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/support/test/tests/construct_runtime_ui/generics_in_invalid_module.stderr

@@ -1,4 +1,4 @@
-error: `Call` is not allowed to have generics. Only the following pallets are allowed to have generics: `Event`, `Error`, `Origin`, `Config`.
+error: `Call` is not allowed to have generics. Only the following pallets are allowed to have generics: `Event`, `Error`, `Origin`, `Config`, `Task`.
   --> tests/construct_runtime_ui/generics_in_invalid_module.rs:24:36
    |
 24 |         Balance: balances::<Instance1>::{Call<T>, Origin<T>},

substrate/frame/support/test/tests/construct_runtime_ui/invalid_module_details_keyword.stderr

@@ -1,4 +1,4 @@
-error: expected one of: `Pallet`, `Call`, `Storage`, `Event`, `Error`, `Config`, `Origin`, `Inherent`, `ValidateUnsigned`, `FreezeReason`, `HoldReason`, `LockId`, `SlashReason`
+error: expected one of: `Pallet`, `Call`, `Storage`, `Event`, `Error`, `Config`, `Origin`, `Inherent`, `ValidateUnsigned`, `FreezeReason`, `HoldReason`, `Task`, `LockId`, `SlashReason`
   --> tests/construct_runtime_ui/invalid_module_details_keyword.rs:23:20
    |
 23 |         system: System::{enum},

substrate/frame/support/test/tests/construct_runtime_ui/invalid_module_entry.stderr

@@ -1,4 +1,4 @@
-error: expected one of: `Pallet`, `Call`, `Storage`, `Event`, `Error`, `Config`, `Origin`, `Inherent`, `ValidateUnsigned`, `FreezeReason`, `HoldReason`, `LockId`, `SlashReason`
+error: expected one of: `Pallet`, `Call`, `Storage`, `Event`, `Error`, `Config`, `Origin`, `Inherent`, `ValidateUnsigned`, `FreezeReason`, `HoldReason`, `Task`, `LockId`, `SlashReason`
   --> tests/construct_runtime_ui/invalid_module_entry.rs:24:23
    |
 24 |         Balance: balances::{Unexpected},

substrate/frame/support/test/tests/construct_runtime_ui/number_of_pallets_exceeds_tuple_size.stderr

@@ -76,3 +76,11 @@ help: consider importing one of these items
    |
 18 + use frame_support::traits::PalletInfo;
    |
+
+error[E0412]: cannot find type `RuntimeTask` in this scope
+  --> tests/construct_runtime_ui/number_of_pallets_exceeds_tuple_size.rs:39:1
+   |
+39 | #[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: you might have meant to use the associated type: `Self::RuntimeTask`
+   |
+   = note: this error originates in the macro `frame_system::config_preludes::TestDefaultConfig` which comes from the expansion of the macro `frame_support::macro_magic::forward_tokens_verbatim` (in Nightly builds, run with -Z macro-backtrace for more info)

substrate/frame/support/test/tests/derive_impl_ui/inject_runtime_type_invalid.stderr

@@ -1,4 +1,4 @@
-error: `#[inject_runtime_type]` can only be attached to `RuntimeCall`, `RuntimeEvent`, `RuntimeOrigin` or `PalletInfo`
+error: `#[inject_runtime_type]` can only be attached to `RuntimeCall`, `RuntimeEvent`, `RuntimeTask`, `RuntimeOrigin` or `PalletInfo`
   --> tests/derive_impl_ui/inject_runtime_type_invalid.rs:32:5
    |
 32 |     type RuntimeInfo = ();

substrate/frame/support/test/tests/pallet_outer_enums_explicit.rs

@@ -90,6 +90,8 @@ fn module_error_outer_enum_expand_explicit() {
 			frame_system::Error::NonDefaultComposite => (),
 			frame_system::Error::NonZeroRefCount => (),
 			frame_system::Error::CallFiltered => (),
+			frame_system::Error::InvalidTask => (),
+			frame_system::Error::FailedTask => (),
 			frame_system::Error::__Ignore(_, _) => (),
 		},
 

substrate/frame/support/test/tests/pallet_outer_enums_implicit.rs

@@ -90,6 +90,8 @@ fn module_error_outer_enum_expand_implicit() {
 			frame_system::Error::NonDefaultComposite => (),
 			frame_system::Error::NonZeroRefCount => (),
 			frame_system::Error::CallFiltered => (),
+			frame_system::Error::InvalidTask => (),
+			frame_system::Error::FailedTask => (),
 			frame_system::Error::__Ignore(_, _) => (),
 		},
 

substrate/frame/support/test/tests/pallet_ui/composite_enum_unsupported_identifier.stderr

@@ -1,4 +1,4 @@
-error: expected one of: `FreezeReason`, `HoldReason`, `LockId`, `SlashReason`
+error: expected one of: `FreezeReason`, `HoldReason`, `LockId`, `SlashReason`, `Task`
   --> tests/pallet_ui/composite_enum_unsupported_identifier.rs:27:11
    |
 27 |     pub enum HoldReasons {}

substrate/frame/support/test/tests/pallet_ui/pass/task_valid.rs

@@ -0,0 +1,43 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::{ensure, pallet_prelude::DispatchResult};
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index(0)]
+		#[pallet::task_condition(|i, j| i == 0u32 && j == 2u64)]
+		#[pallet::task_list(vec![(0u32, 2u64), (2u32, 4u64)].iter())]
+		#[pallet::task_weight(0.into())]
+		fn foo(i: u32, j: u64) -> DispatchResult {
+			ensure!(i == 0, "i must be 0");
+			ensure!(j == 2, "j must be 2");
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_can_only_be_attached_to_impl.rs

@@ -0,0 +1,34 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+	#[pallet::tasks_experimental]
+    pub struct Task;
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_can_only_be_attached_to_impl.stderr

@@ -0,0 +1,5 @@
+error: expected `impl`
+  --> tests/pallet_ui/task_can_only_be_attached_to_impl.rs:30:5
+   |
+30 |     pub struct Task;
+   |     ^^^

substrate/frame/support/test/tests/pallet_ui/task_condition_invalid_arg.rs

@@ -0,0 +1,42 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index(0)]
+		#[pallet::task_condition(|flag: bool| flag)]
+		#[pallet::task_list(vec![1, 2].iter())]
+		#[pallet::task_weight(0.into())]
+		fn foo(_i: u32) -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_condition_invalid_arg.stderr

@@ -0,0 +1,22 @@
+error: unused import: `frame_system::pallet_prelude::OriginFor`
+  --> tests/pallet_ui/task_condition_invalid_arg.rs:21:6
+   |
+21 |     use frame_system::pallet_prelude::OriginFor;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D unused-imports` implied by `-D warnings`
+
+error[E0308]: mismatched types
+  --> tests/pallet_ui/task_condition_invalid_arg.rs:35:10
+   |
+32 |         #[pallet::task_condition(|flag: bool| flag)]
+   |                                  ----------------- arguments to this function are incorrect
+...
+35 |         fn foo(_i: u32) -> DispatchResult {
+   |                ^^ expected `bool`, found `u32`
+   |
+note: closure parameter defined here
+  --> tests/pallet_ui/task_condition_invalid_arg.rs:32:29
+   |
+32 |         #[pallet::task_condition(|flag: bool| flag)]
+   |                                   ^^^^^^^^^^

substrate/frame/support/test/tests/pallet_ui/task_invalid_condition.rs

@@ -0,0 +1,42 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index(0)]
+		#[pallet::task_condition(0)]
+		#[pallet::task_list(vec![1, 2].iter())]
+		#[pallet::task_weight(0.into())]
+		fn foo() -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_invalid_condition.stderr

@@ -0,0 +1,27 @@
+error: unused import: `frame_system::pallet_prelude::OriginFor`
+  --> tests/pallet_ui/task_invalid_condition.rs:21:6
+   |
+21 |     use frame_system::pallet_prelude::OriginFor;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D unused-imports` implied by `-D warnings`
+
+error[E0308]: mismatched types
+  --> tests/pallet_ui/task_invalid_condition.rs:18:1
+   |
+18 | #[frame_support::pallet(dev_mode)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | |
+   | expected integer, found `()`
+   | expected due to this
+   |
+   = note: this error originates in the attribute macro `frame_support::pallet` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0618]: expected function, found `{integer}`
+  --> tests/pallet_ui/task_invalid_condition.rs:32:28
+   |
+18 | #[frame_support::pallet(dev_mode)]
+   | ---------------------------------- call expression requires function
+...
+32 |         #[pallet::task_condition(0)]
+   |                                  ^

substrate/frame/support/test/tests/pallet_ui/task_invalid_index.rs

@@ -0,0 +1,39 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index("0")]
+		fn foo() -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_invalid_index.stderr

@@ -0,0 +1,5 @@
+error: expected integer literal
+  --> tests/pallet_ui/task_invalid_index.rs:31:24
+   |
+31 |         #[pallet::task_index("0")]
+   |                              ^^^

substrate/frame/support/test/tests/pallet_ui/task_invalid_list.rs

@@ -0,0 +1,42 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index(0)]
+		#[pallet::task_condition(|| true)]
+		#[pallet::task_list(0)]
+		#[pallet::task_weight(0.into())]
+		fn foo() -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_invalid_list.stderr

@@ -0,0 +1,19 @@
+error: unused import: `frame_system::pallet_prelude::OriginFor`
+  --> tests/pallet_ui/task_invalid_list.rs:21:6
+   |
+21 |     use frame_system::pallet_prelude::OriginFor;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D unused-imports` implied by `-D warnings`
+
+error[E0689]: can't call method `map` on ambiguous numeric type `{integer}`
+  --> tests/pallet_ui/task_invalid_list.rs:18:1
+   |
+18 | #[frame_support::pallet(dev_mode)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: this error originates in the attribute macro `frame_support::pallet` (in Nightly builds, run with -Z macro-backtrace for more info)
+help: you must specify a concrete type for this numeric value, like `i32`
+   |
+33 |         #[pallet::task_list(0_i32)]
+   |                             ~~~~~

substrate/frame/support/test/tests/pallet_ui/task_invalid_weight.rs

@@ -0,0 +1,42 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index(0)]
+		#[pallet::task_condition(|| true)]
+		#[pallet::task_list(vec![1, 2].iter())]
+		#[pallet::task_weight("0")]
+		fn foo() -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_invalid_weight.stderr

@@ -0,0 +1,27 @@
+error: unused import: `frame_system::pallet_prelude::OriginFor`
+  --> tests/pallet_ui/task_invalid_weight.rs:21:6
+   |
+21 |     use frame_system::pallet_prelude::OriginFor;
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D unused-imports` implied by `-D warnings`
+
+error[E0308]: mismatched types
+  --> tests/pallet_ui/task_invalid_weight.rs:18:1
+   |
+18 | #[frame_support::pallet(dev_mode)]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   | |
+   | expected integer, found `()`
+   | expected due to this
+   |
+   = note: this error originates in the attribute macro `frame_support::pallet` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0308]: mismatched types
+  --> tests/pallet_ui/task_invalid_weight.rs:34:25
+   |
+18 | #[frame_support::pallet(dev_mode)]
+   | ---------------------------------- expected `Weight` because of return type
+...
+34 |         #[pallet::task_weight("0")]
+   |                               ^^^ expected `Weight`, found `&str`

substrate/frame/support/test/tests/pallet_ui/task_missing_condition.rs

@@ -0,0 +1,39 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index(0)]
+		fn foo() -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_missing_condition.stderr

@@ -0,0 +1,5 @@
+error: missing `#[pallet::task_condition(..)]` attribute
+  --> tests/pallet_ui/task_missing_condition.rs:32:6
+   |
+32 |         fn foo() -> DispatchResult {
+   |            ^^^

substrate/frame/support/test/tests/pallet_ui/task_missing_index.rs

@@ -0,0 +1,38 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		fn foo() -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_missing_index.stderr

@@ -0,0 +1,5 @@
+error: missing `#[pallet::task_index(..)]` attribute
+  --> tests/pallet_ui/task_missing_index.rs:31:6
+   |
+31 |         fn foo() -> DispatchResult {
+   |            ^^^

substrate/frame/support/test/tests/pallet_ui/task_missing_list.rs

@@ -0,0 +1,40 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index(0)]
+		#[pallet::task_condition(|| true)]
+		fn foo() -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_missing_list.stderr

@@ -0,0 +1,5 @@
+error: missing `#[pallet::task_list(..)]` attribute
+  --> tests/pallet_ui/task_missing_list.rs:33:6
+   |
+33 |         fn foo() -> DispatchResult {
+   |            ^^^

substrate/frame/support/test/tests/pallet_ui/task_missing_weight.rs

@@ -0,0 +1,41 @@
+// 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.
+
+#[frame_support::pallet(dev_mode)]
+mod pallet {
+	use frame_support::pallet_prelude::DispatchResult;
+	use frame_system::pallet_prelude::OriginFor;
+
+	#[pallet::config]
+	pub trait Config: frame_system::Config {}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(core::marker::PhantomData<T>);
+
+    #[pallet::tasks_experimental]
+	impl<T: Config> Pallet<T> {
+		#[pallet::task_index(0)]
+		#[pallet::task_condition(|| true)]
+		#[pallet::task_list(vec![1, 2].iter())]
+		fn foo() -> DispatchResult {
+			Ok(())
+		}
+	}
+}
+
+fn main() {
+}

substrate/frame/support/test/tests/pallet_ui/task_missing_weight.stderr

@@ -0,0 +1,5 @@
+error: missing `#[pallet::task_weight(..)]` attribute
+  --> tests/pallet_ui/task_missing_weight.rs:34:6
+   |
+34 |         fn foo() -> DispatchResult {
+   |            ^^^