Fuzzer for Pallet Bags List (#9851)

* Fuzzer for Pallet Bags List

* Some small updates

* Fuzzer for Pallet Bags List

This PR adds a fuzzer for the `SortedListProvider` API exposed by pallet-bags-list.

* Feature gate code NOT used by fuzz feature

* Create Enum for list actions

* fix some small mistakes

* try and make CI happy

* fmt

* Do not insert before updating

* clean up some misc. comments

* marginally improve Node::sanity_check

* Change ID_RANGE to 25_000

* comma

* try improve correct feature gating so no unused code

Co-authored-by: thiolliere <gui.thiolliere@gmail.com>

substrate/frame/bags-list/fuzzer/src/main.rs

@@ -0,0 +1,88 @@
+// This file is part of Substrate.
+
+// Copyright (C) 2021 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.
+
+//! # Running
+//! Running this fuzzer can be done with `cargo hfuzz run bags-list`. `honggfuzz` CLI options can
+//! be used by setting `HFUZZ_RUN_ARGS`, such as `-n 4` to use 4 threads.
+//!
+//! # Debugging a panic
+//! Once a panic is found, it can be debugged with
+//! `cargo hfuzz run-debug fixed_point hfuzz_workspace/bags_list/*.fuzz`.
+//!
+//! # More information
+//! More information about `honggfuzz` can be found
+//! [here](https://docs.rs/honggfuzz/).
+
+use frame_election_provider_support::{SortedListProvider, VoteWeight};
+use honggfuzz::fuzz;
+use pallet_bags_list::mock::{AccountId, BagsList, ExtBuilder};
+use std::convert::From;
+
+const ID_RANGE: AccountId = 25_000;
+
+/// Actions of a `SortedListProvider` that we fuzz.
+enum Action {
+	Insert,
+	Update,
+	Remove,
+}
+
+impl From<u32> for Action {
+	fn from(v: u32) -> Self {
+		let num_variants = Self::Remove as u32 + 1;
+		match v % num_variants {
+			_x if _x == Action::Insert as u32 => Action::Insert,
+			_x if _x == Action::Update as u32 => Action::Update,
+			_x if _x == Action::Remove as u32 => Action::Remove,
+			_ => unreachable!(),
+		}
+	}
+}
+
+fn main() {
+	ExtBuilder::default().build_and_execute(|| loop {
+		fuzz!(|data: (AccountId, VoteWeight, u32)| {
+			let (account_id_seed, vote_weight, action_seed) = data;
+
+			let id = account_id_seed % ID_RANGE;
+			let action = Action::from(action_seed);
+
+			match action {
+				Action::Insert => {
+					if BagsList::on_insert(id.clone(), vote_weight).is_err() {
+						// this was a duplicate id, which is ok. We can just update it.
+						BagsList::on_update(&id, vote_weight);
+					}
+					assert!(BagsList::contains(&id));
+				},
+				Action::Update => {
+					let already_contains = BagsList::contains(&id);
+					BagsList::on_update(&id, vote_weight);
+					if already_contains {
+						assert!(BagsList::contains(&id));
+					}
+				},
+				Action::Remove => {
+					BagsList::on_remove(&id);
+					assert!(!BagsList::contains(&id));
+				},
+			}
+
+			assert!(BagsList::sanity_check().is_ok());
+		})
+	});
+}