update borrow_as_ptr to suggest &raw syntax

[cyrgani]

This PR updates the borrow_as_ptr lint to no longer suggest addr_of! and addr_of_mut! and instead use the preferred &raw const and &raw mut syntax.

Not sure about two things:

1. Do I need to set or update a MSRV for the lint anywhere?
2. There is a borrow_as_ptr_no_std test as well as a borrow_as_ptr test. They used to be more relevant as the lint needed to select std or core, but that is gone now, so maybe the borrow_as_ptr_no_std should be deleted?

changelog: update borrow_as_ptr to suggest &raw syntax

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[y21]

Do I need to set or update a MSRV for the lint anywhere?

Only the suggestion needs it (we can still fall back to the slightly older addr_of! and lint if the MSRV is lower than 1.82). You can add an entry to the msrvs macro

rust-clippy/clippy_config/src/msrvs.rs

Line 22 in 786fbd6

1,82,0 { IS_NONE_OR, REPEAT_N }

and pass the Msrv instance to the check function and check with msrv.meets(&msrvs::RAW_REF_OP)

[y21]

Actually now looking more into it, I don't think this would ever do anything if gated behind an MSRV, because the lint borrow_as_ptr never runs for MSRV >= 1.76 as ref_as_ptr takes precedence in that case and suggests ptr::from_ref(&x)

[cyrgani]

You're right that it doesn't lint on current versions anymore, however, I fail to understand why this version restriction was added. For example, it should warn in this example and suggest &raw or addr_of_mut!, but doesn't (and ref_as_ptr doesn't warn either and shouldn't, since the idea of &raw is to avoid any intermediate references):

#![warn(clippy::pedantic)]
fn main() {
    let mut x = 2;
    let ptr1 = &mut x as *mut i32;
    let ptr2 = &mut x as *mut i32;
    //let ptr1 = &raw mut x;
    //let ptr2 = &raw mut x;
    unsafe {
        assert_eq!(*ptr1, *ptr2);
    }
}

[Jarcho]

That's nice and broken. borrow_as_ptr should take priority as it's a more specific lint.

@cyrgani can you make this two commits with the first flipping the order of borrow_as_ptr and ref_as_ptr. Make sure to have the commit message note that borrow_as_ptr is a more specific lint.

Like @y21 mentioned you'll need the MSRV check for the suggestion.

[Jarcho]

Note when flipping the order of the lints ref_as_ptr should only be run if no diagnostic was issued for borrow_as_ptr. You'll need to explicitly check if borrow_as_ptr is allowed via clippy_utils::is_lint_allowed and return whether span_lint was actually called.

[Jarcho]

You have the right idea here, but borrow_as_pointer should be checked first.

[cyrgani]

You're right, I've swapped the checks.

[Jarcho]

Just a couple of small things remaining and this is good.

[Jarcho]

This can be moved down to where it's actually needed.

[Jarcho]

Thank you.