Contracts: Ensure latest migration match pallet_version (#14676)

* Add version check

* fix format

* simplify

* restructure imports

* add version check

* Fix benchmarking

* Rename migrations -> BenchMigrations

* doc

* add more docs

* fix format string

* Update frame/contracts/build.rs

* fix

* add cargo:rerun-if-changed

---------

Co-authored-by: parity-processbot <>

substrate/frame/contracts/build.rs

@@ -0,0 +1,73 @@
+// 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.
+
+use std::io::Write;
+
+/// Get the latest migration version.
+///
+/// Find the highest version number from the available migration files.
+/// Each migration file should follow the naming convention `vXX.rs`, where `XX` is the version
+/// number.
+fn get_latest_version() -> u16 {
+	std::fs::read_dir("src/migration")
+		.expect("Folder `src/migration` not found.")
+		.filter_map(|entry| {
+			let file_name = entry.as_ref().ok()?.file_name();
+			let file_name = file_name.to_str()?;
+			if file_name.starts_with('v') && file_name.ends_with(".rs") {
+				let version = &file_name[1..&file_name.len() - 3];
+				let version = version.parse::<u16>().ok()?;
+
+				// Ensure that the version matches the one defined in the file.
+				let path = entry.unwrap().path();
+				let file_content = std::fs::read_to_string(&path).ok()?;
+				assert!(
+					file_content.contains(&format!("const VERSION: u16 = {}", version)),
+					"Invalid MigrationStep::VERSION in {:?}",
+					path
+				);
+
+				return Some(version)
+			}
+			None
+		})
+		.max()
+		.expect("Failed to find any files matching the 'src/migration/vxx.rs' pattern.")
+}
+
+/// Generates a module that exposes the latest migration version, and the benchmark migrations type.
+fn main() -> Result<(), Box<dyn std::error::Error>> {
+	let out_dir = std::env::var("OUT_DIR")?;
+	let path = std::path::Path::new(&out_dir).join("migration_codegen.rs");
+	let mut f = std::fs::File::create(&path)?;
+	let version = get_latest_version();
+	write!(
+		f,
+		"
+         pub mod codegen {{
+		  use crate::NoopMigration;
+		  /// The latest migration version, pulled from the latest migration file.
+		  pub const LATEST_MIGRATION_VERSION: u16 = {version};
+		  /// The Migration Steps used for benchmarking the migration framework.
+		  pub type BenchMigrations = (NoopMigration<{}>, NoopMigration<{version}>);
+		}}",
+		version - 1,
+	)?;
+
+	println!("cargo:rerun-if-changed=src/migration");
+	Ok(())
+}