openzeppelin-contracts/certora/specs/GovernorStates.spec

import "helpers.spec"
import "methods/IGovernor.spec"
import "Governor.helpers.spec"
import "GovernorInvariants.spec"

use invariant proposalStateConsistency
use invariant votesImplySnapshotPassed

/*
┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Rule: state returns one of the value in the enumeration                                                             │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
*/
rule stateConsistency(env e, uint256 pId) {
    uint8 result = state(e, pId);
    assert (
        result == PENDING()   ||
        result == ACTIVE()    ||
        result == CANCELED()  ||
        result == DEFEATED()  ||
        result == SUCCEEDED() ||
        result == QUEUED()    ||
        result == EXECUTED()
    );
}

/*
┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Rule: State transitions caused by function calls                                                                    │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
*/
rule stateTransitionFn(uint256 pId, env e, method f, calldataarg args)
    filtered { f -> !skip(f) }
{
    require clockSanity(e);

    uint8 stateBefore = state(e, pId);
    f(e, args);
    uint8 stateAfter  = state(e, pId);

    assert (stateBefore != stateAfter) => (
        stateBefore == UNSET() => (
            stateAfter == PENDING() && f.selector == propose(address[],uint256[],bytes[],string).selector
        ) &&
        stateBefore == PENDING() => (
            (stateAfter == CANCELED() && f.selector == cancel(address[],uint256[],bytes[],bytes32).selector)
        ) &&
        stateBefore == SUCCEEDED() => (
            (stateAfter == QUEUED()   && f.selector == queue(address[],uint256[],bytes[],bytes32).selector) ||
            (stateAfter == EXECUTED() && f.selector == execute(address[],uint256[],bytes[],bytes32).selector)
        ) &&
        stateBefore == QUEUED() => (
            (stateAfter == EXECUTED() && f.selector == execute(address[],uint256[],bytes[],bytes32).selector)
        ) &&
        stateBefore == ACTIVE()    => false &&
        stateBefore == CANCELED()  => false &&
        stateBefore == DEFEATED()  => false &&
        stateBefore == EXECUTED()  => false
    );
}

/*
┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Rule: State transitions caused by time passing                                                                      │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
*/
rule stateTransitionWait(uint256 pId, env e1, env e2) {
    require clockSanity(e1);
    require clockSanity(e2);
    require clock(e2) > clock(e1);

    uint8 stateBefore = state(e1, pId);
    uint8 stateAfter  = state(e2, pId);

    assert (stateBefore != stateAfter) => (
        stateBefore == PENDING()   => stateAfter == ACTIVE() &&
        stateBefore == ACTIVE()    => (stateAfter == SUCCEEDED() || stateAfter == DEFEATED()) &&
        stateBefore == UNSET()     => false &&
        stateBefore == SUCCEEDED() => false &&
        stateBefore == QUEUED()    => false &&
        stateBefore == CANCELED()  => false &&
        stateBefore == DEFEATED()  => false &&
        stateBefore == EXECUTED()  => false
    );
}

/*
┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Rule: State corresponds to the vote timing and results                                                              │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
*/
rule stateIsConsistentWithVotes(uint256 pId, env e) {
    require clockSanity(e);
    requireInvariant proposalStateConsistency(pId);

    uint48  currentClock  = clock(e);
    uint8   currentState  = state(e, pId);
    uint256 snapshot      = proposalSnapshot(pId);
    uint256 deadline      = proposalDeadline(pId);
    bool    quorumSuccess = quorumReached(pId);
    bool    voteSuccess   = voteSucceeded(pId);

    // Pending: before vote starts
    assert currentState == PENDING() => (
        snapshot >= currentClock
    );

    // Active: after vote starts & before vote ends
    assert currentState == ACTIVE() => (
        snapshot < currentClock &&
        deadline >= currentClock
    );

    // Succeeded: after vote end, with vote successful and quorum reached
    assert currentState == SUCCEEDED() => (
        deadline < currentClock &&
        (
            quorumSuccess &&
            voteSuccess
        )
    );

    // Defeated: after vote end, with vote not successful or quorum not reached
    assert currentState == DEFEATED() => (
        deadline < currentClock &&
        (
            !quorumSuccess ||
            !voteSuccess
        )
    );
}

/*
┌─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ Rule: `updateQuorumNumerator` cannot cause quorumReached to change.                                                 │
└─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘
*/
rule onlyVoteCanChangeQuorumReached(uint256 pId, env e, method f, calldataarg args)
    filtered { f -> !skip(f) }
{
    require clockSanity(e);
    requireInvariant votesImplySnapshotPassed(e, pId);

    bool quorumReachedBefore = quorumReached(pId);

    uint256 snapshot    = proposalSnapshot(pId);
    uint256 totalSupply = token_getPastTotalSupply(snapshot);

    f(e, args);

    // Needed because the prover doesn't understand the checkpoint properties of the voting token.
    require clock(e) > snapshot => token_getPastTotalSupply(snapshot) == totalSupply;

    assert quorumReached(pId) != quorumReachedBefore => (
        !quorumReachedBefore &&
        votingAll(f)
    );
}