Accumulated subgraph rewards reset to zero on edge case

[abarmat]

Description

The RewardsManager contract main responsibility is to calculate rewards accrued for allocations based on the total token supply, tokens signalled on subgraphs, accumulated rewards on a subgraph and allocations. Under certain edge condition the calculation could fail and block closing an allocation that would collect rewards.

Problem

There is a particular edge case that happens when there are running allocations on a subgraph deployment ID, the total amount of curation signal is removed back to zero and closeAllocation() is called by an indexer. If this happens, the indexer won't be able to close that allocation unless it is opting for no rewards by sending POI=0x0. The reason for this is that getAccRewardsForSubgraph() is reseting the accumulated rewards for a subgraph when the curation pool is empty. The consequence is that subgraph.accRewardsForSubgraphSnapshot can be larger than subgraph.accRewardsForSubgraph leading to a revert when calculating new accrued rewards.

Solution

By removing the early check within getAccRewardsForSubgraph() that returns zero for the subgraph accumulated rewards when the signal is zero we will always return the accumulated amount, as it should be an ever increasing number.

Additional Changes

• Check that rewards > 0 before minting
• Linting differences
• Improve some comments

[abarmat]

Rebased