error[E0391]: cycle detected when computing when `List` needs drop --> src/main.rs:1:1 | 1 | enum List { | ^^^^^^^^^ | = note: ...which immediately requires computing when `List` needs drop again = note: cycle used when computing whether `List` needs drop = note: see https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information