react-doctor/no-derived-state

Disallow storing derived state in an effect.

Validation prompt

Confirm the detector match and collect the required evidence before deciding whether an edit is warranted.

Fires on a cleanup-less useEffect where a setState's arguments derive from state or props (avoidDerivedState message), OR where the setter is only ever called from this one spot and its inputs exactly match the effect's deps (avoidSingleSetter: the value is always in sync with deps).

Suppress when: the derived computation is expensive enough you want caching: but useMemo is the right tool, not useState + useEffect.

Evidence boundary

The diagnostic proves only that the detector’s modeled source pattern matched. It does not prove runtime impact, product intent, rendered failure, or that one remediation is correct.

Establish the environment, repository policy, exceptions, and required rendered or runtime evidence before deciding the occurrence.

Record one outcome:

• Confirmed failure: The required evidence establishes the violation.
• Rejected: A documented exception or false-positive predicate applies.
• Needs evidence: Named evidence can still be collected.
• Unavailable: Required evidence cannot be collected in this run.
• Waived with evidence: An authorized, scoped exception applies to an established failure.
• Observation: The review records an optional tradeoff without claiming a defect.

A waiver records its scope, authority, evidence, and review condition. It is not a pass or false positive.

Default severity is registry metadata. Use the occurrence’s JSON severity after repository configuration when ordering real findings.

Fix prompt

Apply this candidate correction only after the required evidence confirms the risk.

Delete the useState and useEffect and compute inline during render: const fullName = firstName + ' ' + lastName. For genuinely expensive transforms wrap in useMemo(() => transform(input), [input]). Mirroring derived values into state guarantees a wasted second render every time the source changes, and risks the two falling out of sync if a future code path forgets to call the setter. See https://react.dev/learn/you-might-not-need-an-effect#updating-state-based-on-props-or-state

Repository-wide copy prompt

Use this repository-wide prompt only after validating each occurrence. For one occurrence, use the guidance above.