Derive Clone for EvmEnv

[intoverflow]

Why?

Imagine a situation where the host wants to generate multiple Steel proofs, all using the same RPC provider and block number. In this case, one might start by setting up an EthEvmEnv:

let env = EthEvmEnv::from_rpc(args.rpc_url, block_number).await?.with_chain_spec(chain_spec);

Later, each time we want to use Steel, we work from a fresh clone of env.

In this way, we can avoid passing the RPC and block number around (less verbose and maybe less error prone)

[Wollac]

With #91 we've introduced the ability to execute multiple calls using the same EvmEnv, so this feature would only be useful in a case where multiple independent Steel proofs (but still referencing the same block) are to be generated within the same host file.
I am a bit reluctant to make the env clonable, as this would also clone the underlying DB with all its current entries. This could lead to errors or misunderstandings as to whether the cloned envs have the same state or not.
If this is really a realistic use case, are there perhaps simple alternatives? Like maybe introducing an EnvBuilder?

[intoverflow]

You make some very good points. I will think some more and get back to you.

[intoverflow]

this feature would only be useful in a case where multiple independent Steel proofs (but still referencing the same block) are to be generated within the same host file

This is exactly the situation I'm in. Basically, I need to do a bunch of separate Steel proofs, which I then roll-up into one proof. Right now I'm doing something like this:

let env = EthEvmEnv::from_rpc(args.rpc_url, BlockNumberOrTag::Number(args.block_number)).await?.with_chain_spec(chain_spec);

...

let foo_receipt = foo(env.clone(), foo_args)?;
let bar_receipt = bar(env.clone(), bar_args)?;

...

This saves me from needing to pass the RPC url, block number, chain_spec.

A builder would be just as good for this purpose, and also (as you point out) would be less error prone. I'll close this PR and maybe we can make the builder happen this week