TAIT: requires bounds on type alias when shouldn't

I tried this code: playground:

#![feature(type_alias_impl_trait)]

type Foo<'a, C> = impl Sized;

#[define_opaque(Foo)]
fn foo<'a, C: PartialEq>(c: &'a C) -> Foo<'a, C> {
    bar(c)
}

fn bar<'a, C: PartialEq>(_: &'a C) -> impl Sized {
    0i32
}

fn main() {}

I expected to see this happen: foo has PartialEq bound, so could should compile.

Instead, this happened: it asks to put PartialEq bound in Foo itself. It implies all problems that arise after prematurely putting bounds on a struct.

❯ cargo check
    Checking play v0.1.0 (/home/ddystopia/code/play)
error[E0277]: can't compare `C` with `C`
  --> src/main.rs:7:5
   |
 7 |     bar(c)
   |     ^^^^^^ no implementation for `C == C`
   |
note: required by a bound in `bar`
  --> src/main.rs:10:15
   |
10 | fn bar<'a, C: PartialEq>(_: &'a C) -> impl Sized {
   |               ^^^^^^^^^ required by this bound in `bar`
help: consider restricting type parameter `C` with trait `PartialEq`
   |
 3 | type Foo<'a, C: std::cmp::PartialEq> = impl Sized;
   |               +++++++++++++++++++++

For more information about this error, try `rustc --explain E0277`.
error: could not compile `play` (bin "play") due to 1 previous error

Meta

rustc --version --verbose:

rustc 1.93.0-nightly (adaa83897 2025-10-27)
binary: rustc
commit-hash: adaa838976ff99a4f0661136322f64cb466b58a0
commit-date: 2025-10-27
host: x86_64-unknown-linux-gnu
release: 1.93.0-nightly
LLVM version: 21.1.3

Start by reproducing the supplied type_alias_impl_trait example with the nightly compiler using cargo check. Investigate how the compiler handles the #[define_opaque] function and bounds on the type alias versus its function parameters. Done means the example compiles without requiring the PartialEq bound on Foo, with regression coverage for this behavior.