Compiler hangs; doesn't detect "overflow evaluating the requirement" in case of dyn closure

[JanBeh]

Problem

I tried this code:

pub trait Trait1<T> {
    type Assoc;
}

impl<T, U> Trait1<U> for T {
    type Assoc = U;
}

pub type Alias<A, B> =
    &'static dyn FnMut(A) -> B; // hangs
    //&'static fn(A) -> B; // gives error

pub trait Trait2<T> {}

impl<T, U> Trait2<U> for T
where
    T: Trait1<Alias<T, U>>,
    <T as Trait1<Alias<T, U>>>::Assoc: Trait2<U>,
{
}

(Playground)

I expect to get some sort of error at least, but instead the compiler hangs.

If I use &'static fn(A) -> B instead of &'static dyn FnMut(A) -> B, an error will be reported instead:

error[E0275]: overflow evaluating the requirement `&'static fn(&'static fn(&'static fn(&'static ...) -> ...) -> ...) -> ...: Trait1<...>`
  --> src/main.rs:18:40
   |
18 |     <T as Trait1<Alias<T, U>>>::Assoc: Trait2<U>,
   |                                        ^^^^^^^^^
   |
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`hang`)
note: required for `&fn(&fn(&fn(&...) -> ...) -> ...) -> ...` to implement `Trait2<U>`
  --> src/main.rs:15:12
   |
15 | impl<T, U> Trait2<U> for T
   |            ^^^^^^^^^     ^
16 | where
17 |     T: Trait1<Alias<T, U>>,
   |        ------------------- unsatisfied trait bound introduced here
   = note: the full type name has been written to '/usr/home/jbe/rust-experiment/hang/target/debug/deps/hang-26babc5805012eba.long-type-4138312560499222288.txt'
   = note: 126 redundant requirements hidden
   = note: required for `<T as Trait1<&'static fn(T) -> U>>::Assoc` to implement `Trait2<U>`

For more information about this error, try `rustc --explain E0275`.

Meta

rustc --version --verbose:

rustc 1.72.0-nightly (f20afcc45 2023-07-04)
binary: rustc
commit-hash: f20afcc455bbcc5c0f7679450fb35fd0c9668880
commit-date: 2023-07-04
host: x86_64-unknown-freebsd
release: 1.72.0-nightly
LLVM version: 16.0.5

Possibly related

• Indefinitely hangs on hidden "overflow evaluating the requirement" errors when the complexity is too high. #92822
• Trait resolver hangs when evaluating cyclic requirement with lifetimes #96340
• Hang with weird recursive associated type #104230

[teofr]

Been playing around a little bit with this, and it seems that it's not a cycle detection problem or anything like that, rather a slower grow rate of the stack. Decreasing the recursion limit fixes the issue, still worth a look.
Also simplified the example a bit:

// #![recursion_limit = "8"]

pub trait Trait2<T> {}

impl<T, U> Trait2<U> for T
where
    &'static dyn FnOnce(T) -> U: Trait2<U>,
    // &'static fn(T) -> U: Trait2<U>,
{
}

Playground