Why does Forge generate a "src" folder in the "out" folder?

[PaulRBerg]

I am importing and inheriting from OpenZeppelin's ERC721 implementation, like this:

import { ERC721 } from "@openzeppelin/contracts/token/ERC721/ERC721.sol";

contract MyContract is ERC721 { }

By simply doing this, I get an additional src folder generated in the out folder after running forge build:

Why is that?

I did expect the output folder to contain the ABI for the Address utility from OpenZeppelin, but I do not understand why it is placed in src/utils folder in the out folder.

I did another test in a repo with a clean slate (my foundry-template) where I re-wrote the Foo contract like this:

pragma solidity >=0.8.4;

import { ERC721 } from "@openzeppelin/contracts/token/ERC721/ERC721.sol";

abstract contract Foo is ERC721 {}

Yet again, a src folder was generated in out, but now there wasn't the Address in there, but rather the Vm and VmSafe interfaces:

In both cases, I would have expected the ABIs found in src to be at the same level with the other ABIs.