luma-web-review-react-state-tagged-union

Look for coexisting boolean flags like isLoading or isSubmitting alongside nullable data or error states, which allow impossible combinations such as loading with data present. This review enumerates components with two or more useState hooks and analyzes whether their state transitions are atomic.

Use a tagged union when multiple states change together, such as status plus associated data, so invalid combinations become unrepresentable at the type level. A discriminated union with a status field replaces separate isLoading, data, and error states.

Use useActionState for form submissions and Server Action calls where you currently manage loading, error, and success manually. Use useReducer when state transitions number three or more and each transition changes multiple fields, but only if useActionState does not already cover the case.

Key signals include three or more boolean flags in one component, setters always called together in pairs, and status strings stored separately from their associated data. These patterns mean most of the 2^n state combinations are invalid.

Findings are rated high when an actual code path can reach an invalid state, medium when the type allows invalid states but current code avoids them, and low for minor improvements. Each finding includes file and line, the component name, and a concrete type definition suggestion.