How does Cannon Barrage work with Warwick, specifically regarding the timing and interaction of their abilities?

Ruling: When Warwick attacks, his ability goes on the initial chain, then you can react with Cannon Barrage. Cannon Barrage resolves first dealing damage, then Warwick's ability kills all damaged enemy units, then combat damage is assigned.

Sequence:

• Warwick attacks and his ability goes on the initial chain
• You can react on top with Cannon Barrage
• Cannon Barrage resolves, dealing damage to all enemy units in combat
• Both players have opportunity to react again
• Warwick's ability resolves, killing all damaged enemy units
• Combat damage is assigned (if anything survives)

Nuances:

• Cannon Barrage only works when there are units in combat at battlefields; it does not work on showdowns at open battlefields
• After Cannon Barrage resolves, the opponent could play something like Shen to trade with Warwick