Warn for use of RawFd or AsRawFd in public interfaces

What it does

RFC 3128 adds AsFd, OwnedFd and BorrowedFd, which are much safer ways to handle file access than AsRawFd and RawFd. They're what Rust ideally would've done from the start. And now that they're in stable Rust there is little reason to use RawFd anymore. I suggest that Clippy warn when safe functions, especially public ones, use RawFd or AsRawFd in their signatures.

https://rust-lang.github.io/rfcs/3128-io-safety.html

Lint Name

rawfd_interface

Category

suspicious

Advantage

Prevents bugs caused by invalid file descriptors and use-after-close.

Drawbacks

• Requires a recent MSRV (1.63.0)
• For crates in the middle of the application stack, it may not be possible to convert them to use I/O Safety before lower-level crates do.

Example

pub fn do_some_io<FD: AsRawFd>(input: &FD) -> io::Result<()> {
    some_syscall(input.as_raw_fd())
}

Could be written as:

pub fn do_some_io<FD: AsFd>(input: &FD) -> io::Result<()> {
    some_syscall(input.as_fd())
}

Start with RFC 3128 and the issue's RawFd/AsRawFd example. Define the rawfd_interface lint so safe function signatures, especially public ones, warn when they use RawFd or AsRawFd, while recognizing the stated MSRV and migration constraints. Done when the lint behavior and its replacement guidance are covered for the proposed cases.