seal: code_hash queries

[pepyakin]

It might be useful to allow contracts to query their own code_hash. One thing that this would allow is to create contracts with identical codes.

Another possibility is to allow contracts to query code_hash of another contract specified by some address.

These two are not required for MVP and they are also not interdependent and can be delivered separately.

[gui1117]

Another possibility is to allow contracts to query code_hash of another contract specified by some address.

This is interesting for a contract to be able to trust another contract. For example a cookie-contract that is only writtable by a erc20 contract. The account will say to erc20 hello I want to use you and this is my cooke-contract, and erc20 will store the data he wants to store in this one and trusting by its code_hash.

Although this mecanism is not entirely needed due to CREATE2 properties because the address of a contract contains the code_hash, user and input_data so user can just say hello use this contract, it has been created by him with that input.
But we might not want to rely on CREATE2 properties.

[pepyakin]

Good point on CREATE2. However, I believe that code_hash query still provide at least some benefits:

1. As I mentioned in the first comment, code_hash query of the caller gives an ability to create instances with the same code that the caller has. Otherwise, the caller would have to have code_hash embedded as a literal but this might be not feasible.
2. Proofing that a contract has a certain address becomes more straightforward: you don't have to provide the caller address and data used to compute the address, you just compare hashes.
3. A code_hash query can tell whether a given address is a regular account (i.e. its code_hash is null) whereas CREATE2 can only proof that a particular address is a contract.

[stale]

Hey, is anyone still working on this? Due to the inactivity this issue has been automatically marked as stale. It will be closed if no further activity occurs. Thank you for your contributions.