optimize double map first key hash (#2451)

* fix double map encoding it is now encoded as specified in the doc

substrate/srml/support/procedural/src/lib.rs

@@ -54,7 +54,7 @@ use proc_macro::TokenStream;
 ///
 ///   `hasher($hash)` is optional and its default is `blake2_256`.
 ///
-///   /!\ Be careful with each key in the map that is inserted in the trie `$hash(module_name ++ storage_name ++ key)`.
+///   /!\ Be careful with each key in the map that is inserted in the trie `$hash(module_name ++ " " ++ storage_name ++ encoding(key))`.
 ///   If the keys are not trusted (e.g. can be set by a user), a cryptographic `hasher` such as
 ///   `blake2_256` must be used. Otherwise, other values in storage can be compromised.
 ///
@@ -71,7 +71,7 @@ use proc_macro::TokenStream;
 ///   The final key is calculated as follows:
 ///
 ///   ```nocompile
-///   $hash(module_name ++ storage_name ++ first_key) ++ $hash2(second_key)
+///   $hash(module_name ++ " " ++ storage_name ++ encoding(first_key)) ++ $hash2(encoding(second_key))
 ///   ```
 ///
 ///   If the first key is untrusted, a cryptographic `hasher` such as `blake2_256` must be used.

substrate/srml/support/procedural/src/storage/impls.rs

@@ -621,9 +621,11 @@ impl<'a, I: Iterator<Item=syn::Meta>> Impls<'a, I> {
 				type Query = #value_type;
 
 				fn prefix_for(k1: &#k1ty) -> Vec<u8> {
+					use #scrate::storage::hashed::generator::StorageHasher;
+
 					let mut key = #as_double_map::prefix().to_vec();
 					#scrate::codec::Encode::encode_to(k1, &mut key);
-					#scrate::Hashable::#hasher(&key).to_vec()
+					#scrate::#hasher::hash(&key[..]).to_vec()
 				}
 
 				fn prefix() -> &'static [u8] {

substrate/srml/support/procedural/src/storage/mod.rs

@@ -234,16 +234,6 @@ impl HasherKind {
 		}
 	}
 
-	fn into_hashable_fn(&self) -> TokenStream2 {
-		match self {
-			HasherKind::Blake2_256 => quote!( blake2_256 ),
-			HasherKind::Blake2_128 => quote!( blake2_128 ),
-			HasherKind::Twox256 => quote!( twox_256 ),
-			HasherKind::Twox128 => quote!( twox_128 ),
-			HasherKind::Twox64Concat => quote!( twox_64_concat),
-		}
-	}
-
 	fn into_metadata(&self) -> TokenStream2 {
 		match self {
 			HasherKind::Blake2_256 => quote!( StorageHasher::Blake2_256 ),

substrate/srml/support/procedural/src/storage/transformation.rs

@@ -596,7 +596,7 @@ fn decl_storage_items(
 				i.linked_map(hasher.into_storage_hasher_struct(), key_type)
 			},
 			DeclStorageTypeInfosKind::DoubleMap { key1_type, key2_type, key2_hasher, hasher } => {
-				i.double_map(hasher.into_hashable_fn(), key1_type, key2_type, key2_hasher)
+				i.double_map(hasher.into_storage_hasher_struct(), key1_type, key2_type, key2_hasher)
 			},
 		};
 		impls.extend(implementation)