Error code E0320

Recursion limit reached while creating drop-check rules.

Example of erroneous code:

#![allow(unused)] fn main() { enum A<T> { B, C(T, Box<A<(T, T)>>) } fn foo<T>() { A::<T>::B; // error: overflow while adding drop-check rules for A<T> } }

The Rust compiler must be able to reason about how a type is Dropped, and by extension the types of its fields, to be able to generate the glue to properly drop a value. The code example above shows a type where this inference is impossible because it is recursive. Note that this is not the same as E0072, where a type has an infinite size; the type here has a finite size but any attempt to Drop it would recurse infinitely. For more information, read the Drop docs.

It is not possible to define a type with recursive drop-check rules. All such recursion must be removed.