Governance: Votes (OpenZeppelin#552)

* init mod, fungible extension and example

* review votes

* add tests and fix docstrings

* add nft votes extension

* coverage

* avoid redundant event emission

* suggestions

* refactor with unified fns

* add total_supply in trait

* fix events

* get_checkpoint as pub with error instead default

Author: brozorec

Cargo.lock

@@ -5,6 +5,7 @@ members = [
     "examples/fungible-blocklist",
     "examples/fungible-capped",
     "examples/fungible-merkle-airdrop",
+    "examples/fungible-votes",
     "examples/fee-forwarder-permissioned",
     "examples/fee-forwarder-permissionless",
     "examples/fungible-pausable",

Cargo.toml

@@ -0,0 +1,21 @@
+[package]
+name = "fungible-votes-example"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+publish = false
+version.workspace = true
+
+[lib]
+crate-type = ["cdylib"]
+doctest = false
+
+[dependencies]
+soroban-sdk = { workspace = true }
+stellar-access = { workspace = true }
+stellar-governance = { workspace = true }
+stellar-macros = { workspace = true }
+stellar-tokens = { workspace = true }
+
+[dev-dependencies]
+soroban-sdk = { workspace = true, features = ["testutils"] }

examples/fungible-votes/Cargo.toml

@@ -0,0 +1,32 @@
+use soroban_sdk::{contract, contractimpl, Address, Env, MuxedAddress, String};
+use stellar_access::ownable::{set_owner, Ownable};
+use stellar_governance::votes::Votes;
+use stellar_macros::only_owner;
+use stellar_tokens::fungible::{votes::FungibleVotes, Base, FungibleToken};
+
+#[contract]
+pub struct ExampleContract;
+
+#[contractimpl]
+impl ExampleContract {
+    pub fn __constructor(e: &Env, owner: Address) {
+        Base::set_metadata(e, 7, String::from_str(e, "My Token"), String::from_str(e, "MTK"));
+        set_owner(e, &owner);
+    }
+
+    #[only_owner]
+    pub fn mint(e: &Env, to: &Address, amount: i128) {
+        FungibleVotes::mint(e, to, amount);
+    }
+}
+
+#[contractimpl(contracttrait)]
+impl FungibleToken for ExampleContract {
+    type ContractType = FungibleVotes;
+}
+
+#[contractimpl(contracttrait)]
+impl Votes for ExampleContract {}
+
+#[contractimpl(contracttrait)]
+impl Ownable for ExampleContract {}

examples/fungible-votes/src/contract.rs

@@ -0,0 +1,3 @@
+#![no_std]
+
+mod contract;

examples/fungible-votes/src/lib.rs

@@ -6,10 +6,30 @@ Stellar governance functionalities
 
 This package provides governance modules for Soroban smart contracts:
 
+- **Votes**: Vote tracking with delegation and historical checkpointing
 - **Timelock**: Time-delayed execution of operations
 
 ## Modules
 
+### Votes
+
+The `votes` module provides vote tracking functionality with delegation and historical checkpointing for governance mechanisms.
+
+#### Core Concepts
+
+- **Voting Units**: The base unit of voting power, typically 1:1 with token balance
+- **Delegation**: Accounts can delegate their voting power to another account (delegatee)
+- **Checkpoints**: Historical snapshots of voting power at specific timestamps
+- **Clock Mode**: Uses ledger timestamps (`e.ledger().timestamp()`) as the timepoint reference
+
+#### Key Features
+
+- Track voting power per account with historical checkpoints
+- Support delegation (an account can delegate its voting power to another account)
+- Provide historical vote queries at any past timestamp
+- Explicit delegation required (accounts must self-delegate to use their own voting power)
+- Non-delegated voting units are not counted as votes
+
 ### Timelock
 
 The `timelock` module provides functionality for time-delayed execution of operations, enabling governance mechanisms where actions must wait for a minimum delay before execution.

packages/governance/README.md

@@ -1,3 +1,4 @@
 #![no_std]
 
 pub mod timelock;
+pub mod votes;

packages/governance/src/lib.rs

@@ -0,0 +1,269 @@
+//! # Votes Module
+//!
+//! This module provides utilities for tracking voting power per account with
+//! historical checkpoints. It supports delegation (an account can delegate its
+//! voting power to another account) and provides historical vote queries at any
+//! past timestamp.
+//!
+//! # Core Concepts
+//!
+//! - **Voting Units**: The base unit of voting power, typically 1:1 with token
+//!   balance
+//! - **Delegation**: Accounts can delegate their voting power to another
+//!   account (delegatee). **Only delegated voting power counts as votes** while
+//!   undelegated voting units are not counted. Self-delegation is required for
+//!   an account to use its own voting power.
+//! - **Checkpoints**: Historical snapshots of voting power at specific
+//!   timestamps
+//!
+//! # Usage
+//!
+//! This module is to be integrated into a token contract and is responsible
+//! for:
+//! - Overriding the transfer method to call `transfer_voting_units` on every
+//!   balance change (mint/burn/transfer), as shown in the example below
+//! - Exposing delegation functionality to users
+//!
+//! # Example
+//!
+//! ```ignore
+//! use stellar_governance::votes::{
+//!     delegate, get_votes, get_votes_at_checkpoint, transfer_voting_units,
+//! };
+//!
+//! // Override your token contract's transfer to update voting units:
+//! pub fn transfer(e: &Env, from: Address, to: Address, amount: i128) {
+//!     // ... perform transfer logic ...
+//!     transfer_voting_units(e, Some(&from), Some(&to), amount as u128);
+//! }
+//!
+//! // Expose delegation:
+//! pub fn delegate(e: &Env, account: Address, delegatee: Address) {
+//!     votes::delegate(e, &account, &delegatee);
+//! }
+//! ```
+
+mod storage;
+
+#[cfg(test)]
+mod test;
+
+use soroban_sdk::{contracterror, contractevent, contracttrait, Address, Env};
+
+pub use crate::votes::storage::{
+    delegate, get_checkpoint, get_delegate, get_total_supply, get_total_supply_at_checkpoint,
+    get_votes, get_votes_at_checkpoint, get_voting_units, num_checkpoints, transfer_voting_units,
+    Checkpoint, CheckpointType, VotesStorageKey,
+};
+
+/// Trait for contracts that support vote tracking with delegation.
+///
+/// This trait defines the interface for vote tracking functionality.
+/// Contracts implementing this trait can be used in governance systems
+/// that require historical vote queries and delegation.
+///
+/// # Implementation Notes
+///
+/// The implementing contract must:
+/// - Call `transfer_voting_units` on every balance change
+/// - Expose `delegate` functionality to users
+#[contracttrait]
+pub trait Votes {
+    /// Returns the current voting power (delegated votes) of an account.
+    ///
+    /// Returns `0` if the account has no delegated voting power or does not
+    /// exist in the contract.
+    ///
+    /// # Arguments
+    ///
+    /// * `e` - Access to the Soroban environment.
+    /// * `account` - The address to query voting power for.
+    fn get_votes(e: &Env, account: Address) -> u128 {
+        get_votes(e, &account)
+    }
+
+    /// Returns the voting power (delegated votes) of an account at a specific
+    /// past timestamp.
+    ///
+    /// Returns `0` if the account had no delegated voting power at the given
+    /// timepoint or does not exist in the contract.
+    ///
+    /// # Arguments
+    ///
+    /// * `e` - Access to the Soroban environment.
+    /// * `account` - The address to query voting power for.
+    /// * `timepoint` - The timestamp to query (must be in the past).
+    ///
+    /// # Errors
+    ///
+    /// * [`VotesError::FutureLookup`] - If `timepoint` >= current timestamp.
+    fn get_votes_at_checkpoint(e: &Env, account: Address, timepoint: u64) -> u128 {
+        get_votes_at_checkpoint(e, &account, timepoint)
+    }
+
+    /// Returns the current total supply of voting units.
+    ///
+    /// This tracks all voting units in circulation (regardless of delegation
+    /// status), not just delegated votes.
+    ///
+    /// Returns `0` if no voting units exist.
+    ///
+    /// # Arguments
+    ///
+    /// * `e` - Access to the Soroban environment.
+    fn get_total_supply(e: &Env) -> u128 {
+        get_total_supply(e)
+    }
+
+    /// Returns the total supply of voting units at a specific past timestamp.
+    ///
+    /// This tracks all voting units in circulation (regardless of delegation
+    /// status), not just delegated votes.
+    ///
+    /// Returns `0` if there were no voting units at the given timepoint.
+    ///
+    /// # Arguments
+    ///
+    /// * `e` - Access to the Soroban environment.
+    /// * `timepoint` - The timestamp to query (must be in the past).
+    ///
+    /// # Errors
+    ///
+    /// * [`VotesError::FutureLookup`] - If `timepoint` >= current timestamp.
+    fn get_total_supply_at_checkpoint(e: &Env, timepoint: u64) -> u128 {
+        get_total_supply_at_checkpoint(e, timepoint)
+    }
+
+    /// Returns the current delegate for an account.
+    ///
+    /// # Arguments
+    ///
+    /// * `e` - Access to the Soroban environment.
+    /// * `account` - The address to query the delegate for.
+    ///
+    /// # Returns
+    ///
+    /// * `Some(Address)` - The delegate address if delegation is set.
+    /// * `None` - If the account has not delegated.
+    fn get_delegate(e: &Env, account: Address) -> Option<Address> {
+        get_delegate(e, &account)
+    }
+
+    /// Delegates voting power from `account` to `delegatee`.
+    ///
+    /// # Arguments
+    ///
+    /// * `e` - Access to the Soroban environment.
+    /// * `account` - The account delegating its voting power.
+    /// * `delegatee` - The account receiving the delegated voting power.
+    ///
+    /// # Events
+    ///
+    /// * topics - `["delegate_changed", delegator: Address]`
+    /// * data - `[from_delegate: Option<Address>, to_delegate: Address]`
+    ///
+    /// * topics - `["delegate_votes_changed", delegate: Address]`
+    /// * data - `[previous_votes: u128, new_votes: u128]`
+    ///
+    /// # Notes
+    ///
+    /// Authorization for `account` is required.
+    fn delegate(e: &Env, account: Address, delegatee: Address) {
+        delegate(e, &account, &delegatee);
+    }
+}
+// ################## ERRORS ##################
+
+/// Errors that can occur in votes operations.
+#[contracterror]
+#[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord)]
+#[repr(u32)]
+pub enum VotesError {
+    /// The timepoint is in the future
+    FutureLookup = 4100,
+    /// Arithmetic overflow occurred
+    MathOverflow = 4101,
+    /// Attempting to transfer more voting units than available
+    InsufficientVotingUnits = 4102,
+    /// Attempting to delegate to the same delegate that is already set
+    SameDelegate = 4103,
+    /// A checkpoint that was expected to exist was not found in storage
+    CheckpointNotFound = 4104,
+}
+
+// ################## CONSTANTS ##################
+
+const DAY_IN_LEDGERS: u32 = 17280;
+
+/// TTL extension amount for storage entries (in ledgers)
+pub const VOTES_EXTEND_AMOUNT: u32 = 30 * DAY_IN_LEDGERS;
+
+/// TTL threshold for extending storage entries (in ledgers)
+pub const VOTES_TTL_THRESHOLD: u32 = VOTES_EXTEND_AMOUNT - DAY_IN_LEDGERS;
+
+// ################## EVENTS ##################
+
+/// Event emitted when an account changes its delegate.
+#[contractevent]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct DelegateChanged {
+    /// The account that changed its delegate
+    #[topic]
+    pub delegator: Address,
+    /// The previous delegate (if any)
+    pub from_delegate: Option<Address>,
+    /// The new delegate
+    pub to_delegate: Address,
+}
+
+/// Emits an event when an account changes its delegate.
+///
+/// # Arguments
+///
+/// * `e` - Access to Soroban environment.
+/// * `delegator` - The account that changed its delegate.
+/// * `from_delegate` - The previous delegate (if any).
+/// * `to_delegate` - The new delegate.
+pub fn emit_delegate_changed(
+    e: &Env,
+    delegator: &Address,
+    from_delegate: Option<Address>,
+    to_delegate: &Address,
+) {
+    DelegateChanged {
+        delegator: delegator.clone(),
+        from_delegate,
+        to_delegate: to_delegate.clone(),
+    }
+    .publish(e);
+}
+
+/// Event emitted when a delegate's voting power changes.
+#[contractevent]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct DelegateVotesChanged {
+    /// The delegate whose voting power changed
+    #[topic]
+    pub delegate: Address,
+    /// The previous voting power
+    pub previous_votes: u128,
+    /// The new voting power
+    pub new_votes: u128,
+}
+
+/// Emits an event when a delegate's voting power changes.
+///
+/// # Arguments
+///
+/// * `e` - Access to Soroban environment.
+/// * `delegate` - The delegate whose voting power changed.
+/// * `previous_votes` - The previous voting power.
+/// * `new_votes` - The new voting power.
+pub fn emit_delegate_votes_changed(
+    e: &Env,
+    delegate: &Address,
+    previous_votes: u128,
+    new_votes: u128,
+) {
+    DelegateVotesChanged { delegate: delegate.clone(), previous_votes, new_votes }.publish(e);
+}