dbt-labs/dbt-core · error

Downcast failed

Error message

Downcast failed

What it means

Test helper assertion in assert_dyn_eq: after downcasting the boxed dyn ComponentConfig back to its concrete type T via as_any().downcast_ref(), the downcast returned None. This guard verifies the Any plumbing of component configs; it fails only if T does not match the boxed component's concrete type.

Solutions

1. Ensure assert_dyn_eq is called with the same concrete type that was boxed
2. Check that SimpleComponentConfigImpl implements as_any returning the correct Self type
3. Treat failure as a test-helper misuse, not a runtime error

When it happens

Trigger: Thrown at crates/dbt-adapter/src/relation/config_v2.rs:771 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of dbt-labs/dbt-core@0267ce9170 (2026-09-07). Data as JSON: /api/errors/25f3bdb936484327. Report an issue: GitHub.

Appendix: source

Thrown at crates/dbt-adapter/src/relation/config_v2.rs:771

        fn eq(&self, other: &Self) -> bool {
            self.value == other.value
        }
    }

    impl<T: Eq + fmt::Debug + Send + Sync + Any + Clone> Eq for SimpleComponentConfigImpl<T> {}

    fn custom_diff(desired_state: &u8, current_state: &u8) -> Option<u8> {
        let diff = desired_state - current_state;
        if diff != 0 { Some(diff) } else { None }
    }

    fn assert_dyn_eq<T: Clone + Eq + fmt::Debug + 'static>(a: T, b: Box<dyn ComponentConfig>) {
        assert_eq!(
            a,
            b.as_ref()
                .as_any()
                .downcast_ref::<T>()
                .expect("Downcast failed")
                .clone()
        )
    }

    fn assert_component_config_change_eq<T: fmt::Debug + PartialEq + 'static>(
        a: &ComponentConfigChange,
        b: &ComponentConfigChange,
    ) {
        assert_eq!(std::mem::discriminant(a), std::mem::discriminant(b));
        if let (ComponentConfigChange::Some(a_diff), ComponentConfigChange::Some(b_diff)) = (a, b) {
            assert_eq!(
                a_diff.as_any().downcast_ref::<T>(),
                b_diff.as_any().downcast_ref::<T>()
            );
        }
    }

    fn return_true(_: &IndexMap<&'static str, ComponentConfigChange>) -> bool {

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