feat/multicall

[banteg]

What I did

Added multicall context manager I initially outlined here.

Related issue: #1011

How I did it

I used Multicall2 and wrapt library to replace results with proxies which are updated with actual values as soon as they are available.

Special thanks to @nymmrx for help with value wrappers.

How to verify it

Here is a complex example:

from brownie import *
import pandas as pd

def curve():
    curve_registry = Contract("0x7D86446dDb609eD0F5f8684AcF30380a356b2B4c")
    voter_proxy = Contract("0xF147b8125d2ef93FB6965Db97D6746952a133934")
    gauge_controller = Contract("0x2F50D538606Fa9EDD2B11E2446BEb18C9D5846bB")
    
    pool_count = curve_registry.pool_count()  # call 1
    with multicall() as caller:  # call 2
        pools = [caller(curve_registry).pool_list(i) for i in range(pool_count)]
    
    with multicall() as caller:  # call 3
        gauges = [caller(curve_registry).get_gauges(pool) for pool in pools]
    
    pools = [
        {'pool': Contract(pool), 'gauge': Contract(gauge[0][0])}
        for pool, gauge in zip(pools, gauges) if gauge[0][0] != ZERO_ADDRESS
    ]
    
    with multicall() as caller:  # call 4
        for pool in pools:
            pool['last_vote'] = caller(gauge_controller).last_user_vote(voter_proxy, pool['gauge'])
            pool['last_weight'] = caller(gauge_controller).vote_user_slopes(voter_proxy, pool['gauge'])
            pool['balance'] = caller(pool['gauge']).balanceOf(voter_proxy)
            pool['working_balance'] = caller(pool['gauge']).working_balances(voter_proxy)
            pool['virtual_price'] = caller(pool['pool']).get_virtual_price()

    for pool in pools:
        pool['last_weight'] = pool['last_weight'].dict()['power']
        pool['boost'] = pool['working_balance'] / pool['balance'] * 2.5 if pool['balance'] > 0 else 0
        pool['balance'] /= 1e18  # NOTE: all curve LP tokens have 18 decimals
        pool['virtual_price'] /= 1e18

    print(pd.DataFrame(pools)[['last_vote', 'last_weight', 'balance', 'boost', 'virtual_price']])

Checklist

• I have confirmed that my PR passes all linting checks
• I have included test cases
• I have updated the documentation
• I have added an entry to the changelog

[omarish]

Suggestion: make this a default kwarg for multicall so it's not hard-coded in the framework?

@contextmanager
def multicall(block_identifier=None, multicall2_address="0x5BA1e12693Dc8F9c48aAD8770482f4739bEeD696"):
    ...
    multicall2 = Contract(multicall2_address)

[banteg]

I was thinking to make it even more flexible:

• live network => use eth_call code override to make it available pre-deploy
• dev network => seamlessly deploy a contract and cache it

[nymmrx]

I think eth_call code override should be optional as some providers don't support them (e.g. infura)

[iamdefinitelyahuman]

Handled in #1125