: Config`
 // rather than having to `unsafe impl` them ourselves.
 pub trait Config: Sized + Send + Sync + 'static {
-    /// The output of the `Hasher` function.
-    type Hash: BlockHash;
-
     /// The account ID type.
     type AccountId: Debug + Clone + Encode + Decode + Serialize + Send;
 
@@ -46,7 +44,7 @@ pub trait Config: Sized + Send + Sync + 'static {
     type Signature: Debug + Clone + Encode + Decode + Send;
 
     /// The hashing system (algorithm) being used in the runtime (e.g. Blake2).
-    type Hasher: Debug + Hasher<Output = Self::Hash>;
+    type Hasher: Debug + Clone + Copy + Hasher + Send + Sync;
 
     /// The block header.
     type Header: Debug + Header<Hasher = Self::Hasher> + Sync + Send + DeserializeOwned;
@@ -58,11 +56,14 @@ pub trait Config: Sized + Send + Sync + 'static {
     type AssetId: Debug + Clone + Encode + DecodeAsType + EncodeAsType + Send;
 }
 
+/// Given some [`Config`], this returns the type of hash used.
+pub type HashFor<T> = <<T as Config>::Hasher as Hasher>::Output;
+
 /// given some [`Config`], this return the other params needed for its `ExtrinsicParams`.
 pub type ParamsFor<T> = <<T as Config>::ExtrinsicParams as ExtrinsicParams<T>>::Params;
 
 /// Block hashes must conform to a bunch of things to be used in Subxt.
-pub trait BlockHash:
+pub trait Hash:
     Debug
     + Copy
     + Send
@@ -77,7 +78,7 @@ pub trait BlockHash:
     + core::hash::Hash
 {
 }
-impl<T> BlockHash for T where
+impl<T> Hash for T where
     T: Debug
         + Copy
         + Send
@@ -97,15 +98,18 @@ impl<T> BlockHash for T where
 /// and extrinsics.
 pub trait Hasher {
     /// The type given back from the hash operation
-    type Output;
+    type Output: Hash;
+
+    /// Construct a new hasher.
+    fn new(metadata: &Metadata) -> Self;
 
     /// Hash some bytes to the given output type.
-    fn hash(s: &[u8]) -> Self::Output;
+    fn hash(&self, s: &[u8]) -> Self::Output;
 
     /// Hash some SCALE encodable type to the given output type.
-    fn hash_of<S: Encode>(s: &S) -> Self::Output {
+    fn hash_of<S: Encode>(&self, s: &S) -> Self::Output {
         let out = s.encode();
-        Self::hash(&out)
+        self.hash(&out)
     }
 }
 
@@ -120,7 +124,7 @@ pub trait Header: Sized + Encode + Decode {
     fn number(&self) -> Self::Number;
 
     /// Hash this header.
-    fn hash(&self) -> <Self::Hasher as Hasher>::Output {
-        Self::Hasher::hash_of(self)
+    fn hash_with(&self, hasher: Self::Hasher) -> <Self::Hasher as Hasher>::Output {
+        hasher.hash_of(self)
     }
 }