ptr_as_ptr: suggestion does not take `std::ptr::null` into account

[KisaragiEffective]

Summary

ptr_as_ptr suggests expr.cast::<Ty>() even if expr is std::ptr::null() or std::ptr::null_mut().

Reproducer

I tried this code:

#![deny(clippy::ptr_as_ptr)]
fn x() {
    let a = std::ptr::null() as *const u8;
}

I expected to see this happen:

error: `as` casting between raw pointers without changing its mutability
 --> src/lib.rs:3:13
  |
3 |     let a = std::ptr::null() as *const u8;
  |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try call directly: `std::ptr::null::<u8>()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_as_ptr
note: the lint level is defined here
 --> src/lib.rs:1:9
  |
1 | #![deny(clippy::ptr_as_ptr)]
  |         ^^^^^^^^^^^^^^^^^^

Instead, this happened:

error: `as` casting between raw pointers without changing its mutability
 --> src/lib.rs:3:13
  |
3 |     let a = std::ptr::null() as *const u8;
  |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try `pointer::cast`, a safer alternative: `std::ptr::null().cast::<u8>()`
  |
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ptr_as_ptr
note: the lint level is defined here
 --> src/lib.rs:1:9
  |
1 | #![deny(clippy::ptr_as_ptr)]
  |         ^^^^^^^^^^^^^^^^^^

Version

rustc 1.74.0 (79e9716c9 2023-11-13)
binary: rustc
commit-hash: 79e9716c980570bfd1f666e3b16ac583f0168962
commit-date: 2023-11-13
host: x86_64-unknown-linux-gnu
release: 1.74.0
LLVM version: 17.0.4

Additional Labels

@rustbot labels +I-suggestion-causes-error

[KisaragiEffective]

@rustbot claim