fix(balancer): Support ComposableStablePools on SwapAdapter.

Add support for CSP pools. The main issue here was that Limits for BPT tokens would be too high since the pool has the complete supply of the token preminted.

Not quite sure if the limit for buying the BPT token is set correctly but I guess you can try to buy the whole supply.

evm/src/balancer-v2/BalancerV2SwapAdapter.sol

@@ -169,19 +169,62 @@ contract BalancerV2SwapAdapter is ISwapAdapter {
         returns (uint256[] memory limits)
     {
         limits = new uint256[](2);
+        address pool;
+        (pool,) = vault.getPool(poolId);
+        uint256 bptIndex = maybeGetBptTokenIndex(pool);
+        uint256 circulatingSupply = getBptCirculatingSupply(pool);
+
         (address[] memory tokens, uint256[] memory balances,) =
             vault.getPoolTokens(poolId);
 
         for (uint256 i = 0; i < tokens.length; i++) {
             if (tokens[i] == sellToken) {
+                if (i == bptIndex) {
+                    // Some pools pre-mint the bpt tokens and keep the balance
+                    // on the
+                    // pool we can't sell more than the circulating supply
+                    // though,
+                    // else we get an underflow error.
+                    limits[0] = circulatingSupply;
+                } else {
                     limits[0] = balances[i] * RESERVE_LIMIT_FACTOR / 10;
                 }
+            }
             if (tokens[i] == buyToken) {
                 limits[1] = balances[i] * RESERVE_LIMIT_FACTOR / 10;
             }
         }
     }
 
+    function maybeGetBptTokenIndex(address poolAddress)
+        internal
+        view
+        returns (uint256)
+    {
+        IPool pool = IPool(poolAddress);
+
+        try pool.getBptIndex() returns (uint256 index) {
+            return index;
+        } catch {
+            return type(uint256).max;
+        }
+    }
+
+    function getBptCirculatingSupply(address poolAddress)
+        internal
+        view
+        returns (uint256)
+    {
+        IPool pool = IPool(poolAddress);
+        try pool.getActualSupply() returns (uint256 supply) {
+            return supply;
+        } catch {}
+        try pool.getVirtualSupply() returns (uint256 supply) {
+            return supply;
+        } catch {}
+        return type(uint256).max;
+    }
+
     function getCapabilities(bytes32, address, address)
         external
         pure
@@ -486,3 +529,11 @@ interface IVault {
         GIVEN_OUT
     }
 }
+
+interface IPool {
+    function getBptIndex() external view returns (uint256);
+
+    function getActualSupply() external view returns (uint256);
+
+    function getVirtualSupply() external view returns (uint256);
+}