"expected opaque type, found ..." when trait impl with type_alias_impl_trait

I tried this code:

type U32Iter = impl Iterator<Item = u32>;

struct Foo {
    iter: U32Iter,
}

impl From<u32> for Foo {
    fn from(value: u32) -> Self {
        Self {
            iter: std::iter::once(value),
        }
    }
}

I expected to see this happen: Compiles

Instead, this happened:

12 |             iter: std::iter::once(value),
   |                   ^^^^^^^^^^^^^^^^^^^^^^ expected opaque type, found `Once<u32>`

Meta

rustc --version --verbose:

rustc 1.84.0 (9fc6b4312 2025-01-07)
binary: rustc
commit-hash: 9fc6b43126469e3858e2fe86cafb4f0fd5068869
commit-date: 2025-01-07
host: x86_64-unknown-linux-gnu
release: 1.84.0
LLVM version: 19.1.5

   Compiling smth v0.1.0 (/tmp/smth)
error[E0308]: mismatched types
  --> src/main.rs:12:19
   |
3  | type U32Iter = impl Iterator<Item = u32>;
   |                ------------------------- the expected opaque type
...
12 |             iter: std::iter::once(value),
   |                   ^^^^^^^^^^^^^^^^^^^^^^ expected opaque type, found `Once<u32>`
   |
   = note: expected opaque type `U32Iter`
                   found struct `std::iter::Once<u32>`
note: this item must have the opaque type in its signature in order to be able to register hidden types
  --> src/main.rs:10:8
   |
10 |     fn from(value: u32) -> Self {
   |        ^^^^

For more information about this error, try `rustc --explain E0308`.
error: could not compile `smth` (bin "smth") due to 1 previous error

Start by reproducing the minimal type_alias_impl_trait example with rustc 1.84.0 and investigate how the compiler handles the opaque type in the From trait implementation. Done means the example compiles as expected and the behavior is covered by a regression test.