It has been a while, but I remember a project of mine trying to port a FTP client to a 'secure compiler' (this was long before Rust and probably a distant ancestor of Checked C). In theory, if I could successfully port it, it would be much more resilient to particular kinds of issues (and maybe even attacks). This was in the era where formal proof coding was trying to take off as well in the industry.

After wading through an impressive number of compiler errors (again, it was technically compatible) and attempts to fix them, I eventually surrendered and acknowledged that at the very least, this was beyond my abilities.

I probably would had gotten much further just rewriting it from scratch.