Confusing error message with unaligned access to `packed(n > 1)` fields

[mkeeter]

Code

#[repr(C, packed(4))]
pub struct Data {
    oxide_magic: u32,
    header_version: u32,
    monotonic_counter: u64,
    slot_select: u32,
}

fn main() {
    let d = Data {
        oxide_magic: 1,
        header_version: 1,
        monotonic_counter: 4,
        slot_select: 15,
    };
    println!("{}", d.monotonic_counter);
}

Current output

error[E0793]: reference to packed field is unaligned
  --> src/main.rs:16:20
   |
16 |     println!("{}", d.monotonic_counter);
   |                    ^^^^^^^^^^^^^^^^^^^
   |
   = note: packed structs are only aligned by one byte, and many modern architectures penalize unaligned field accesses
   = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
   = note: this error originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0793`.
error: could not compile `playground` (bin "playground") due to 1 previous er

Desired output

Something along the lines of

   = note: this struct is aligned to 4 bytes, but the variable requires 8-byte alignment
   = note: many modern architectures penalize unaligned field accesses
   = ...etc

Rationale and extra context

It's confusing to see packed structs are only aligned by one byte when I have specified packed(4)

Rust Version

rustc 1.90.0 (1159e78c4 2025-09-14)
binary: rustc
commit-hash: 1159e78c4747b02ef996e55082b704c09b970588
commit-date: 2025-09-14
host: aarch64-apple-darwin
release: 1.90.0
LLVM version: 20.1.8

[21aslade]

I'd like to work on this! (My first issue, seems simple enough.)

@rustbot claim