ACP: CStr::is_empty()

[jmillikin]

Proposal

Problem statement

The str and slice primitives both have is_empty() to check if a value is empty, but CStr currently doesn't. This is unfortunate because the CStr::to_bytes() function is documented as performing a length calculation in the future, which would make cstr_val.to_bytes().is_empty() into an O(N) operation.

Motivation, use-cases

There's many reasons a user might want to check if a C string is empty, for example when writing FFI bindings to code written in C that crashes if given an empty string.

Solution sketches

pub const fn is_empty(&self) -> bool {
    (unsafe { self.inner.get_unchecked(0) }) == &0
}

Links and related work

https://rust-for-linux.github.io/docs/kernel/str/struct.CStr.html#method.is_empty

What happens now?

This issue is part of the libs-api team API change proposal process. Once this issue is filed the libs-api team will review open proposals in its weekly meeting. You should receive feedback within a week or two.

[thomcc]

While I'm not sure about the specific implementation, this API seems worth adding.

[jmillikin]

Updated the solution sketch to be less sketch-y.

Proposed implementation: jmillikin/upstream__rust@29b261d

Docs screenshot:

[m-ou-se]

This briefly came up in the libs-api meetings. This looks fine to us. :)