Suggest .cast/.cast_const/.cast_mut in transmute_ptr_as_ptr

[Alexendoo]

Essentially pre-applies ptr_as_ptr - #6372 (comment)

changelog: none

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[y21]

I think this could end up as a wrong suggestion for lifetime transmutes (*mut Lt<'a> to *const Lt<'static>). Maybe we can add a check if the from- or to type has TypeFlags::RE_ERASED?

[Alexendoo]

Interesting, is there a good example? I assume this would also effect ptr_as_ptr

[y21]

Can't think of a good (practical) example, but I was thinking of something like:

struct Lt<'a>(&'a ());

unsafe fn f(v: *mut Lt<'_>) -> *const Lt<'static> {
  std::mem::transmute(v)
}

This looks like it has .cast_const() for the suggestion, but that doesn't change the lifetime

Basically just this test case but with raw pointers and with differing mutability (so it doesn't go into the first if for pointer::cast):

rust-clippy/tests/ui/transmute_ptr_to_ptr.fixed

Line 10 in afe811a

unsafe fn transmute_lifetime_to_static<'a, T>(t: &'a T) -> &'static T {

[Alexendoo]

Thanks, unrealistic is fine I just can never remember which lifetimes are erased or early/late or any of that stuff 😅

Fixed it for ptr_cast_constness too

[y21]

Looks good to me now! @bors r+

[bors]

📌 Commit 7010d3c has been approved by y21

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7010d3c with merge e91d82e...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: y21
Pushing e91d82e to master...