rust-analyzer doesn't like zerocopy::KnownLayout on DSTs

[allisonkarlitskaya]

rust-analyzer version: rust-analyzer 1.83.0 via rust-analyzer-1.83.0-1.fc41.x86_64
rustc version: rustc 1.83.0 (90b35a623 2024-11-26) (Fedora 1.83.0-1.fc41) via rust-1.83.0-1.fc41.x86_64
editor or extension: nvim from Fedora 41: neovim-0.10.2-1.fc41.x86_64
relevant settings:

LSP configs active in this buffer (bufnr: 1) ~
- Language client log: ~/.local/state/nvim/lsp.log
- Detected filetype: `rust`
- 1 client(s) attached to this buffer
- Client: `rust_analyzer` (id: 1, bufnr: [1])
  root directory:    ~/src/reproducer/
  filetypes:         rust
  cmd:               /usr/local/bin/rust-analyzer
  version:           `rust-analyzer 1.85.0-nightly (d4025ee 2024-12-12)`
  executable:        true
  autostart:         true

code snippet to reproduce:

// add your code here
use zerocopy::KnownLayout;

#[derive(KnownLayout)]
#[repr(C)]
struct Flexible {
    header: u32,
    body: [u8],
}

This gets you

1. casting `*mut _` as `*mut __ZerocopyKnownLayoutMaybeUninit` is invalid: vtable kinds may not match [E0606]
2. casting `*mut __ZerocopyKnownLayoutMaybeUninit` as `*mut _` is invalid: vtable kinds may not match [E0606]

but with cargo build it's fine.

This is caused by Flexible being a DST (dynamically sized type). Dropping the variable-sized body: [u8] field makes the problem go away.

I also tried with nightly (rust-analyzer 1.85.0-nightly (d4025ee 2024-12-12)) without improvement.