feat(forge flatten): add dead code elimination

[sakulstra]

Component

Forge

Describe the feature you would like

When using some libraries, the --flatten output will be gigantic as flatten will inline all imports. It would be neat if flatten would detect & remove unused imports.

When using re-export index files like here https://github.com/bgd-labs/aave-address-book/blob/main/src/AaveAddressBook.sol that makes it essentially impossible to use in foundry as the generated code will be unusable long.

Additional context

In addition to what i mentioned above i guess it might make sense to even eliminate unused code in the actually imported files. Not sure sure about this though.

[gakonst]

Good catch.

[sakulstra]

@gakonst just realized the same is true for non flattened files.

When you have a file like:

// index.sol
import {A} from "a.sol";
import {B} from "b.sol";
import {C} from "c.sol";

// contract.sol
import {A, B} from "index.sol";

contract Contract {
  function test() public {
    A.noop();
  }
}

When I verify this contract it will include A, B and C although only A is used.

[gakonst]

We'd need to do deeper parsing of the dependency graph for this kind of flattening I think?

[pegahcarter]

It's probably worth an additional flag as the automatic removal of unused imports may confuse some developers.

I believe this would be a valuable feature as we'll see more utility in index files, as shown by protocols in addition to aave.

The dependency graph only grows as protocols build across many chains, requiring index files.