Derive macros don't bound associated types consistently

[harudagondi]

I tried this code:

trait Bar { type Qux; }

#[derive(Clone)]
struct Foo<T>(T::Qux) where T: Bar;

#[derive(Clone)]
struct Zoo<T>(<T as Bar>::Qux) where T: Bar;

I expected to see this happen: No error.

Instead, this happened:

Error on Long only:

error[E0277]: the trait bound `<T as Bar>::Qux: Clone` is not satisfied
 --> src/lib.rs:8:16
  |
7 | #[derive(Clone)]
  |          ----- in this derive macro expansion
8 | struct Long<T>(<T as Bar>::Qux) where T: Bar;
  |                ^^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `<T as Bar>::Qux`
  |
  = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)

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

Macro output:

#![feature(prelude_import)]
#[prelude_import]
use std::prelude::rust_2024::*;
#[macro_use]
extern crate std;
trait Bar {
    type Qux;
}

struct Short<T>(T::Qux) where T: Bar;
#[automatically_derived]
impl<T: ::core::clone::Clone> ::core::clone::Clone for Short<T> where T: Bar,
    T::Qux: ::core::clone::Clone {
    #[inline]
    fn clone(&self) -> Short<T> {
        Short(::core::clone::Clone::clone(&self.0))
    }
}

struct Long<T>(<T as Bar>::Qux) where T: Bar;
#[automatically_derived]
impl<T: ::core::clone::Clone> ::core::clone::Clone for Long<T> where T: Bar {
    #[inline]
    fn clone(&self) -> Long<T> { Long(::core::clone::Clone::clone(&self.0)) }
}

Meta

Playground link.

Tested on both stable 1.85.1 and nightly 1.88.0-nightly (2025-03-31 0b45675).

[moxian]

See also: #122531 and #26925
@rustbot label: +A-macros +S-has-mcve +T-compiler -needs-triage +A-associated-items

[theemathas]

Duplicate of #50730

[lcnr]

Thank you for opening this issue. Closing as duplicate