StableswapNGViews does not support get_dy_underlyinng for NG base pools

[bout3fiddy]

Description

To replicate:

boa.env.fork('https://eth.llamarpc.com')
metapool = boa.load_partial('./contracts/CurveStableSwapMetaNG.vy').at('0x9e10f9Fb6F0D32B350CEe2618662243d4f24C64a')
views = boa.load_partial('./contracts/CurveStableSwapNGViews.vy').at('0xe0B15824862f3222fdFeD99FeBD0f7e0EC26E1FA')
metapool.get_dy_underlying(1, 0, 50000000)

This returns the following error:

<Unknown location in unknown contract 383e6b4437b59fff47b619cba855ca29342a8559>

<./contracts/CurveStableSwapNGViews.vy at 0xe0B15824862f3222fdFeD99FeBD0f7e0EC26E1FA, compiled with vyper-0.3.10+9136169>
 <compiler: external call failed>
  contract "./contracts/CurveStableSwapNGViews.vy:464", function "_base_calc_token_amount", line 464:15 
       463         base_inputs[base_i] = dx
  ---> 464         return StableSwap2(base_pool).calc_token_amount(base_inputs, is_deposit)
  ------------------------^
       465
 <locals: dx=50000000, base_i=0, base_n_coins=2, base_pool=0x383E6b4437b59fff47B619CBA855CA29342A8559, is_deposit=True>

<./contracts/CurveStableSwapMetaNG.vy at 0x9e10f9Fb6F0D32B350CEe2618662243d4f24C64a, compiled with vyper-0.3.10+9136169>
<storage: stored_balances=[1400663115190697115437619, 390114779115648288603234], fee=4000000, offpeg_fee_multiplier=20000000000, initial_A=15000, future_A=15000, initial_A_time=0, future_A_time=0, admin_balances=[261077551664406060701, 283516149270762751715], last_prices_packed=347411840088524078890531743433958621136961216596013442290, last_D_packed=727366281545842402854317123229978519420754510210983088557039950, ma_exp_time=866, D_ma_time=62324, ma_last_time=581930941243133543360104174758465010551636275095, balanceOf={}, allowance={}, total_supply=1786431867672163347040320, nonces={}>
 <compiler: external call failed>
  contract "./contracts/CurveStableSwapMetaNG.vy:1719", function "get_dy_underlying", line 1719:11 
       1718     """
  ---> 1719     return StableSwapViews(factory.views_implementation()).get_dy_underlying(i, j, dx, self)
  ---------------------^
       1720
 <locals: i=1, j=0>

How to fix

Error exists in:

@internal
@view
def _base_calc_token_amount(
    dx: uint256,
    base_i: int128,
    base_n_coins: uint256,
    base_pool: address,
    is_deposit: bool
) -> uint256:

    if base_n_coins == 2:

        base_inputs: uint256[2] = empty(uint256[2])
        base_inputs[base_i] = dx
        return StableSwap2(base_pool).calc_token_amount(base_inputs, is_deposit)

    elif base_n_coins == 3:

        base_inputs: uint256[3] = empty(uint256[3])
        base_inputs[base_i] = dx
        return StableSwap3(base_pool).calc_token_amount(base_inputs, is_deposit)

    else:

        base_inputs: DynArray[uint256, MAX_COINS] = empty(DynArray[uint256, MAX_COINS])
        for i in range(base_n_coins, bound=MAX_COINS):
            if i == convert(base_i, uint256):
                base_inputs.append(dx)
            else:
                base_inputs.append(0)
        return StableSwapNG(base_pool).calc_token_amount(base_inputs, is_deposit)

base_n_coins can be equal to 2 but it is still an NG pool. So the branching is off. The correct if-else statement should should be:

base_pool_is_ng: bool = raw_call(_base_pool, method_id("D_ma_time()"), revert_on_failure=False)

if base_n_coins == 2 and not base_pool_is_ng:

    base_inputs: uint256[2] = empty(uint256[2])
    base_inputs[base_i] = dx
    return StableSwap2(base_pool).calc_token_amount(base_inputs, is_deposit)

elif base_n_coins == 3 and not base_pool_is_ng:

    base_inputs: uint256[3] = empty(uint256[3])
    base_inputs[base_i] = dx
    return StableSwap3(base_pool).calc_token_amount(base_inputs, is_deposit)

else:

Task list

Since the fix is only for views contract, and each AMM references the address of the views contract stored in the factory, the fix for all pools is in the factory contract (by design):

• Fix method and deploy new views implementation across all chains
• create dao vote for governance to accept new views implementation via: factory.set_views_implementation(new_implementation)
• Execute vote and let integrators know it has been fixed.