Rust errors / Types and traits
Rust compiler error · checked with rustc 1.99.0
Rust error E0391: cycle detected when computing the super clauses of `FirstTrait`
What it meansA type dependency cycle has been encountered.
What rustc prints
error[E0391]: cycle detected when computing the super clauses of `FirstTrait` --> main.rs:1:20 | 1 | trait FirstTrait : SecondTrait { | ^^^^^^^^^^^ | note: ...which requires computing the super clauses of `SecondTrait`... --> main.rs:5:21 | 5 | trait SecondTrait : FirstTrait { | ^^^^^^^^^^ = note: ...which again requires computing the super clauses of `FirstTrait`, completing the cycle note: cycle used when checking that `FirstTrait` is well-formed --> main.rs:1:1 | 1 | trait FirstTrait : SecondTrait { | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ = note: for more information, see <https://rustc-dev-guide.rust-lang.org/overview.html#queries> and <https://rustc-dev-guide.rust-lang.org/query.html>
Real output of rustc 1.99.0 compiling the official example below (2021 edition). Your names and line numbers will differ; the first line is the part to match.
The compiler team's explanation
A type dependency cycle has been encountered.
Erroneous code example:
trait FirstTrait : SecondTrait {
}
trait SecondTrait : FirstTrait {
}The previous example contains a circular dependency between two traits: FirstTrait depends on SecondTrait which itself depends on FirstTrait.
See https://rustc-dev-guide.rust-lang.org/overview.html#queries and https://rustc-dev-guide.rust-lang.org/query.html for more information.
From rustc --explain E0391 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.
Related errors
- E0308mismatched types
- E0277the trait bound is not satisfied
- E0599no method named X found in the current scope
- E0433failed to resolve
- E0380auto traits cannot have associated items
- E0390cannot define inherent `impl` for primitive types
- E0393the type parameter `T` must be explicitly specified
- E0401can't use generic parameters from outer item
Up next
Often hit nextE0308: mismatched typesA related error from the same family.Read it next →Did this answer your question?