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/src/traits/metadata.rs

@@ -31,6 +31,8 @@ pub trait PalletInfo {
 	fn index<P: 'static>() -> Option<usize>;
 	/// Convert the given pallet `P` into its name as configured in the runtime.
 	fn name<P: 'static>() -> Option<&'static str>;
+	/// The two128 hash of name.
+	fn name_hash<P: 'static>() -> Option<[u8; 16]>;
 	/// Convert the given pallet `P` into its Rust module name as used in `construct_runtime!`.
 	fn module_name<P: 'static>() -> Option<&'static str>;
 	/// Convert the given pallet `P` into its containing crate version.
@@ -59,6 +61,8 @@ pub trait PalletInfoAccess {
 	fn index() -> usize;
 	/// Name of the pallet as configured in the runtime.
 	fn name() -> &'static str;
+	/// Two128 hash of name.
+	fn name_hash() -> [u8; 16];
 	/// Name of the Rust module containing the pallet.
 	fn module_name() -> &'static str;
 	/// Version of the crate containing the pallet.
@@ -281,6 +285,7 @@ pub trait GetStorageVersion {
 #[cfg(test)]
 mod tests {
 	use super::*;
+	use sp_core::twox_128;
 
 	struct Pallet1;
 	impl PalletInfoAccess for Pallet1 {
@@ -290,6 +295,9 @@ mod tests {
 		fn name() -> &'static str {
 			"Pallet1"
 		}
+		fn name_hash() -> [u8; 16] {
+			twox_128(Self::name().as_bytes())
+		}
 		fn module_name() -> &'static str {
 			"pallet1"
 		}
@@ -305,6 +313,11 @@ mod tests {
 		fn name() -> &'static str {
 			"Pallet2"
 		}
+
+		fn name_hash() -> [u8; 16] {
+			twox_128(Self::name().as_bytes())
+		}
+
 		fn module_name() -> &'static str {
 			"pallet2"
 		}

substrate/frame/support/src/traits/storage.rs

@@ -61,8 +61,35 @@ pub trait StorageInstance {
 	/// Prefix of a pallet to isolate it from other pallets.
 	fn pallet_prefix() -> &'static str;
 
+	/// Return the prefix hash of pallet instance.
+	///
+	/// NOTE: This hash must be `twox_128(pallet_prefix())`.
+	/// Should not impl this function by hand. Only use the default or macro generated impls.
+	fn pallet_prefix_hash() -> [u8; 16] {
+		sp_io::hashing::twox_128(Self::pallet_prefix().as_bytes())
+	}
+
 	/// Prefix given to a storage to isolate from other storages in the pallet.
 	const STORAGE_PREFIX: &'static str;
+
+	/// Return the prefix hash of storage instance.
+	///
+	/// NOTE: This hash must be `twox_128(STORAGE_PREFIX)`.
+	fn storage_prefix_hash() -> [u8; 16] {
+		sp_io::hashing::twox_128(Self::STORAGE_PREFIX.as_bytes())
+	}
+
+	/// Return the prefix hash of instance.
+	///
+	/// NOTE: This hash must be `twox_128(pallet_prefix())++twox_128(STORAGE_PREFIX)`.
+	/// Should not impl this function by hand. Only use the default or macro generated impls.
+	fn prefix_hash() -> [u8; 32] {
+		let mut final_key = [0u8; 32];
+		final_key[..16].copy_from_slice(&Self::pallet_prefix_hash());
+		final_key[16..].copy_from_slice(&Self::storage_prefix_hash());
+
+		final_key
+	}
 }
 
 /// Metadata about storage from the runtime.