Tasks: general system for recognizing and executing service work (#1343)

`polkadot-sdk` version of original tasks PR located here:
https://github.com/paritytech/substrate/pull/14329

Fixes #206

## Status
- [x] Generic `Task` trait
- [x] `RuntimeTask` aggregated enum, compatible with
`construct_runtime!`
- [x] Casting between `Task` and `RuntimeTask` without needing `dyn` or
`Box`
- [x] Tasks Example pallet
- [x] Runtime tests for Tasks example pallet
- [x] Parsing for task-related macros
- [x] Retrofit parsing to make macros optional
- [x] Expansion for task-related macros
- [x] Adds support for args in tasks
- [x] Retrofit tasks example pallet to use macros instead of manual
syntax
- [x] Weights
- [x] Cleanup
- [x] UI tests
- [x] Docs

## Target Syntax
Adapted from
https://github.com/paritytech/polkadot-sdk/issues/206#issue-1865172283

```rust
// NOTE: this enum is optional and is auto-generated by the other macros if not present
#[pallet::task]
pub enum Task<T: Config> {
    AddNumberIntoTotal {
        i: u32,
    }
}

/// Some running total.
#[pallet::storage]
pub(super) type Total<T: Config<I>, I: 'static = ()> =
StorageValue<_, (u32, u32), ValueQuery>;

/// Numbers to be added into the total.
#[pallet::storage]
pub(super) type Numbers<T: Config<I>, I: 'static = ()> =
StorageMap<_, Twox64Concat, u32, u32, OptionQuery>;

#[pallet::tasks_experimental]
impl<T: Config<I>, I: 'static> Pallet<T, I> {
	/// Add a pair of numbers into the totals and remove them.
	#[pallet::task_list(Numbers::<T, I>::iter_keys())]
	#[pallet::task_condition(|i| Numbers::<T, I>::contains_key(i))]
	#[pallet::task_index(0)]
	pub fn add_number_into_total(i: u32) -> DispatchResult {
		let v = Numbers::<T, I>::take(i).ok_or(Error::<T, I>::NotFound)?;
		Total::<T, I>::mutate(|(total_keys, total_values)| {
			*total_keys += i;
			*total_values += v;
		});
		Ok(())
	}
}
```

---------

Co-authored-by: Nikhil Gupta <17176722+gupnik@users.noreply.github.com>
Co-authored-by: kianenigma <kian@parity.io>
Co-authored-by: Nikhil Gupta <>
Co-authored-by: Gavin Wood <gavin@parity.io>
Co-authored-by: Oliver Tale-Yazdi <oliver.tale-yazdi@parity.io>
Co-authored-by: gupnik <nikhilgupta.iitk@gmail.com>

substrate/frame/examples/tasks/src/tests.rs

@@ -0,0 +1,127 @@
+// 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.
+
+//! Tests for `pallet-example-tasks`.
+#![cfg(test)]
+
+use crate::{mock::*, Numbers, Total};
+use frame_support::{assert_noop, assert_ok, traits::Task};
+use sp_runtime::BuildStorage;
+
+// This function basically just builds a genesis storage key/value store according to
+// our desired mockup.
+pub fn new_test_ext() -> sp_io::TestExternalities {
+	let t = RuntimeGenesisConfig {
+		// We use default for brevity, but you can configure as desired if needed.
+		system: Default::default(),
+	}
+	.build_storage()
+	.unwrap();
+	t.into()
+}
+
+#[test]
+fn task_enumerate_works() {
+	new_test_ext().execute_with(|| {
+		Numbers::<Runtime>::insert(0, 1);
+		assert_eq!(crate::pallet::Task::<Runtime>::iter().collect::<Vec<_>>().len(), 1);
+	});
+}
+
+#[test]
+fn runtime_task_enumerate_works_via_frame_system_config() {
+	new_test_ext().execute_with(|| {
+		Numbers::<Runtime>::insert(0, 1);
+		Numbers::<Runtime>::insert(1, 4);
+		assert_eq!(
+			<Runtime as frame_system::Config>::RuntimeTask::iter().collect::<Vec<_>>().len(),
+			2
+		);
+	});
+}
+
+#[test]
+fn runtime_task_enumerate_works_via_pallet_config() {
+	new_test_ext().execute_with(|| {
+		Numbers::<Runtime>::insert(1, 4);
+		assert_eq!(
+			<Runtime as crate::pallet::Config>::RuntimeTask::iter()
+				.collect::<Vec<_>>()
+				.len(),
+			1
+		);
+	});
+}
+
+#[test]
+fn task_index_works_at_pallet_level() {
+	new_test_ext().execute_with(|| {
+		assert_eq!(crate::pallet::Task::<Runtime>::AddNumberIntoTotal { i: 2u32 }.task_index(), 0);
+	});
+}
+
+#[test]
+fn task_index_works_at_runtime_level() {
+	new_test_ext().execute_with(|| {
+		assert_eq!(
+			<Runtime as frame_system::Config>::RuntimeTask::TasksExample(crate::pallet::Task::<
+				Runtime,
+			>::AddNumberIntoTotal {
+				i: 1u32
+			})
+			.task_index(),
+			0
+		);
+	});
+}
+
+#[test]
+fn task_execution_works() {
+	new_test_ext().execute_with(|| {
+		System::set_block_number(1);
+		Numbers::<Runtime>::insert(0, 1);
+		Numbers::<Runtime>::insert(1, 4);
+
+		let task =
+			<Runtime as frame_system::Config>::RuntimeTask::TasksExample(crate::pallet::Task::<
+				Runtime,
+			>::AddNumberIntoTotal {
+				i: 1u32,
+			});
+		assert_ok!(System::do_task(RuntimeOrigin::signed(1), task.clone(),));
+		assert_eq!(Numbers::<Runtime>::get(0), Some(1));
+		assert_eq!(Numbers::<Runtime>::get(1), None);
+		assert_eq!(Total::<Runtime>::get(), (1, 4));
+		System::assert_last_event(frame_system::Event::<Runtime>::TaskCompleted { task }.into());
+	});
+}
+
+#[test]
+fn task_execution_fails_for_invalid_task() {
+	new_test_ext().execute_with(|| {
+		Numbers::<Runtime>::insert(1, 4);
+		assert_noop!(
+			System::do_task(
+				RuntimeOrigin::signed(1),
+				<Runtime as frame_system::Config>::RuntimeTask::TasksExample(
+					crate::pallet::Task::<Runtime>::AddNumberIntoTotal { i: 0u32 }
+				),
+			),
+			frame_system::Error::<Runtime>::InvalidTask
+		);
+	});
+}