[FRAME Core] Default Pallet Config Trait / derive_impl

Cargo.toml

@@ -109,6 +109,7 @@ members = [
 	"frame/examples/basic",
 	"frame/examples/offchain-worker",
 	"frame/examples/dev-mode",
+	"frame/examples/default-config",
 	"frame/executive",
 	"frame/nis",
 	"frame/grandpa",

frame/examples/default-config/Cargo.toml

@@ -0,0 +1,38 @@
+[package]
+name = "pallet-default-config-example"
+version = "4.0.0-dev"
+authors = ["Parity Technologies <admin@parity.io>"]
+edition = "2021"
+license = "MIT-0"
+homepage = "https://substrate.io"
+repository = "https://github.com/paritytech/substrate/"
+description = "FRAME example pallet demonstrating derive_impl / default_config in action"
+readme = "README.md"
+
+[package.metadata.docs.rs]
+targets = ["x86_64-unknown-linux-gnu"]
+
+[dependencies]
+codec = { package = "parity-scale-codec", version = "3.2.2", default-features = false }
+log = { version = "0.4.17", default-features = false }
+scale-info = { version = "2.5.0", default-features = false, features = ["derive"] }
+frame-support = { default-features = false, path = "../../support" }
+frame-system = { default-features = false, path = "../../system" }
+
+sp-io = { default-features = false, path = "../../../primitives/io" }
+sp-runtime = { default-features = false, path = "../../../primitives/runtime" }
+sp-std = { default-features = false, path = "../../../primitives/std" }
+
+[features]
+default = ["std"]
+std = [
+	"codec/std",
+	"frame-support/std",
+	"frame-system/std",
+	"log/std",
+	"scale-info/std",
+	"sp-io/std",
+	"sp-runtime/std",
+	"sp-std/std",
+]
+try-runtime = ["frame-support/try-runtime"]

frame/examples/default-config/README.md

@@ -0,0 +1,8 @@
+# Default Config Example Pallet
+
+An example pallet demonstrating the ability to derive default testing configs via
+`#[derive_impl]` and `#[pallet::config(with_default)]`.
+
+Run `cargo doc --package pallet-default-config-example --open` to view this pallet's documentation.
+
+License: MIT-0

frame/examples/default-config/src/lib.rs

@@ -0,0 +1,210 @@
+// 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.
+
+//! # Default Config Pallet Example
+//!
+//! A simple example of a FRAME pallet that utilizes [`frame_support::derive_impl`] to demonstrate
+//! the simpler way to implement `Config` trait of pallets. This example only showcases this in a
+//! `mock.rs` environment, but the same applies to a real runtime as well.
+//!
+//! See the source code of [`tests`] for a real examples.
+//!
+//! Study the following types:
+//!
+//! - [`pallet::DefaultConfig`], and how it differs from [`pallet::Config`].
+//! - [`pallet::config_preludes::TestDefaultConfig`] and how it implements
+//!   [`pallet::DefaultConfig`].
+//! - Notice how [`pallet::DefaultConfig`] is independent of [`frame_system::Config`].
+
+#![cfg_attr(not(feature = "std"), no_std)]
+
+#[frame_support::pallet]
+pub mod pallet {
+	use frame_support::pallet_prelude::*;
+
+	/// This pallet is annotated to have a default config. This will auto-generate
+	/// [`DefaultConfig`].
+	///
+	/// It will be an identical, but won't have anything that is `#[pallet::no_default]`.
+	#[pallet::config(with_default)]
+	pub trait Config: frame_system::Config {
+		/// The overarching event type. This is coming from the runtime, and cannot have a default.
+		/// In general, `Runtime*`-oriented types cannot have a sensible default.
+		#[pallet::no_default] // optional. `RuntimeEvent` is automatically excluded as well.
+		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;
+
+		/// An input parameter to this pallet. This value can have a default, because it is not
+		/// reliant on `frame_system::Config` or the overarching runtime in any way.
+		type WithDefaultValue: Get<u32>;
+
+		/// Same as [`Config::WithDefaultValue`], but we don't intend to define a default for this
+		/// in our tests below.
+		type OverwrittenDefaultValue: Get<u32>;
+
+		/// An input parameter that relies on `<Self as frame_system::Config>::AccountId`. As of
+		/// now, such types cannot have defaults and need to be annotated as such, iff
+		/// `#[pallet::config(with_default)]` is enabled:
+		#[pallet::no_default]
+		type CannotHaveDefault: Get<Self::AccountId>;
+
+		/// Something that is a normal type, with default.
+		type WithDefaultType;
+
+		/// Same as [`Config::WithDefaultType`], but we don't intend to define a default for this
+		/// in our tests below.
+		type OverwrittenDefaultType;
+	}
+
+	/// Container for different types that implement [`DefaultConfig`]` of this pallet.
+	pub mod config_preludes {
+		// This will help use not need to disambiguate anything when using `derive_impl`.
+		use super::*;
+
+		/// A type providing default configurations for this pallet in testing environment.
+		pub struct TestDefaultConfig;
+		#[frame_support::register_default_impl(TestDefaultConfig)]
+		impl DefaultConfig for TestDefaultConfig {
+			type WithDefaultValue = frame_support::traits::ConstU32<42>;
+			type OverwrittenDefaultValue = frame_support::traits::ConstU32<42>;
+
+			type WithDefaultType = u32;
+			type OverwrittenDefaultType = u32;
+		}
+
+		/// A type providing default configurations for this pallet in a parachain environment.
+		pub struct ParachainDefaultConfig;
+		#[frame_support::register_default_impl(ParachainDefaultConfig)]
+		impl DefaultConfig for ParachainDefaultConfig {
+			type WithDefaultValue = frame_support::traits::ConstU32<66>;
+			type OverwrittenDefaultValue = frame_support::traits::ConstU32<66>;
+			type WithDefaultType = u32;
+			type OverwrittenDefaultType = u32;
+		}
+	}
+
+	#[pallet::pallet]
+	pub struct Pallet<T>(_);
+
+	#[pallet::event]
+	pub enum Event<T: Config> {}
+}
+
+#[cfg(any(test, doc))]
+pub mod tests {
+	use super::*;
+
+	use frame_support::macro_magic::use_attr;
+	// Because `derive_impl` is a [macro_magic](https://crates.io/crates/macro_magic) attribute
+	// macro, [`#[use_attr]`](`frame_support::macro_magic::use_attr`) must be attached to any use
+	// statement that brings it into scope.
+	#[use_attr]
+	use frame_support::derive_impl;
+
+	use super::pallet as pallet_default_config_example;
+
+	type UncheckedExtrinsic = frame_system::mocking::MockUncheckedExtrinsic<Test>;
+	type Block = frame_system::mocking::MockBlock<Test>;
+
+	frame_support::construct_runtime!(
+		pub enum Test where
+			Block = Block,
+			NodeBlock = Block,
+			UncheckedExtrinsic = UncheckedExtrinsic,
+		{
+			System: frame_system,
+			DefaultPallet: pallet_default_config_example,
+		}
+	);
+
+	#[derive_impl(frame_system::config_preludes::TestDefaultConfig as frame_system::DefaultConfig)]
+	impl frame_system::Config for Test {
+		// these items are defined by frame-system as `no_default`, so we must specify them here.
+		// Note that these are types that actually rely on the outer runtime, and can't sensibly
+		// have an _independent_ default.
+		type BaseCallFilter = frame_support::traits::Everything;
+		type RuntimeOrigin = RuntimeOrigin;
+		type RuntimeCall = RuntimeCall;
+		type RuntimeEvent = RuntimeEvent;
+		type PalletInfo = PalletInfo;
+		type OnSetCode = ();
+
+		// all of this is coming from `frame_system::config_preludes::TestDefaultConfig`.
+
+		// type Index = u32;
+		// type BlockNumber = u32;
+		// type Header = sp_runtime::generic::Header<Self::BlockNumber, Self::Hashing>;
+		// type Hash = sp_core::hash::H256;
+		// type Hashing = sp_runtime::traits::BlakeTwo256;
+		// type AccountId = u64;
+		// type Lookup = sp_runtime::traits::IdentityLookup<u64>;
+		// type BlockHashCount = frame_support::traits::ConstU32<10>;
+		// type MaxConsumers = frame_support::traits::ConstU32<16>;
+		// type AccountData = ();
+		// type OnNewAccount = ();
+		// type OnKilledAccount = ();
+		// type SystemWeightInfo = ();
+		// type SS58Prefix = ();
+		// type Version = ();
+		// type BlockWeights = ();
+		// type BlockLength = ();
+		// type DbWeight = ();
+
+		// you could still overwrite any of them if desired.
+		type SS58Prefix = frame_support::traits::ConstU16<456>;
+	}
+
+	// Similarly, we use the defaults provided by own crate as well.
+	use pallet::config_preludes::TestDefaultConfig;
+	#[derive_impl(TestDefaultConfig as pallet::DefaultConfig)]
+	impl crate::pallet::Config for Test {
+		// These two both cannot have defaults.
+		type RuntimeEvent = RuntimeEvent;
+		// Note that the default account-id type in
+		// `frame_system::config_preludes::TestDefaultConfig` is `u64`.
+		type CannotHaveDefault = frame_support::traits::ConstU64<1>;
+
+		type OverwrittenDefaultValue = frame_support::traits::ConstU32<678>;
+		type OverwrittenDefaultType = u128;
+	}
+
+	#[test]
+	fn it_works() {
+		use frame_support::traits::Get;
+		use pallet::{Config, DefaultConfig};
+
+		// assert one of the value types that is not overwritten.
+		assert_eq!(
+			<<Test as Config>::WithDefaultValue as Get<u32>>::get(),
+			<<TestDefaultConfig as DefaultConfig>::WithDefaultValue as Get<u32>>::get()
+		);
+
+		// assert one of the value types that is overwritten.
+		assert_eq!(<<Test as Config>::OverwrittenDefaultValue as Get<u32>>::get(), 678u32);
+
+		// assert one of the types that is not overwritten.
+		assert_eq!(
+			std::any::TypeId::of::<<Test as Config>::WithDefaultType>(),
+			std::any::TypeId::of::<<TestDefaultConfig as DefaultConfig>::WithDefaultType>()
+		);
+
+		// assert one of the types that is overwritten.
+		assert_eq!(
+			std::any::TypeId::of::<<Test as Config>::OverwrittenDefaultType>(),
+			std::any::TypeId::of::<u128>()
+		)
+	}
+}

frame/support/Cargo.toml

@@ -29,6 +29,7 @@ sp-staking = { version = "4.0.0-dev", default-features = false, path = "../../pr
 sp-weights = { version = "5.0.0", default-features = false, path = "../../primitives/weights" }
 sp-debug-derive = { default-features = false, path = "../../primitives/debug-derive" }
 tt-call = "1.0.8"
+macro_magic = "0.3.3"
 frame-support-procedural = { version = "4.0.0-dev", default-features = false, path = "./procedural" }
 paste = "1.0"
 once_cell = { version = "1", default-features = false, optional = true }

frame/support/procedural/Cargo.toml

@@ -24,6 +24,7 @@ quote = "1.0.26"
 syn = { version = "2.0.16", features = ["full"] }
 frame-support-procedural-tools = { version = "4.0.0-dev", path = "./tools" }
 proc-macro-warning = { version = "0.4.1", default-features = false }
+macro_magic = { version = "0.3.3", features = ["proc_support"] }
 
 [features]
 default = ["std"]

frame/support/procedural/src/construct_runtime/mod.rs

@@ -24,7 +24,7 @@
 //! `::{Call, ...}` or implicitly.
 //!
 //! In case a pallet defines its parts implicitly, then the pallet must provide the
-//! `tt_default_parts` macro. `construct_rutime` will generate some code which utilizes `tt_call`
+//! `tt_default_parts` macro. `construct_runtime` will generate some code which utilizes `tt_call`
 //! to call the `tt_default_parts` macro of the pallet. `tt_default_parts` will then return the
 //! default pallet parts as input tokens to the `match_and_replace` macro, which ultimately
 //! generates a call to `construct_runtime` again, this time with all the pallet parts explicitly