lint on `libc::strlen(some_cstr.as_ptr())`

[joshtriplett]

What it does

This lint would flag the use of libc::strlen on a CString or CStr value, and suggest calling to_bytes().len() instead.

Categories (optional)

• Kind: clippy::complexity

What is the advantage of the recommended code over the original code

This avoids calling an unsafe libc function. Currently, it also avoids calculating the length; in the future, this may become equivalent to calling strlen at runtime, but it'll still avoid the need for an unsafe libc call.

Drawbacks

None.

Example

libc::strlen(name.as_ptr())

Could be written as:

name.to_bytes().len()

[joshtriplett]

Inspired by rust-lang/rust#84589 (comment)

[mgacek8]

What about for CString suggesting as_bytes().len() instead of to_bytes().len() ?
as_bytes() shouldn't calculate the length in the future.

[joshtriplett]

@mgacek8 That seems reasonable, yes. The lint should apply to either CStr or CString; the suggested replacement can be different for the two.

[mgacek8]

I'll give it a shot.
@rustbot claim