[doc] Example MBM pallet (paritytech#2119)

## Basic example showcasing a migration using the MBM framework

This PR has been built on top of
paritytech#1781 and adds two new
example crates to the `examples` pallet

### Changes Made:

Added the `pallet-example-mbm` crate: This crate provides a minimal
example of a pallet that uses MBM. It showcases a storage migration
where values are migrated from a `u32` to a `u64`.

---------

Signed-off-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: Liam Aharon <liam.aharon@hotmail.com>

Cargo.toml

@@ -331,6 +331,7 @@ members = [
 	"substrate/frame/examples/dev-mode",
 	"substrate/frame/examples/frame-crate",
 	"substrate/frame/examples/kitchensink",
+	"substrate/frame/examples/multi-block-migrations",
 	"substrate/frame/examples/offchain-worker",
 	"substrate/frame/examples/single-block-migrations",
 	"substrate/frame/examples/split",

prdoc/pr_2119.prdoc

@@ -0,0 +1,16 @@
+title: "Add example pallet for Multi-Block-Migrations"
+
+doc:
+  - audience: Runtime Dev
+    description: |
+      - Add an example pallet to demonstrate Multi-Block-Migrations.
+      - Add a `MigrationId` to frame-support for more convenient identification or migrations.
+      - Add default config prelude for testing in pallet-migrations.
+
+crates:
+  - name: frame-support
+    bump: minor
+  - name: pallet-migrations
+    bump: minor
+  - name: kitchensink-runtime
+    bump: patch

substrate/bin/node/runtime/Cargo.toml

@@ -89,6 +89,7 @@ pallet-elections-phragmen = { path = "../../../frame/elections-phragmen", defaul
 pallet-example-tasks = { path = "../../../frame/examples/tasks", default-features = false }
 pallet-fast-unstake = { path = "../../../frame/fast-unstake", default-features = false }
 pallet-migrations = { path = "../../../frame/migrations", default-features = false }
+pallet-example-mbm = { path = "../../../frame/examples/multi-block-migrations", default-features = false }
 pallet-nis = { path = "../../../frame/nis", default-features = false }
 pallet-grandpa = { path = "../../../frame/grandpa", default-features = false }
 pallet-im-online = { path = "../../../frame/im-online", default-features = false }
@@ -188,6 +189,7 @@ std = [
 	"pallet-election-provider-multi-phase/std",
 	"pallet-election-provider-support-benchmarking?/std",
 	"pallet-elections-phragmen/std",
+	"pallet-example-mbm/std",
 	"pallet-example-tasks/std",
 	"pallet-fast-unstake/std",
 	"pallet-glutton/std",
@@ -294,6 +296,7 @@ runtime-benchmarks = [
 	"pallet-election-provider-multi-phase/runtime-benchmarks",
 	"pallet-election-provider-support-benchmarking/runtime-benchmarks",
 	"pallet-elections-phragmen/runtime-benchmarks",
+	"pallet-example-mbm/runtime-benchmarks",
 	"pallet-example-tasks/runtime-benchmarks",
 	"pallet-fast-unstake/runtime-benchmarks",
 	"pallet-glutton/runtime-benchmarks",
@@ -373,6 +376,7 @@ try-runtime = [
 	"pallet-democracy/try-runtime",
 	"pallet-election-provider-multi-phase/try-runtime",
 	"pallet-elections-phragmen/try-runtime",
+	"pallet-example-mbm/try-runtime",
 	"pallet-example-tasks/try-runtime",
 	"pallet-fast-unstake/try-runtime",
 	"pallet-glutton/try-runtime",

substrate/bin/node/runtime/src/lib.rs

@@ -320,6 +320,8 @@ impl pallet_example_tasks::Config for Runtime {
 	type WeightInfo = pallet_example_tasks::weights::SubstrateWeight<Runtime>;
 }
 
+impl pallet_example_mbm::Config for Runtime {}
+
 impl pallet_utility::Config for Runtime {
 	type RuntimeEvent = RuntimeEvent;
 	type RuntimeCall = RuntimeCall;
@@ -2439,6 +2441,9 @@ mod runtime {
 
 	#[runtime::pallet_index(77)]
 	pub type SkipFeelessPayment = pallet_skip_feeless_payment;
+
+	#[runtime::pallet_index(78)]
+	pub type PalletExampleMbms = pallet_example_mbm;
 }
 
 /// The address format for describing accounts.
@@ -2597,6 +2602,7 @@ mod benches {
 		[pallet_whitelist, Whitelist]
 		[pallet_tx_pause, TxPause]
 		[pallet_safe_mode, SafeMode]
+		[pallet_example_mbm, PalletExampleMbms]
 	);
 }
 

substrate/frame/examples/multi-block-migrations/Cargo.toml

@@ -0,0 +1,47 @@
+[package]
+name = "pallet-example-mbm"
+version = "0.1.0"
+authors.workspace = true
+edition.workspace = true
+license = "Apache-2.0"
+homepage = "https://substrate.io"
+repository.workspace = true
+description = "Example FRAME pallet for multi-block migrations"
+publish = false
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[dependencies]
+codec = { package = "parity-scale-codec", version = "3.6.5", default-features = false }
+pallet-migrations = { path = "../../migrations", default-features = false }
+frame-support = { path = "../../support", default-features = false }
+frame-system = { path = "../../system", default-features = false }
+frame-benchmarking = { path = "../../benchmarking", default-features = false, optional = true }
+log = { version = "0.4.20", default-features = false }
+scale-info = { version = "2.10.0", default-features = false }
+sp-io = { path = "../../../primitives/io", default-features = false }
+
+[features]
+default = ["std"]
+std = [
+	"codec/std",
+	"frame-benchmarking?/std",
+	"frame-support/std",
+	"frame-system/std",
+	"log/std",
+	"pallet-migrations/std",
+	"scale-info/std",
+	"sp-io/std",
+]
+runtime-benchmarks = [
+	"frame-benchmarking/runtime-benchmarks",
+	"frame-support/runtime-benchmarks",
+	"frame-system/runtime-benchmarks",
+	"pallet-migrations/runtime-benchmarks",
+]
+try-runtime = [
+	"frame-support/try-runtime",
+	"frame-system/try-runtime",
+	"pallet-migrations/try-runtime",
+]

substrate/frame/examples/multi-block-migrations/src/lib.rs

@@ -0,0 +1,87 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+//! # Multi-Block Migrations Example Pallet
+//!
+//! This pallet serves as a minimal example of a pallet that uses the [Multi-Block Migrations
+//! Framework](frame_support::migrations). You can observe how to configure it in a runtime in the
+//! `kitchensink-runtime` crate.
+//!
+//! ## Introduction and Purpose
+//!
+//! The primary purpose of this pallet is to demonstrate the concept of Multi-Block Migrations in
+//! Substrate. It showcases the migration of values from in the
+//! [`MyMap`](`pallet::MyMap`) storage map a `u32` to a `u64` data type using the
+//! [`SteppedMigration`](`frame_support::migrations::SteppedMigration`) implementation from the
+//! [`migrations::v1`] module.
+//!
+//! The [`MyMap`](`pallet::MyMap`) storage item is defined in this `pallet`, and is
+//! aliased to [`v0::MyMap`](`migrations::v1::v0::MyMap`) in the [`migrations::v1`]
+//! module.
+//!
+//! ## How to Read the Documentation
+//!
+//! To access and navigate this documentation in your browser, use the following command:
+//!
+//! - `cargo doc --package pallet-example-mbm --open`
+//!
+//! This documentation is organized to help you understand the pallet's components, features, and
+//! migration process.
+//!
+//! ## Example Usage
+//!
+//! To use this pallet and understand multi-block migrations, you can refer to the
+//! [`migrations::v1`] module, which contains a step-by-step migration example.
+//!
+//! ## Pallet Structure
+//!
+//! The pallet is structured as follows:
+//!
+//! - [`migrations`]: Contains migration-related modules and migration logic.
+//!   - [`v1`](`migrations::v1`): Demonstrates the migration process for changing the data type in
+//!     the storage map.
+//! - [`pallet`]: Defines the pallet configuration and storage items.
+//!
+//! ## Migration Safety
+//!
+//! When working with migrations, it's crucial to ensure the safety of your migrations. The
+//! preferred tool to test migrations is
+//! [`try-runtime-cli`](https://github.com/paritytech/try-runtime-cli). Support will be added to
+//! dry-run MBMs once they are stable
+//! (tracked: <https://github.com/paritytech/try-runtime-cli/issues/17>).
+
+pub mod migrations;
+mod mock;
+
+pub use pallet::*;
+
+#[frame_support::pallet]
+pub mod pallet {
+	use frame_support::{pallet_prelude::StorageMap, Blake2_128Concat};
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(_);
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	/// Define a storage item to illustrate multi-block migrations.
+	#[pallet::storage]
+	pub type MyMap<T: Config> = StorageMap<_, Blake2_128Concat, u32, u64>;
+}

substrate/frame/examples/multi-block-migrations/src/migrations/mod.rs

@@ -0,0 +1,29 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+/// # Multi-Block Migrations Module
+///
+/// This module showcases a simple use of the multi-block migrations framework.
+pub mod v1;
+
+/// A unique identifier across all pallets.
+///
+/// This constant represents a unique identifier for the migrations of this pallet.
+/// It helps differentiate migrations for this pallet from those of others. Note that we don't
+/// directly pull the crate name from the environment, since that would change if the crate were
+/// ever to be renamed and could cause historic migrations to run again.
+pub const PALLET_MIGRATIONS_ID: &[u8; 18] = b"pallet-example-mbm";

substrate/frame/examples/multi-block-migrations/src/migrations/v1/benchmarks.rs

@@ -0,0 +1,54 @@
+// This file is part of Substrate.
+
+// Copyright (C) Parity Technologies (UK) Ltd.
+// SPDX-License-Identifier: Apache-2.0
+
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 	http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Benchmark the multi-block-migration.
+
+#![cfg(feature = "runtime-benchmarks")]
+
+use crate::{
+	migrations::{
+		v1,
+		v1::{weights, weights::WeightInfo},
+	},
+	Config, Pallet,
+};
+use frame_benchmarking::v2::*;
+use frame_support::{migrations::SteppedMigration, weights::WeightMeter};
+
+#[benchmarks]
+mod benches {
+	use super::*;
+
+	/// Benchmark a single step of the `v1::LazyMigrationV1` migration.
+	#[benchmark]
+	fn step() {
+		v1::v0::MyMap::<T>::insert(0, 0);
+		let mut meter = WeightMeter::new();
+
+		#[block]
+		{
+			v1::LazyMigrationV1::<T, weights::SubstrateWeight<T>>::step(None, &mut meter).unwrap();
+		}
+
+		// Check that the new storage is decodable:
+		assert_eq!(crate::MyMap::<T>::get(0), Some(0));
+		// uses twice the weight once for migration and then for checking if there is another key.
+		assert_eq!(meter.consumed(), weights::SubstrateWeight::<T>::step() * 2);
+	}
+
+	impl_benchmark_test_suite!(Pallet, crate::mock::new_test_ext(), crate::mock::Runtime);
+}