Unifying anvil_reorg and anvil_rollback

[spalladino]

Looking into how to simulate reorgs in Anvil, I found two methods:

• anvil_reorg(depth, new_txs), implemented by @tsnewnami will rollback depth blocks, and create new ones in their place, optionally using txs provided.
• anvil_rollback(depth), implemented by @jorgemmsilva, will rollback depth blocks.

Aside from being quite similar, there is no method to reorg N blocks and add M blocks in their place (with N != M), since anvil_reorg will guarantee the block height is preserved.

Would it make sense to invest effort in unifying the two methods, and allowing to mine a customisable amount of blocks? So instead of having the following, where always depth new blocks are mined:

struct ReorgOptions {
    // The depth of the reorg
    pub depth: u64,
    // List of transaction requests and blocks pairs to be mined into the new chain
    pub tx_block_pairs: Vec<(TransactionData, u64)>,
}

Have something like:

struct ReorgOptions {
    // The depth of the reorg
    pub depth: u64,
    // List of blocks to be mined after the reorg, with the transactions for each block 
    pub new_blocks: Vec<Vec<TransactionData>>,
}

Assuming there is appetite for a change like this, would it be best to implement as a new method, or to break compatibility and replace the existing anvil_reorg?

[jorgemmsilva]

bonus points: fix the WS api, right now the eth_subscribe for newHeads won't properly communicate reorgs, as far as I can tell

[spalladino]

@jorgemmsilva that'd be great, but one step at a time. I'm waiting for green light from a maintainer before going forward!