dbt-labs/dbt-core · error

array definition should become a union

Error message

array definition should become a union

What it means

Test-only assertion in test_serialize_selector_definition_array_as_union: an array-valued selector definition must serialize as a `union` sequence in the YAML output. Fires only if array definitions stop being converted to union form.

Solutions

1. Fix selector_definition_to_yaml to map Array definitions to a union
2. Add coverage for multi-element arrays if missing
3. Treat failure as a selector serialization regression

When it happens

Trigger: Thrown at crates/dbt-parser/src/resolve/resolve_selectors.rs:657 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/6c50c8d650d11761. Report an issue: GitHub.

Appendix: source

Thrown at crates/dbt-parser/src/resolve/resolve_selectors.rs:657

        assert_eq!(
            yaml.get("method").and_then(|v| v.as_str()),
            Some("config.materialized")
        );
    }

    #[test]
    fn test_serialize_selector_definition_array_as_union() {
        let definition = SelectorDefinitionValue::Array(vec![
            SelectorDefinitionValue::String("a".to_string()),
            SelectorDefinitionValue::String("b".to_string()),
        ]);
        let yaml = selector_definition_to_yaml(&definition).unwrap();

        let sequence = yaml
            .get("union")
            .and_then(|value| value.as_sequence())
            .expect("array definition should become a union");
        assert_eq!(sequence.len(), 2);
        assert_eq!(sequence[0].get("value").and_then(|v| v.as_str()), Some("a"));
        assert_eq!(sequence[1].get("value").and_then(|v| v.as_str()), Some("b"));
    }

    #[test]
    fn test_serialize_method_key_requires_one_entry() {
        let method_value = BTreeMap::from([
            ("selector".to_string(), SelectorValue::from("base").into()),
            ("fqn".to_string(), SelectorValue::from("other").into()),
        ]);
        let atom = AtomExpr::MethodKey(method_value);

        assert!(selector_atom_to_yaml(&atom).is_err());
    }

    #[test]
    fn test_manifest_selector_preserves_union_with_inline_exclude_shape() -> FsResult<()> {

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