Marker traits cause inference error when used with associated types and lifetimes

[meltah]

I tried this code:

#![feature(marker_trait_attr)]

#[marker] trait Trait<U> {}

impl<T, U> Trait<U> for T {}
impl<T, U> Trait<U> for T {}

fn check<T, U>(_: T, _: U) where T: Trait<U> {}

trait Foo { type Assoc; }
impl Foo for () {
    type Assoc = &'static u8; // changing this to a type without a lifetime fixes the bug
}

fn infer<T: Foo>(_: T) -> T::Assoc { loop {} }

fn f() {
    check((), infer(()));
}

This should compile normally, as it does if &'static u8 is replaced with, say, u8, but instead I get:

error[E0283]: type annotations needed: cannot satisfy `(): Trait<&u8>`
  --> src/lib.rs:18:5
   |
18 |     check((), infer(()));
   |     ^^^^^^^^^^^^^^^^^^^^
   |
note: multiple `impl`s satisfying `(): Trait<&u8>` found
  --> src/lib.rs:5:1
   |
5  | impl<T, U> Trait<U> for T {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
6  | impl<T, U> Trait<U> for T {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `check`
  --> src/lib.rs:8:37
   |
8  | fn check<T, U>(_: T, _: U) where T: Trait<U> {}
   |                                     ^^^^^^^^ required by this bound in `check`

Meta

rustc --version --verbose:

rustc 1.85.0-nightly (d49be02cf 2024-12-02)
binary: rustc
commit-hash: d49be02cf6d2e2a01264fcdef1e20c826710c0f5
commit-date: 2024-12-02
host: x86_64-pc-windows-msvc
release: 1.85.0-nightly
LLVM version: 19.1.4

[meltah]

Minimized even further:

#![feature(marker_trait_attr)]

#[marker] trait Trait<U> {}

impl<T, U> Trait<U> for T {}
impl<T, U> Trait<U> for T {}

fn check<T, U>(_: T, _: U) where T: Trait<U> {}

fn f() {
    check((), &());
}

[fmease]

Why do you have duplicate impl<T, U> Trait<U> for T {}, of course they're going to lead to ambiguity down the line (their conflict is deferred due to the marker attr). Does your code base where this reproducer is from also contain identical impls or is that just an artifact of minimization?

[meltah]

Just minimization. In the real code there is overlap but they're not identical. It's

#[marker] trait CanSafetyCast<To> {}
impl<From: Function, To: Function<Safety = Unsafe>> CanSafetyCast<To> for From {}
impl<From: Function<Safety = Safe>, To: Function> CanSafetyCast<To> for From {}

[meltah]

Okay, the generic and the inferred type aren't even required:

#![feature(marker_trait_attr)]

#[marker] trait Trait {}

impl<T> Trait for T {}
impl<T> Trait for T {}

fn check<T: Trait>() {}

fn f() {
    check::<&'static ()>();
}

[meltah]

Duplicate of #89515.