Cycle detected while trying to transmute future

I tried this code:

use std::mem::MaybeUninit;

fn main() {
    let fut = async {};
    let cast: [MaybeUninit<u8>; 1] = unsafe { std::mem::transmute(fut) };
}

I was playing around and expected this to succeed, instead, it resulted in this:

error[E0391]: cycle detected when type-checking `main`
 --> src/main.rs:3:1
  |
3 | fn main() {
  | ^^^^^^^^^
  |
  = note: ...which requires computing layout of `{async block@src/main.rs:4:15: 4:23}`...
note: ...which requires optimizing MIR for `main::{closure#0}`...
 --> src/main.rs:4:15
  |
4 |     let fut = async {};
  |               ^^^^^^^^
note: ...which requires elaborating drops for `main::{closure#0}`...
 --> src/main.rs:4:15
  |
4 |     let fut = async {};
  |               ^^^^^^^^
note: ...which requires coroutine witness types for `main::{closure#0}`...
 --> src/main.rs:4:15
  |
4 |     let fut = async {};
  |               ^^^^^^^^
note: ...which requires promoting constants in MIR for `main::{closure#0}`...
 --> src/main.rs:4:15
  |
4 |     let fut = async {};
  |               ^^^^^^^^
note: ...which requires checking if `main::{closure#0}` contains FFI-unwind calls...
 --> src/main.rs:4:15
  |
4 |     let fut = async {};
  |               ^^^^^^^^
note: ...which requires building MIR for `main::{closure#0}`...
 --> src/main.rs:4:15
  |
4 |     let fut = async {};
  |               ^^^^^^^^
note: ...which requires match-checking `main::{closure#0}`...
 --> src/main.rs:4:15
  |
4 |     let fut = async {};
  |               ^^^^^^^^
note: ...which requires type-checking `main::{closure#0}`...
 --> src/main.rs:4:15
  |
4 |     let fut = async {};
  |               ^^^^^^^^
  = note: ...which again requires type-checking `main`, completing the cycle
  = note: cycle used when running analysis passes on this crate
  = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information

Meta

rustc --version --verbose:

rustc 1.80.0-nightly (87293c958 2024-05-08)
binary: rustc
commit-hash: 87293c9585a7fb2cc83ca9949ae79661d5d3c31a
commit-date: 2024-05-08
host: x86_64-unknown-linux-gnu
release: 1.80.0-nightly
LLVM version: 18.1.4

Start by reproducing the example in src/main.rs with the reported rustc 1.80.0-nightly toolchain. Trace the cycle through async-block type checking, layout computation, MIR optimization, drop elaboration, coroutine witness types, and the other queries named in the diagnostic. Done means the reproduction no longer produces the reported cycle or has a clear, appropriate compiler diagnostic.