Do not warn when deriving Copy for raw pointers

[aochagavia]

Fixes #21272 and #21296

r? @cmr

[aochagavia]

@cmr Is there a way to test the lack of a warning?

[emberian]

@aochagavia you can use #[forbid(raw_pointer_derive)] in a run-pass test, and if the lint triggers the test will fail.

[aochagavia]

@cmr Thanks! I have added a test.

[emberian]

r? @huonw (You have the strongest opinions about this lint, I believe)

[aochagavia]

Any news on this?

[huonw]

Sorry, @aochagavia, lost track of this. I think it's good, just a small implementation nit.

[huonw]

Currently this code will mean that any trait called Copy isn't warned about, while the compiler actually has enough info to do it "perfectly", i.e. only avoid warning for the special Copy trait.

let trait_ref = ty::node_id_to_trait_ref(cx.tcx, t_ref.ref_id);
let def_id = ty::trait_ref_to_def_id(cx.tcx, trait_ref.def_id);
if Some(def_id) == cx.tcx.lang_items.copy_trait() {
    return
}

(I'm not 100% certain that will work, and I haven't compiled it.)

[huonw]

If I'm so slow again be feel to pester me.

[aochagavia]

@huonw Addressed your nit. Thanks for reviewing!

[pnkfelix]

@bors r=huonw 8b84f09

[pnkfelix]

@bors r=huonw 8b84f09 rollup

[sorccu]

Sorry to comment after closing, but should deriving Debug produce the raw_pointer_derive warning like it currently does?