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[improve docs]: Timestamp pallet (#1435)
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This PR improves the docs for the Timestamp pallet by following our
[Documentation
Guidelines](https://github.com/paritytech/polkadot-sdk/blob/master/docs/DOCUMENTATION_GUIDELINE.md)
more closely.

---------

Co-authored-by: Juan <juangirini@gmail.com>
Co-authored-by: Francisco Aguirre <franciscoaguirreperez@gmail.com>
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1 change: 1 addition & 0 deletions Cargo.lock
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33 changes: 16 additions & 17 deletions docs/DOCUMENTATION_GUIDELINE.md
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Expand Up @@ -123,9 +123,9 @@ explicitly depend on them, you have likely not designed it properly.

#### Proc-Macros

Note that there are special considerations when documenting proc macros. Doc links will appear to function _within_ your
Note that there are special considerations when documenting proc macros. Doc links will appear to function *within* your
proc macro crate, but often will no longer function when these proc macros are re-exported elsewhere in your project.
The exception is doc links to _other proc macros_ which will function just fine if they are also being re-exported. It
The exception is doc links to *other proc macros* which will function just fine if they are also being re-exported. It
is also often necessary to disambiguate between a proc macro and a function of the same name, which can be done using
the `macro@my_macro_name` syntax in your link. Read more about how to correctly use links in your rust-docs
[here](https://doc.rust-lang.org/rustdoc/write-documentation/linking-to-items-by-name.html#valid-links) and
Expand Down Expand Up @@ -189,6 +189,7 @@ fn multiply_by_2(x: u32) -> u32 { .. }
// More efficiency can be achieved if we improve this via such and such.
fn multiply_by_2(x: u32) -> u32 { .. }
```

They are both roughly conveying the same set of facts, but one is easier to follow because it was formatted cleanly.
Especially for traits and types that you can foresee will be seen and used a lot, try and write a well formatted
version.
Expand All @@ -203,7 +204,6 @@ properly do this.

---


## Pallet Crates

The guidelines so far have been general in nature, and are applicable to crates that are pallets and crates that're not
Expand All @@ -223,6 +223,14 @@ For the top-level pallet docs, consider the following template:
//!
//! <single-liner about the pallet>.
//!
//! ## Pallet API
//!
//! <Reminder: inside the [`pallet`] module, a template that leads the reader to the relevant items is auto-generated. There is no need to repeat
//! things like "See Config trait for ...", which are generated inside [`pallet`] here anyways. You can use the line below as-is:>
//!
//! See the [`pallet`] module for more information about the interfaces this pallet exposes, including its
//! configuration trait, dispatchables, storage items, events and errors.
//!
//! ## Overview
//!
//! <should be high-level details that are relevant to the most broad audience>
Expand All @@ -233,20 +241,12 @@ For the top-level pallet docs, consider the following template:
//!
//! ### Example
//!
//! <Your pallet must have a few tests that cover important user journeys. Use https://crates.io/crates/docify to reuse
//! these as examples>.
//! <Your pallet must have a few tests that cover important user journeys. Use https://crates.io/crates/docify to
//! reuse these as examples.>
//!
//! ## Pallet API
//!
//! <Reminder: inside the [`pallet`] module, a template that leads the reader to the relevant items is auto-generated.
//! There is no need to repeat things like "See Config trait for ...", which are generated inside [`pallet`] here anyways.
//! You can use the below line as-is:>
//!
//! See the [`pallet`] module for more information about the interfaces this pallet exposes, including its configuration
//! trait, dispatchables, storage items, events and errors.
//!
//! <The audience of this is those who want to know how this pallet works, to the extent of being able to build something
//! on top of it, like a DApp or another pallet>
//! <The audience of this is those who want to know how this pallet works, to the extent of being able to build
//! something on top of it, like a DApp or another pallet. In some cases, you might want to add an example of how to
//! use this pallet in other pallets.>
//!
//! This section can most often be left as-is.
//!
Expand All @@ -272,7 +272,6 @@ For the top-level pallet docs, consider the following template:
//! up>
```


This template's details (heading 3s and beyond) are left flexible, and at the discretion of the developer to make the
best final choice about. For example, you might want to include `### Terminology` or not. Moreover, you might find it
more useful to include it in `## Overview`.
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2 changes: 2 additions & 0 deletions substrate/frame/timestamp/Cargo.toml
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Expand Up @@ -27,6 +27,8 @@ sp-std = { path = "../../primitives/std", default-features = false}
sp-storage = { path = "../../primitives/storage", default-features = false}
sp-timestamp = { path = "../../primitives/timestamp", default-features = false}

docify = "0.2.1"

[dev-dependencies]
sp-core = { path = "../../primitives/core" }
sp-io = { path = "../../primitives/io" }
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162 changes: 104 additions & 58 deletions substrate/frame/timestamp/src/lib.rs
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Expand Up @@ -15,53 +15,40 @@
// See the License for the specific language governing permissions and
// limitations under the License.

//! # Timestamp Pallet
//!
//! The Timestamp pallet provides functionality to get and set the on-chain time.
//!
//! - [`Config`]
//! - [`Call`]
//! - [`Pallet`]
//!
//! ## Overview
//!
//! The Timestamp pallet allows the validators to set and validate a timestamp with each block.
//!
//! It uses inherents for timestamp data, which is provided by the block author and
//! validated/verified by other validators. The timestamp can be set only once per block and must be
//! set each block. There could be a constraint on how much time must pass before setting the new
//! timestamp.
//! > Made with *Substrate*, for *Polkadot*.
//!
//! **NOTE:** The Timestamp pallet is the recommended way to query the on-chain time instead of
//! using an approach based on block numbers. The block number based time measurement can cause
//! issues because of cumulative calculation errors and hence should be avoided.
//! [![github]](https://github.com/paritytech/polkadot-sdk/substrate/frame/timestamp)
//! [![polkadot]](https://polkadot.network)
//!
//! ## Interface
//! [polkadot]: https://img.shields.io/badge/polkadot-E6007A?style=for-the-badge&logo=polkadot&logoColor=white
//! [github]: https://img.shields.io/badge/github-8da0cb?style=for-the-badge&labelColor=555555&logo=github
//!
//! ### Dispatchable Functions
//!
//! * `set` - Sets the current time.
//!
//! ### Public functions
//! # Timestamp Pallet
//!
//! * `get` - Gets the current time for the current block. If this function is called prior to
//! setting the timestamp, it will return the timestamp of the previous block.
//! A pallet that provides a way for consensus systems to set and check the onchain time.
//!
//! ### Config Getters
//! ## Pallet API
//!
//! * `MinimumPeriod` - Gets the minimum (and advised) period between blocks for the chain.
//! See the [`pallet`] module for more information about the interfaces this pallet exposes,
//! including its configuration trait, dispatchables, storage items, events and errors.
//!
//! ## Overview
//!
//! ## Usage
//! The Timestamp pallet is designed to create a consensus-based time source. This helps ensure that
//! nodes maintain a synchronized view of time that all network participants can agree on.
//!
//! The following example shows how to use the Timestamp pallet in your custom pallet to query the
//! current timestamp.
//! It defines an _acceptable range_ using a configurable constant to specify how much time must
//! pass before setting the new timestamp. Validator nodes in the network must verify that the
//! timestamp falls within this acceptable range and reject blocks that do not.
//!
//! ### Prerequisites
//! > **Note:** The timestamp set by this pallet is the recommended way to query the onchain time
//! > instead of using block numbers alone. Measuring time with block numbers can cause cumulative
//! > calculation errors if depended upon in time critical operations and hence should generally be
//! > avoided.
//!
//! Import the Timestamp pallet into your custom pallet and derive the pallet configuration
//! trait from the timestamp trait.
//! ## Example
//!
//! ### Get current timestamp
//! To get the current time for the current block in another pallet:
//!
//! ```
//! use pallet_timestamp::{self as timestamp};
Expand All @@ -83,23 +70,60 @@
//! #[pallet::weight(0)]
//! pub fn get_time(origin: OriginFor<T>) -> DispatchResult {
//! let _sender = ensure_signed(origin)?;
//! let _now = <timestamp::Pallet<T>>::get();
//! let _now = timestamp::Pallet::<T>::get();
//! Ok(())
//! }
//! }
//! }
//! # fn main() {}
//! ```
//!
//! ### Example from the FRAME
//! If [`Pallet::get`] is called prior to setting the timestamp, it will return the timestamp of
//! the previous block.
//!
//! The [Session pallet](https://github.com/paritytech/substrate/blob/master/frame/session/src/lib.rs) uses
//! the Timestamp pallet for session management.
//! ## Low Level / Implementation Details
//!
//! ## Related Pallets
//! A timestamp is added to the chain using an _inherent extrinsic_ that only a block author can
//! submit. Inherents are a special type of extrinsic in Substrate chains that will always be
//! included in a block.
//!
//! * [Session](../pallet_session/index.html)
//! To provide inherent data to the runtime, this pallet implements
//! [`ProvideInherent`](frame_support::inherent::ProvideInherent). It will only create an inherent
//! if the [`Call::set`] dispatchable is called, using the
//! [`inherent`](frame_support::pallet_macros::inherent) macro which enables validator nodes to call
//! into the runtime to check that the timestamp provided is valid.
//! The implementation of [`ProvideInherent`](frame_support::inherent::ProvideInherent) specifies a
//! constant called `MAX_TIMESTAMP_DRIFT_MILLIS` which is used to determine the acceptable range for
//! a valid timestamp. If a block author sets a timestamp to anything that is more than this
//! constant, a validator node will reject the block.
//!
//! The pallet also ensures that a timestamp is set at the start of each block by running an
//! assertion in the `on_finalize` runtime hook. See [`frame_support::traits::Hooks`] for more
//! information about how hooks work.
//!
//! Because inherents are applied to a block in the order they appear in the runtime
//! construction, the index of this pallet in
//! [`construct_runtime`](frame_support::construct_runtime) must always be less than any other
//! pallet that depends on it.
//!
//! The [`Config::OnTimestampSet`] configuration trait can be set to another pallet we want to
//! notify that the timestamp has been updated, as long as it implements [`OnTimestampSet`].
//! Examples are the Babe and Aura pallets.
//! This pallet also implements [`Time`] and [`UnixTime`] so it can be used to configure other
//! pallets that require these types (e.g. in Staking pallet).
//!
//! ## Panics
//!
//! There are 3 cases where this pallet could cause the runtime to panic.
//!
//! 1. If no timestamp is set at the end of a block.
//!
//! 2. If a timestamp is set more than once per block:
#![doc = docify::embed!("src/tests.rs", double_timestamp_should_fail)]
//!
//! 3. If a timestamp is set before the [`Config::MinimumPeriod`] is elapsed:
#![doc = docify::embed!("src/tests.rs", block_period_minimum_enforced)]
#![deny(missing_docs)]
#![cfg_attr(not(feature = "std"), no_std)]

mod benchmarking;
Expand All @@ -123,10 +147,9 @@ pub mod pallet {
use frame_support::pallet_prelude::*;
use frame_system::pallet_prelude::*;

/// The pallet configuration trait
#[pallet::config]
pub trait Config: frame_system::Config {
/// Type used for expressing timestamp.
/// Type used for expressing a timestamp.
type Moment: Parameter
+ Default
+ AtLeast32Bit
Expand All @@ -135,14 +158,17 @@ pub mod pallet {
+ MaxEncodedLen
+ scale_info::StaticTypeInfo;

/// Something which can be notified when the timestamp is set. Set this to `()` if not
/// needed.
/// Something which can be notified (e.g. another pallet) when the timestamp is set.
///
/// This can be set to `()` if it is not needed.
type OnTimestampSet: OnTimestampSet<Self::Moment>;

/// The minimum period between blocks. Beware that this is different to the *expected*
/// period that the block production apparatus provides. Your chosen consensus system will
/// generally work with this to determine a sensible block time. e.g. For Aura, it will be
/// double this period on default settings.
/// The minimum period between blocks.
///
/// Be aware that this is different to the *expected* period that the block production
/// apparatus provides. Your chosen consensus system will generally work with this to
/// determine a sensible block time. For example, in the Aura pallet it will be double this
/// period on default settings.
#[pallet::constant]
type MinimumPeriod: Get<Self::Moment>;

Expand All @@ -153,23 +179,31 @@ pub mod pallet {
#[pallet::pallet]
pub struct Pallet<T>(_);

/// Current time for the current block.
/// The current time for the current block.
#[pallet::storage]
#[pallet::getter(fn now)]
pub type Now<T: Config> = StorageValue<_, T::Moment, ValueQuery>;

/// Did the timestamp get updated in this block?
/// Whether the timestamp has been updated in this block.
///
/// This value is updated to `true` upon successful submission of a timestamp by a node.
/// It is then checked at the end of each block execution in the `on_finalize` hook.
#[pallet::storage]
pub(super) type DidUpdate<T: Config> = StorageValue<_, bool, ValueQuery>;

#[pallet::hooks]
impl<T: Config> Hooks<BlockNumberFor<T>> for Pallet<T> {
/// dummy `on_initialize` to return the weight used in `on_finalize`.
/// A dummy `on_initialize` to return the amount of weight that `on_finalize` requires to
/// execute.
fn on_initialize(_n: BlockNumberFor<T>) -> Weight {
// weight of `on_finalize`
T::WeightInfo::on_finalize()
}

/// At the end of block execution, the `on_finalize` hook checks that the timestamp was
/// updated. Upon success, it removes the boolean value from storage. If the value resolves
/// to `false`, the pallet will panic.
///
/// ## Complexity
/// - `O(1)`
fn on_finalize(_n: BlockNumberFor<T>) {
Expand All @@ -185,13 +219,17 @@ pub mod pallet {
/// phase, if this call hasn't been invoked by that time.
///
/// The timestamp should be greater than the previous one by the amount specified by
/// `MinimumPeriod`.
/// [`Config::MinimumPeriod`].
///
/// The dispatch origin for this call must be _None_.
///
/// The dispatch origin for this call must be `Inherent`.
/// This dispatch class is _Mandatory_ to ensure it gets executed in the block. Be aware
/// that changing the complexity of this call could result exhausting the resources in a
/// block to execute any other calls.
///
/// ## Complexity
/// - `O(1)` (Note that implementations of `OnTimestampSet` must also be `O(1)`)
/// - 1 storage read and 1 storage mutation (codec `O(1)`). (because of `DidUpdate::take` in
/// - 1 storage read and 1 storage mutation (codec `O(1)` because of `DidUpdate::take` in
/// `on_finalize`)
/// - 1 event handler `on_timestamp_set`. Must be `O(1)`.
#[pallet::call_index(0)]
Expand All @@ -216,6 +254,14 @@ pub mod pallet {
}
}

/// To check the inherent is valid, we simply take the max value between the current timestamp
/// and the current timestamp plus the [`Config::MinimumPeriod`].
/// We also check that the timestamp has not already been set in this block.
///
/// ## Errors:
/// - [`InherentError::TooFarInFuture`]: If the timestamp is larger than the current timestamp +
/// minimum drift period.
/// - [`InherentError::TooEarly`]: If the timestamp is less than the current + minimum period.
#[pallet::inherent]
impl<T: Config> ProvideInherent for Pallet<T> {
type Call = Call<T>;
Expand Down Expand Up @@ -285,9 +331,9 @@ impl<T: Config> Pallet<T> {
}

impl<T: Config> Time for Pallet<T> {
/// A type that represents a unit of time.
type Moment = T::Moment;

/// Before the first set of now with inherent the value returned is zero.
fn now() -> Self::Moment {
Self::now()
}
Expand Down
2 changes: 2 additions & 0 deletions substrate/frame/timestamp/src/tests.rs
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Expand Up @@ -30,6 +30,7 @@ fn timestamp_works() {
});
}

#[docify::export]
#[test]
#[should_panic(expected = "Timestamp must be updated only once in the block")]
fn double_timestamp_should_fail() {
Expand All @@ -39,6 +40,7 @@ fn double_timestamp_should_fail() {
});
}

#[docify::export]
#[test]
#[should_panic(
expected = "Timestamp must increment by at least <MinimumPeriod> between sequential blocks"
Expand Down
2 changes: 1 addition & 1 deletion substrate/primitives/timestamp/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -140,7 +140,7 @@ pub enum InherentError {
error("The time since the last timestamp is lower than the minimum period.")
)]
TooEarly,
/// The block timestamp is too far in the future
/// The block timestamp is too far in the future.
#[cfg_attr(feature = "std", error("The timestamp of the block is too far in the future."))]
TooFarInFuture,
}
Expand Down

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