lib.rs

		let maybe_state_snapshot: Option<SnapshotConfig> = var("SNAP").map(|s| s.into()).ok();
		let mut ext = Builder::<Block>::default()
			.mode(if let Some(state_snapshot) = maybe_state_snapshot {
				Mode::OfflineOrElseOnline(
					OfflineConfig { state_snapshot: state_snapshot.clone() },
					OnlineConfig {
						transport,
						state_snapshot: Some(state_snapshot),
						..Default::default()
					},
				)
			} else {
				Mode::Online(OnlineConfig { transport, ..Default::default() })
			})
			.build()
			.await
			.unwrap();
		ext.execute_with(|| Runtime::on_runtime_upgrade(UpgradeCheckSelect::PreAndPost));
	}
}

mod clean_state_migration {
	use super::Runtime;
	use frame_support::{pallet_prelude::*, storage_alias, traits::OnRuntimeUpgrade};
	use pallet_state_trie_migration::MigrationLimits;

	#[cfg(not(feature = "std"))]
	use sp_std::prelude::*;

	#[storage_alias]
	type AutoLimits = StorageValue<StateTrieMigration, Option<MigrationLimits>, ValueQuery>;

	// Actual type of value is `MigrationTask<T>`, putting a dummy
	// one to avoid the trait constraint on T.
	// Since we only use `kill` it is fine.
	#[storage_alias]
	type MigrationProcess = StorageValue<StateTrieMigration, u32, ValueQuery>;

	#[storage_alias]
	type SignedMigrationMaxLimits = StorageValue<StateTrieMigration, MigrationLimits, OptionQuery>;

	/// Initialize an automatic migration process.
	pub struct CleanMigrate;

	impl OnRuntimeUpgrade for CleanMigrate {
		#[cfg(feature = "try-runtime")]
		fn pre_upgrade() -> Result<Vec<u8>, &'static str> {
			Ok(Default::default())
		}

		fn on_runtime_upgrade() -> frame_support::weights::Weight {
			MigrationProcess::kill();
			AutoLimits::kill();
			SignedMigrationMaxLimits::kill();
			<Runtime as frame_system::Config>::DbWeight::get().writes(3)
		}

		#[cfg(feature = "try-runtime")]
		fn post_upgrade(_state: Vec<u8>) -> Result<(), &'static str> {
			frame_support::ensure!(
				!AutoLimits::exists() && !SignedMigrationMaxLimits::exists(),
				"State migration clean.",
			);
			Ok(())
		}
	}
}