redundant_pattern_matching: no `is_none()` for raw pointer

[matthiaskrgr]

Summary

.

Lint Name

redundant_pattern_matching

Reproducer

I tried this code:

use std::mem;

// If this is `None`, the metadata becomes padding.
type T = Option<&'static str>;

fn main() {
    unsafe {
        let mut p: mem::MaybeUninit<T> = mem::MaybeUninit::zeroed();
        // The copy when `T` is returned from `transmute` should destroy padding
        // (even when we use `write_unaligned`, which under the hood uses an untyped copy).
        p.as_mut_ptr().write_unaligned(mem::transmute((0usize, 0usize)));
        // Null epresents `None`.
        assert!(matches!(*p.as_ptr(), None));

        // The second part, with the length, becomes padding.
        let c = &p as *const _ as *const u8;
        // Read a padding byte.
        let _val = *c.add(mem::size_of::<*const u8>());
        //~^ERROR: uninitialized
    }
}

I saw this happen:

warning: redundant pattern matching, consider using `is_none()`
  --> src/main.rs:13:17
   |
13 |         assert!(matches!(*p.as_ptr(), None));
   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: try: `*p.as_ptr().is_none()`
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#redundant_pattern_matching
   = note: `#[warn(clippy::redundant_pattern_matching)]` on by default

This does not compile:

error[E0599]: no method named `is_none` found for raw pointer `*const std::option::Option<&str>` in the current scope
   --> src/main.rs:13:29
    |
13  |         assert!(*p.as_ptr().is_none());
    |                             ^^^^^^^ method not found in `*const Option<&str>`
    |
note: the method `is_none` exists on the type `&std::option::Option<&str>`
   --> /home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/option.rs:651:5
    |
651 |     pub const fn is_none(&self) -> bool {
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: you might want to use the unsafe method `<*const T>::as_ref` to get an optional reference to the value behind the pointer
    = note: read the documentation for `<*const T>::as_ref` and ensure you satisfy its safety preconditions before calling it to avoid undefined behavior: https://doc.rust-lang.org/std/primitive.pointer.html#method.as_ref

Version

rustc 1.85.0-nightly (8742e0556 2024-12-28)
binary: rustc
commit-hash: 8742e0556dee3c64f7144de2fb2e88936418865a
commit-date: 2024-12-28
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.6

Additional Labels

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