Why does the creationCode of this contract change if a change is made in the importing contract?

Question

For the following:

pragma solidity >=0.5.0;

contract Include {
    uint z = 1;
}

contract CreationCode {
    uint k = 1;
    function get() external returns (bytes32) {
        return keccak256(type(Include).creationCode);
    }
}

why does creationCode for Include.sol change when changing k, which is not a variable in Include.sol?

Answer 1

By default, solc will embed a hash of compilation metadata in the generated bytecode. For the details see the solidity documentation. The source code's hash is included in the compiled metadata so a change in the source code will affect the metadata and bytecode generated.

One solution is to have Include in a separate file from CreationCode and import it when needed so any change to CreationCode will not affect Include's bytecode.