rustdoc: hang/OOM with recursive type

[matthiaskrgr]

I tried this code from tests/ui/recursion/issue-38591-non-regular-dropck-recursion.rs

struct S<T> {
    t: T,
    s: Box<S<fn(u: T)>>,
}

fn f(x: S<u32>) {}

fn main() {
    // Force instantiation.
    f as fn(_);
}

[GuillaumeGomez]

Some extra information:

rustdoc foo.rs 

thread 'rustc' has overflowed its stack
fatal runtime error: stack overflow
Aborted (core dumped)

When building with rustc directly:

rustc foo.rs 
warning: unused variable: `x`
 --> foo.rs:6:6
  |
6 | fn f(x: S<u32>) {}
  |      ^ help: if this is intentional, prefix it with an underscore: `_x`
  |
  = note: `#[warn(unused_variables)]` on by default

error[E0320]: overflow while adding drop-check rules for S<u32>
 --> foo.rs:6:6
  |
6 | fn f(x: S<u32>) {}
  |      ^
  |
  = note: overflowed on S<fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(fn(u32)))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))>

error: aborting due to previous error; 1 warning emitted

[fmease]

Triage: No change.

[fmease]

At the time of writing the next trait solver seems to fix this. Not sure if that's coincidental/spurious or proper. Let's see.