Lint suggestion for Cow::to_ptr

[mulimoen]

What it does

Checks for temporary Cow immediately dereferenced

Categories (optional)

• Kind: clippy::correctness

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

The original code will produce a dangling pointer on a Cow::Owned if created as a function argument. This is the same situation as for CString which will lead to a use-after-free.

Drawbacks

None.

Example

use std::borrow::Cow;

fn take_ptr(_p: *const i32) { }

fn main() {
    take_ptr(Cow::<[i32]>::Owned(vec![0]).as_ptr());
    take_ptr(Cow::<[i32]>::Borrowed(&[1]).as_ptr());
}

Could be written as:

use std::borrow::Cow;

fn take_ptr(_p: *const i32) { }

fn main() {
    let c = Cow::<[i32]>::Owned(vec![0]);
    take_ptr(c.as_ptr());
    let c = Cow::<[i32]>::Borrowed(&[1]);
    take_ptr(c.as_ptr());
}

Edit: I see that

     take_ptr(vec![2])

also does not have a lint and exposes the same problem

[mulimoen]

Duplicate of #2637 and #5965