Compiler hangs during execution

I tried this code:

trait Trait {}

struct W<T>(T);

impl<T, U> Trait for W<(<&Self as IntoIterator>, W<U>)>
where
    W<T>: Trait,
    W<U>: Trait,
{
}

fn impls<T: Trait>() {}

fn main() {
    impls::<W<_>>();
}

I expected to see this happen:

The compilation process should complete successfully, and any errors in the code should be reported with diagnostic messages.

Instead, this happened:

The compiler hangs indefinitely and appears to never terminate.

Meta

rustc --version --verbose:

rustc 1.85.1 (4eb161250 2025-03-15)
binary: rustc
commit-hash: 4eb161250e340c8f48f66e2b929ef4a5bed7c181
commit-date: 2025-03-15
host: x86_64-pc-windows-msvc
release: 1.85.1
LLVM version: 19.1.7

error: expected `::`, found `,`
 --> .\temp.rs:7:48
  |
7 | impl<T, U> Trait for W<(<&Self as IntoIterator>, W<U>)>
  |                                                ^ expected `::`

error: expected `::`, found `,`
 --> .\temp.rs:7:48
  |
7 | impl<T, U> Trait for W<(<&Self as IntoIterator>, W<U>)>
  |                                                ^ expected `::`
  |
help: expressions must be enclosed in braces to be used as const generic arguments
  |
7 | impl<T, U> Trait for W<{ (<&Self as IntoIterator>, W<U>) }>
  |                        +                                 +

error[E0747]: constant provided when a type was expected
 --> .\temp.rs:7:24
  |
7 | impl<T, U> Trait for W<(<&Self as IntoIterator>, W<U>)>
  |                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Start by compiling the minimal Rust reproducer with rustc 1.85.1 and confirm that compilation hangs instead of terminating. Investigate the compiler behavior around this input and verify that the process completes while reporting diagnostics for the invalid code.