feat: compute pallet/storage prefix hash at compile time (#1539)

Since the hash rules of this part of the `pallet_prefix/storage_prefix`
are always fixed, we can put the runtime calculation into compile time.

---
polkadot address: 15ouFh2SHpGbHtDPsJ6cXQfes9Cx1gEFnJJsJVqPGzBSTudr

---------

Co-authored-by: Juan <juangirini@gmail.com>
Co-authored-by: command-bot <>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>

substrate/frame/support/procedural/src/construct_runtime/mod.rs

@@ -211,6 +211,7 @@
 mod expand;
 mod parse;
 
+use crate::pallet::parse::helper::two128_str;
 use cfg_expr::Predicate;
 use frame_support_procedural_tools::{
 	generate_crate_access, generate_crate_access_2018, generate_hidden_includes,
@@ -403,17 +404,19 @@ fn construct_runtime_final_expansion(
 	let integrity_test = decl_integrity_test(&scrate);
 	let static_assertions = decl_static_assertions(&name, &pallets, &scrate);
 
-	let warning =
-		where_section.map_or(None, |where_section| {
-			Some(proc_macro_warning::Warning::new_deprecated("WhereSection")
-			.old("use a `where` clause in `construct_runtime`")
-			.new("use `frame_system::Config` to set the `Block` type and delete this clause. 
-				It is planned to be removed in December 2023")
-			.help_links(&["https://github.com/paritytech/substrate/pull/14437"])
-			.span(where_section.span)
-			.build(),
+	let warning = where_section.map_or(None, |where_section| {
+		Some(
+			proc_macro_warning::Warning::new_deprecated("WhereSection")
+				.old("use a `where` clause in `construct_runtime`")
+				.new(
+					"use `frame_system::Config` to set the `Block` type and delete this clause.
+				It is planned to be removed in December 2023",
+				)
+				.help_links(&["https://github.com/paritytech/substrate/pull/14437"])
+				.span(where_section.span)
+				.build(),
 		)
-		});
+	});
 
 	let res = quote!(
 		#warning
@@ -659,7 +662,6 @@ fn decl_all_pallets<'a>(
 		#( #all_pallets_reversed_with_system_first )*
 	)
 }
-
 fn decl_pallet_runtime_setup(
 	runtime: &Ident,
 	pallet_declarations: &[Pallet],
@@ -667,6 +669,7 @@ fn decl_pallet_runtime_setup(
 ) -> TokenStream2 {
 	let names = pallet_declarations.iter().map(|d| &d.name).collect::<Vec<_>>();
 	let name_strings = pallet_declarations.iter().map(|d| d.name.to_string());
+	let name_hashes = pallet_declarations.iter().map(|d| two128_str(&d.name.to_string()));
 	let module_names = pallet_declarations.iter().map(|d| d.path.module_name());
 	let indices = pallet_declarations.iter().map(|pallet| pallet.index as usize);
 	let pallet_structs = pallet_declarations
@@ -699,6 +702,7 @@ fn decl_pallet_runtime_setup(
 		pub struct PalletInfo;
 
 		impl #scrate::traits::PalletInfo for PalletInfo {
+
 			fn index<P: 'static>() -> Option<usize> {
 				let type_id = #scrate::__private::sp_std::any::TypeId::of::<P>();
 				#(
@@ -723,6 +727,18 @@ fn decl_pallet_runtime_setup(
 				None
 			}
 
+			fn name_hash<P: 'static>() -> Option<[u8; 16]> {
+				let type_id = #scrate::__private::sp_std::any::TypeId::of::<P>();
+				#(
+					#pallet_attrs
+					if type_id == #scrate::__private::sp_std::any::TypeId::of::<#names>() {
+						return Some(#name_hashes)
+					}
+				)*
+
+				None
+			}
+
 			fn module_name<P: 'static>() -> Option<&'static str> {
 				let type_id = #scrate::__private::sp_std::any::TypeId::of::<P>();
 				#(

substrate/frame/support/procedural/src/pallet/expand/pallet_struct.rs

@@ -246,6 +246,14 @@ pub fn expand_pallet_struct(def: &mut Def) -> proc_macro2::TokenStream {
 						implemented by the runtime")
 			}
 
+			fn name_hash() -> [u8; 16] {
+				<
+					<T as #frame_system::Config>::PalletInfo as #frame_support::traits::PalletInfo
+				>::name_hash::<Self>()
+					.expect("Pallet is part of the runtime because pallet `Config` trait is \
+						implemented by the runtime")
+			}
+
 			fn module_name() -> &'static str {
 				<
 					<T as #frame_system::Config>::PalletInfo as #frame_support::traits::PalletInfo

substrate/frame/support/procedural/src/pallet/expand/storage.rs

@@ -18,7 +18,10 @@
 use crate::{
 	counter_prefix,
 	pallet::{
-		parse::storage::{Metadata, QueryKind, StorageDef, StorageGenerics},
+		parse::{
+			helper::two128_str,
+			storage::{Metadata, QueryKind, StorageDef, StorageGenerics},
+		},
 		Def,
 	},
 };
@@ -638,6 +641,7 @@ pub fn expand_storages(def: &mut Def) -> proc_macro2::TokenStream {
 			Metadata::CountedMap { .. } => {
 				let counter_prefix_struct_ident = counter_prefix_ident(&storage_def.ident);
 				let counter_prefix_struct_const = counter_prefix(&prefix_struct_const);
+				let storage_prefix_hash = two128_str(&counter_prefix_struct_const);
 				quote::quote_spanned!(storage_def.attr_span =>
 					#(#cfg_attrs)*
 					#[doc(hidden)]
@@ -656,7 +660,19 @@ pub fn expand_storages(def: &mut Def) -> proc_macro2::TokenStream {
 							>::name::<Pallet<#type_use_gen>>()
 								.expect("No name found for the pallet in the runtime! This usually means that the pallet wasn't added to `construct_runtime!`.")
 						}
+
+						fn pallet_prefix_hash() -> [u8; 16] {
+							<
+								<T as #frame_system::Config>::PalletInfo
+								as #frame_support::traits::PalletInfo
+							>::name_hash::<Pallet<#type_use_gen>>()
+								.expect("No name_hash found for the pallet in the runtime! This usually means that the pallet wasn't added to `construct_runtime!`.")
+						}
+
 						const STORAGE_PREFIX: &'static str = #counter_prefix_struct_const;
+						fn storage_prefix_hash() -> [u8; 16] {
+							#storage_prefix_hash
+						}
 					}
 					#(#cfg_attrs)*
 					impl<#type_impl_gen> #frame_support::storage::types::CountedStorageMapInstance
@@ -670,6 +686,7 @@ pub fn expand_storages(def: &mut Def) -> proc_macro2::TokenStream {
 			Metadata::CountedNMap { .. } => {
 				let counter_prefix_struct_ident = counter_prefix_ident(&storage_def.ident);
 				let counter_prefix_struct_const = counter_prefix(&prefix_struct_const);
+				let storage_prefix_hash = two128_str(&counter_prefix_struct_const);
 				quote::quote_spanned!(storage_def.attr_span =>
 					#(#cfg_attrs)*
 					#[doc(hidden)]
@@ -688,7 +705,17 @@ pub fn expand_storages(def: &mut Def) -> proc_macro2::TokenStream {
 							>::name::<Pallet<#type_use_gen>>()
 								.expect("No name found for the pallet in the runtime! This usually means that the pallet wasn't added to `construct_runtime!`.")
 						}
+						fn pallet_prefix_hash() -> [u8; 16] {
+							<
+								<T as #frame_system::Config>::PalletInfo
+								as #frame_support::traits::PalletInfo
+							>::name_hash::<Pallet<#type_use_gen>>()
+								.expect("No name_hash found for the pallet in the runtime! This usually means that the pallet wasn't added to `construct_runtime!`.")
+						}
 						const STORAGE_PREFIX: &'static str = #counter_prefix_struct_const;
+						fn storage_prefix_hash() -> [u8; 16] {
+							#storage_prefix_hash
+						}
 					}
 					#(#cfg_attrs)*
 					impl<#type_impl_gen> #frame_support::storage::types::CountedStorageNMapInstance
@@ -702,6 +729,7 @@ pub fn expand_storages(def: &mut Def) -> proc_macro2::TokenStream {
 			_ => proc_macro2::TokenStream::default(),
 		};
 
+		let storage_prefix_hash = two128_str(&prefix_struct_const);
 		quote::quote_spanned!(storage_def.attr_span =>
 			#maybe_counter
 
@@ -722,7 +750,19 @@ pub fn expand_storages(def: &mut Def) -> proc_macro2::TokenStream {
 					>::name::<Pallet<#type_use_gen>>()
 						.expect("No name found for the pallet in the runtime! This usually means that the pallet wasn't added to `construct_runtime!`.")
 				}
+
+				fn pallet_prefix_hash() -> [u8; 16] {
+					<
+						<T as #frame_system::Config>::PalletInfo
+						as #frame_support::traits::PalletInfo
+					>::name_hash::<Pallet<#type_use_gen>>()
+						.expect("No name_hash found for the pallet in the runtime! This usually means that the pallet wasn't added to `construct_runtime!`.")
+				}
+
 				const STORAGE_PREFIX: &'static str = #prefix_struct_const;
+				fn storage_prefix_hash() -> [u8; 16] {
+					#storage_prefix_hash
+				}
 			}
 		)
 	});

substrate/frame/support/procedural/src/pallet/mod.rs

@@ -26,7 +26,7 @@
 //!   to user defined types. And also crate new types and implement block.
 
 mod expand;
-mod parse;
+pub(crate) mod parse;
 
 pub use parse::{composite::keyword::CompositeKeyword, Def};
 use syn::spanned::Spanned;

substrate/frame/support/procedural/src/pallet/parse/helper.rs

@@ -15,7 +15,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-use quote::ToTokens;
+use proc_macro2::TokenStream;
+use quote::{quote, ToTokens};
 use syn::spanned::Spanned;
 
 /// List of additional token to be used for parsing.
@@ -610,3 +611,16 @@ pub fn check_pallet_call_return_type(type_: &syn::Type) -> syn::Result<()> {
 
 	syn::parse2::<Checker>(type_.to_token_stream()).map(|_| ())
 }
+
+pub(crate) fn two128_str(s: &str) -> TokenStream {
+	bytes_to_array(sp_core_hashing::twox_128(s.as_bytes()).into_iter())
+}
+
+pub(crate) fn bytes_to_array(bytes: impl IntoIterator<Item = u8>) -> TokenStream {
+	let bytes = bytes.into_iter();
+
+	quote!(
+		[ #( #bytes ),* ]
+	)
+	.into()
+}

substrate/frame/support/procedural/src/storage_alias.rs

@@ -17,7 +17,7 @@
 
 //! Implementation of the `storage_alias` attribute macro.
 
-use crate::counter_prefix;
+use crate::{counter_prefix, pallet::parse::helper};
 use frame_support_procedural_tools::generate_crate_access_2018;
 use proc_macro2::{Span, TokenStream};
 use quote::{quote, ToTokens};
@@ -619,6 +619,7 @@ fn generate_storage_instance(
 	let counter_code = is_counted_map.then(|| {
 		let counter_name = Ident::new(&counter_prefix(&name_str), Span::call_site());
 		let counter_storage_name_str = counter_prefix(&storage_name_str);
+		let storage_prefix_hash = helper::two128_str(&counter_storage_name_str);
 
 		quote! {
 			#visibility struct #counter_name< #impl_generics >(
@@ -633,6 +634,9 @@ fn generate_storage_instance(
 				}
 
 				const STORAGE_PREFIX: &'static str = #counter_storage_name_str;
+				fn storage_prefix_hash() -> [u8; 16] {
+					#storage_prefix_hash
+				}
 			}
 
 			impl<#impl_generics> #crate_::storage::types::CountedStorageMapInstance
@@ -643,6 +647,8 @@ fn generate_storage_instance(
 		}
 	});
 
+	let storage_prefix_hash = helper::two128_str(&storage_name_str);
+
 	// Implement `StorageInstance` trait.
 	let code = quote! {
 		#[allow(non_camel_case_types)]
@@ -658,6 +664,9 @@ fn generate_storage_instance(
 			}
 
 			const STORAGE_PREFIX: &'static str = #storage_name_str;
+			fn storage_prefix_hash() -> [u8; 16] {
+				#storage_prefix_hash
+			}
 		}
 
 		#counter_code