Warning 7239 about assignment to storage array while it's being enlarged not issued when expansion happens inside a function

[nikola-matic]

Given the following reproduction scenario:

contract C {
    bytes public x;

    function _grow() private returns (bytes storage)  {
        x.push();
        return x;
    }

    function corrupt(bytes1 b) external {
        require(x.length == 31, "need len 31");
        (x[0], _grow()[1]) = (b, bytes1(0x00));
    }
}

the warning 7239 should be issued, however, this does not happen due to gaps in our static analysis, where we only perform such checks on direct .push() calls on storage pointers, and not much else. This should be improved so that indirect (i.e. from another function) array expansion is also covered.

[nikola-matic]

There's already a PR for this #16911.

[cameel]

By the way, @nikola-matic please make sure that the issue titles and descriptions have enough information to be understood without having to hunt for context. "Warning 7239" is too cryptic. I don't have all of them memorized :) For anyone wondering, it's this one:

This assignment involves multiple accesses to a bytes array in storage while simultaneously enlarging it. When a bytes array is enlarged, it may transition from short storage layout to long storage layout, which invalidates all references to its elements. It is safer to only enlarge byte arrays in a single operation, one element at a time.