Better errors for polymorphic recursion

Code

enum Nested<T> {
    End,
    Cons(T, Box<Nested<Vec<T>>>),
}

fn length<T>(x: Nested<T>) -> u64 {
    match x {
        Nested::End => 1,
        Nested::Cons(_, xs) => 1 + length(*xs)
    }
}

Current output

Compiling playground v0.0.1 (/playground)
error[E0320]: overflow while adding drop-check rules for `Nested<T>`
 --> src/lib.rs:6:14
  |
6 | fn length<T>(x: Nested<T>) -> u64 {
  |              ^
  |
  = note: overflowed on `Nested<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`

error[E0320]: overflow while adding drop-check rules for `Box<Nested<Vec<T>>>`
 --> src/lib.rs:9:25
  |
9 |         Nested::Cons(_, xs) => 1 + length(*xs)
  |                         ^^
  |
  = note: overflowed on `Nested<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`

error[E0320]: overflow while adding drop-check rules for `Nested<Vec<T>>`
 --> src/lib.rs:9:43
  |
9 |         Nested::Cons(_, xs) => 1 + length(*xs)
  |                                           ^^^
  |
  = note: overflowed on `Nested<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<Vec<T>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>`

For more information about this error, try `rustc --explain E0320`.
error: could not compile `playground` (lib) due to 3 previous errors

Desired output

Not sure what an ideal output would be (Is polymorphic recursion too complex/confusing a term? Presumably if someone is writing code like the above they might know what it is), but ideally something that doesn't spam ~120 Vecs at you when erroring.

Rationale and extra context

Polymorphic recursion is not valid in rust, due to both drop restrictions (what causes the error above), and monomorphization restrictions (it cannot be monomorphized). The current errors are not very explanatory as to what the core issue is.

Other cases

Rust Version

$ rustc 1.85.0-nightly (917bfa784 2024-12-26)
binary: rustc
commit-hash: 917bfa78478cbcc77406e5ea37b24c3eedefacf4
commit-date: 2024-12-26
host: x86_64-unknown-linux-gnu
release: 1.85.0-nightly
LLVM version: 19.1.6

Anything else?

No response

Start by reproducing the issue with the Nested example using the reported rustc 1.85.0-nightly version, then read the existing E0320 explanation with rustc --explain E0320. The desired result is a more explanatory diagnostic for polymorphic recursion that avoids printing the deeply repeated Vec type; the issue does not identify source files or tests.