[improve docs]: Template pallet (paritytech#1280)

* add and refactor docs

* commit mistake

* improvements

* fixes

* Apply suggestions from code review

Co-authored-by: Squirrel <[email protected]>

* fix: use markdown syntax

* from review: explain what generate_deposit does

* from review: add note about errors

* updates

* fix: bring back getter

---------

Co-authored-by: Squirrel <[email protected]>

Author: Sacha Lansky

substrate/bin/node-template/pallets/template/src/lib.rs

@@ -1,105 +1,201 @@
+//! # Template Pallet
+//!
+//! A pallet with minimal functionality to help developers understand the essential components of
+//! writing a FRAME pallet. It is typically used in beginner tutorials or in Substrate template
+//! nodes as a starting point for creating a new pallet and **not meant to be used in production**.
+//!
+//! ## Overview
+//!
+//! This template pallet contains basic examples of:
+//! - declaring a storage item that stores a single `u32` value
+//! - declaring and using events
+//! - declaring and using errors
+//! - a dispatchable function that allows a user to set a new value to storage and emits an event
+//!   upon success
+//! - another dispatchable function that causes a custom error to be thrown
+//!
+//! Each pallet section is annotated with an attribute using the `#[pallet::...]` procedural macro.
+//! This macro generates the necessary code for a pallet to be aggregated into a FRAME runtime.
+//!
+//! Learn more about FRAME macros [here](https://docs.substrate.io/reference/frame-macros/).
+//!
+//! ### Pallet Sections
+//!
+//! The pallet sections in this template are:
+//!
+//! - A **configuration trait** that defines the types and parameters which the pallet depends on
+//!   (denoted by the `#[pallet::config]` attribute). See: [`Config`].
+//! - A **means to store pallet-specific data** (denoted by the `#[pallet::storage]` attribute).
+//!   See: [`storage_types`].
+//! - A **declaration of the events** this pallet emits (denoted by the `#[pallet::event]`
+//!   attribute). See: [`Event`].
+//! - A **declaration of the errors** that this pallet can throw (denoted by the `#[pallet::error]`
+//!   attribute). See: [`Error`].
+//! - A **set of dispatchable functions** that define the pallet's functionality (denoted by the
+//!   `#[pallet::call]` attribute). See: [`dispatchables`].
+//!
+//! Run `cargo doc --package pallet-template --open` to view this pallet's documentation.
+
+// We make sure this pallet uses `no_std` for compiling to Wasm.
 #![cfg_attr(not(feature = "std"), no_std)]
 
-/// Edit this file to define custom logic or remove it if it is not needed.
-/// Learn more about FRAME and the core library of Substrate FRAME pallets:
-/// <https://docs.substrate.io/reference/frame-pallets/>
+// Re-export pallet items so that they can be accessed from the crate namespace.
 pub use pallet::*;
 
+// FRAME pallets require their own "mock runtimes" to be able to run unit tests. This module
+// contains a mock runtime specific for testing this pallet's functionality.
 #[cfg(test)]
 mod mock;
 
+// This module contains the unit tests for this pallet.
+// Learn about pallet unit testing here: https://docs.substrate.io/test/unit-testing/
 #[cfg(test)]
 mod tests;
 
+// Every callable function or "dispatchable" a pallet exposes must have weight values that correctly
+// estimate a dispatchable's execution time. The benchmarking module is used to calculate weights
+// for each dispatchable and generates this pallet's weight.rs file. Learn more about benchmarking here: https://docs.substrate.io/test/benchmark/
 #[cfg(feature = "runtime-benchmarks")]
 mod benchmarking;
 pub mod weights;
 pub use weights::*;
 
+// All pallet logic is defined in its own module and must be annotated by the `pallet` attribute.
 #[frame_support::pallet]
 pub mod pallet {
+	// Import various useful types required by all FRAME pallets.
 	use super::*;
 	use frame_support::pallet_prelude::*;
 	use frame_system::pallet_prelude::*;
 
+	// The `Pallet` struct serves as a placeholder to implement traits, methods and dispatchables
+	// (`Call`s) in this pallet.
 	#[pallet::pallet]
 	pub struct Pallet<T>(_);
 
-	/// Configure the pallet by specifying the parameters and types on which it depends.
+	/// The pallet's configuration trait.
+	///
+	/// All our types and constants a pallet depends on must be declared here.
+	/// These types are defined generically and made concrete when the pallet is declared in the
+	/// `runtime/src/lib.rs` file of your chain.
 	#[pallet::config]
 	pub trait Config: frame_system::Config {
-		/// Because this pallet emits events, it depends on the runtime's definition of an event.
+		/// The overarching runtime event type.
 		type RuntimeEvent: From<Event<Self>> + IsType<<Self as frame_system::Config>::RuntimeEvent>;
-		/// Type representing the weight of this pallet
+		/// A type representing the weights required by the dispatchables of this pallet.
 		type WeightInfo: WeightInfo;
 	}
 
-	// The pallet's runtime storage items.
-	// https://docs.substrate.io/main-docs/build/runtime-storage/
+	/// A storage item for this pallet.
+	///
+	/// In this template, we are declaring a storage item called `Something` that stores a single
+	/// `u32` value. Learn more about runtime storage here: <https://docs.substrate.io/build/runtime-storage/>
+	/// The [`getter`] macro generates a function to conveniently retrieve the value from storage.
 	#[pallet::storage]
 	#[pallet::getter(fn something)]
-	// Learn more about declaring storage items:
-	// https://docs.substrate.io/main-docs/build/runtime-storage/#declaring-storage-items
 	pub type Something<T> = StorageValue<_, u32>;
 
-	// Pallets use events to inform users when important changes are made.
-	// https://docs.substrate.io/main-docs/build/events-errors/
+	/// Events that functions in this pallet can emit.
+	///
+	/// Events are a simple means of indicating to the outside world (such as dApps, chain explorers
+	/// or other users) that some notable update in the runtime has occurred. In a FRAME pallet, the
+	/// documentation for each event field and its parameters is added to a node's metadata so it
+	/// can be used by external interfaces or tools.
+	///
+	///	The `generate_deposit` macro generates a function on `Pallet` called `deposit_event` which
+	/// will convert the event type of your pallet into `RuntimeEvent` (declared in the pallet's
+	/// [`Config`] trait) and deposit it using [`frame_system::Pallet::deposit_event`].
 	#[pallet::event]
 	#[pallet::generate_deposit(pub(super) fn deposit_event)]
 	pub enum Event<T: Config> {
-		/// Event documentation should end with an array that provides descriptive names for event
-		/// parameters. [something, who]
-		SomethingStored { something: u32, who: T::AccountId },
+		/// A user has successfully set a new value.
+		SomethingStored {
+			/// The new value set.
+			something: u32,
+			/// The account who set the new value.
+			who: T::AccountId,
+		},
 	}
 
-	// Errors inform users that something went wrong.
+	/// Errors that can be returned by this pallet.
+	///
+	/// Errors tell users that something went wrong so it's important that their naming is
+	/// informative. Similar to events, error documentation is added to a node's metadata so it's
+	/// equally important that they have helpful documentation associated with them.
+	///
+	/// This type of runtime error can be up to 4 bytes in size should you want to return additional
+	/// information.
 	#[pallet::error]
 	pub enum Error<T> {
-		/// Error names should be descriptive.
+		/// The value retrieved was `None` as no value was previously set.
 		NoneValue,
-		/// Errors should have helpful documentation associated with them.
+		/// There was an attempt to increment the value in storage over `u32::MAX`.
 		StorageOverflow,
 	}
 
-	// Dispatchable functions allows users to interact with the pallet and invoke state changes.
-	// These functions materialize as "extrinsics", which are often compared to transactions.
-	// Dispatchable functions must be annotated with a weight and must return a DispatchResult.
+	/// The pallet's dispatchable functions ([`Call`]s).
+	///
+	/// Dispatchable functions allows users to interact with the pallet and invoke state changes.
+	/// These functions materialize as "extrinsics", which are often compared to transactions.
+	/// They must always return a `DispatchResult` and be annotated with a weight and call index.
+	///
+	/// The [`call_index`] macro is used to explicitly
+	/// define an index for calls in the [`Call`] enum. This is useful for pallets that may
+	/// introduce new dispatchables over time. If the order of a dispatchable changes, its index
+	/// will also change which will break backwards compatibility.
+	///
+	/// The [`weight`] macro is used to assign a weight to each call.
 	#[pallet::call]
 	impl<T: Config> Pallet<T> {
-		/// An example dispatchable that takes a singles value as a parameter, writes the value to
-		/// storage and emits an event. This function must be dispatched by a signed extrinsic.
+		/// An example dispatchable that takes a single u32 value as a parameter, writes the value
+		/// to storage and emits an event.
+		///
+		/// It checks that the _origin_ for this call is _Signed_ and returns a dispatch
+		/// error if it isn't. Learn more about origins here: <https://docs.substrate.io/build/origins/>
 		#[pallet::call_index(0)]
 		#[pallet::weight(T::WeightInfo::do_something())]
 		pub fn do_something(origin: OriginFor<T>, something: u32) -> DispatchResult {
 			// Check that the extrinsic was signed and get the signer.
-			// This function will return an error if the extrinsic is not signed.
-			// https://docs.substrate.io/main-docs/build/origins/
 			let who = ensure_signed(origin)?;
 
 			// Update storage.
-			<Something<T>>::put(something);
+			Something::<T>::put(something);
 
 			// Emit an event.
 			Self::deposit_event(Event::SomethingStored { something, who });
-			// Return a successful DispatchResultWithPostInfo
+
+			// Return a successful `DispatchResult`
 			Ok(())
 		}
 
 		/// An example dispatchable that may throw a custom error.
+		///
+		/// It checks that the caller is a signed origin and reads the current value from the
+		/// `Something` storage item. If a current value exists, it is incremented by 1 and then
+		/// written back to storage.
+		///
+		/// ## Errors
+		///
+		/// The function will return an error under the following conditions:
+		///
+		/// - If no value has been set ([`Error::NoneValue`])
+		/// - If incrementing the value in storage causes an arithmetic overflow
+		///   ([`Error::StorageOverflow`])
 		#[pallet::call_index(1)]
 		#[pallet::weight(T::WeightInfo::cause_error())]
 		pub fn cause_error(origin: OriginFor<T>) -> DispatchResult {
 			let _who = ensure_signed(origin)?;
 
 			// Read a value from storage.
-			match <Something<T>>::get() {
+			match Pallet::<T>::something() {
 				// Return an error if the value has not been set.
 				None => Err(Error::<T>::NoneValue.into()),
 				Some(old) => {
-					// Increment the value read from storage; will error in the event of overflow.
+					// Increment the value read from storage. This will cause an error in the event
+					// of overflow.
 					let new = old.checked_add(1).ok_or(Error::<T>::StorageOverflow)?;
 					// Update the value in storage with the incremented result.
-					<Something<T>>::put(new);
+					Something::<T>::put(new);
 					Ok(())
 				},
 			}