`needless_borrow` and `explicit_auto_deref` false positive with unions

[Arc-blroth]

Summary

Clippy suggests removing explicit &mut and * derefs that are required by RFC 2514 when working with union fields.

Lint Name

needless_borrow and explicit_auto_deref

Reproducer

I tried this code:

use std::mem::ManuallyDrop;

union Coral {
    crab: ManuallyDrop<Vec<i32>>,
}

union Ocean {
    coral: ManuallyDrop<Coral>,
}

fn main() {
    let mut ocean = Ocean {
        coral: ManuallyDrop::new(Coral {
            crab: ManuallyDrop::new(vec![1, 2, 3]),
        }),
    };

    unsafe {
        // this expression borrows a value the compiler would automatically borrow
        ManuallyDrop::drop(&mut (&mut ocean.coral).crab);
        
        // deref which would be done by auto-deref
        (*ocean.coral).crab = ManuallyDrop::new(vec![4, 5, 6]);
        ManuallyDrop::drop(&mut (*ocean.coral).crab);
        
        ManuallyDrop::drop(&mut ocean.coral);
    }
}

I saw this happen:

warning: this expression borrows a value the compiler would automatically borrow
  --> src/main.rs:20:33
   |
20 |         ManuallyDrop::drop(&mut (&mut ocean.coral).crab);
   |                                 ^^^^^^^^^^^^^^^^^^ help: change this to: `ocean.coral`
   |
   = note: `#[warn(clippy::needless_borrow)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow

warning: deref which would be done by auto-deref
  --> src/main.rs:23:9
   |
23 |         (*ocean.coral).crab = ManuallyDrop::new(vec![4, 5, 6]);
   |         ^^^^^^^^^^^^^^ help: try this: `ocean.coral`
   |
   = note: `#[warn(clippy::explicit_auto_deref)]` on by default
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#explicit_auto_deref

warning: deref which would be done by auto-deref
  --> src/main.rs:24:33
   |
24 |         ManuallyDrop::drop(&mut (*ocean.coral).crab);
   |                                 ^^^^^^^^^^^^^^ help: try this: `ocean.coral`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#explicit_auto_deref

I expected to see this happen:

No warnings, since both derefs are not automatically done by the compiler.

Version

rustc 1.65.0-nightly (86c6ebee8 2022-08-16)
binary: rustc
commit-hash: 86c6ebee8fa0a5ad1e18e375113b06bd2849b634
commit-date: 2022-08-16
host: x86_64-pc-windows-msvc
release: 1.65.0-nightly
LLVM version: 15.0.0

Additional Labels

No response