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[improve docs]: Template pallet (#1280)

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* add and refactor docs

* commit mistake

* improvements

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* Apply suggestions from code review

Co-authored-by: Squirrel <gilescope@gmail.com>

* 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 <gilescope@gmail.com>
This commit is contained in:
Sacha Lansky
2023-09-02 02:34:46 +02:00
committed by GitHub
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commit 8cfaad4600
1 changed files with 126 additions and 30 deletions
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substrate/bin/node-template/pallets/template/src/lib.rs
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//! # 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(())
},
}