dbt-labs/dbt-core · error

expected `union` sequence inside exclude

Error message

expected `union` sequence inside exclude

What it means

Test-only assertion in test_serialize_atom_with_nested_exclude: the serialized selector atom's `exclude` entry must contain a `union` sequence as its single element. Fires only if selector YAML serialization flattens or drops the nested union inside exclude.

Solutions

1. Fix selector_atom_to_yaml to nest the union inside the exclude list
2. Re-run the selector serialization tests
3. Treat failure as a selector YAML shape regression

When it happens

Trigger: Thrown at crates/dbt-parser/src/resolve/resolve_selectors.rs:606 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/cec7bdc492b16944. Report an issue: GitHub.

Appendix: source

Thrown at crates/dbt-parser/src/resolve/resolve_selectors.rs:606

            ]))),
        ));

        let yaml = select_expression_to_yaml(&expr);

        assert_eq!(yaml.get("method").and_then(|v| v.as_str()), Some("fqn"));
        assert_eq!(yaml.get("value").and_then(|v| v.as_str()), Some("*"));

        // `exclude` must be a single-element list wrapping the union.
        let exclude = yaml
            .get("exclude")
            .and_then(|v| v.as_sequence())
            .expect("expected `exclude` sequence in serialized atom");
        assert_eq!(exclude.len(), 1);

        let union = exclude[0]
            .get("union")
            .and_then(|v| v.as_sequence())
            .expect("expected `union` sequence inside exclude");
        let mut tags: Vec<String> = union
            .iter()
            .map(|item| {
                assert_eq!(item.get("method").and_then(|v| v.as_str()), Some("tag"));
                item.get("value")
                    .and_then(|v| v.as_str())
                    .unwrap()
                    .to_string()
            })
            .collect();
        tags.sort();
        assert_eq!(tags, vec!["feed_service_now", "usage"]);
    }

    /// An atom without a nested exclude must not emit an `exclude` key (no
    /// spurious empty `exclude: []`).
    #[test]
    fn test_serialize_atom_without_exclude() {

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