# `react-hooks-js/immutability`

Validates against mutating props, state, and other values that [are immutable](https://react.dev/reference/rules/components-and-hooks-must-be-pure#props-and-state-are-immutable)

- **Status:** Active
- **Category:** React Compiler
- **Assessment:** Evidence-required risk
- **Required evidence:** source code
- **Default severity:** error
- **Scope:** All supported frameworks
- **Active when:** eslint-plugin-react-hooks v6+ installed AND React Compiler detected in project
- **Priority:** 73 (P1)
- **Source:** eslint-plugin-react-hooks
- **Rule set:** oxlint-plugin-react-doctor 0.9.3 (prompt schema 2)
- **Documentation:** [Official documentation](https://react.dev/reference/eslint-plugin-react-hooks/lints/immutability)

## Validation prompt

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

Fires on writes to values the compiler proves are immutable: props, useState values, useReducer state: via property assignment (state.x = v), in-place array methods (push, pop, splice, sort, reverse), or Object.assign(state, ...).

Suppress when: the value is an Immer produce() draft (draft.x = v is legal inside the producer) or some other proxy that intentionally exposes mutable semantics.

## 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, explicit repository policy, relevant exceptions, and required rendered or runtime evidence before deciding the occurrence. This page’s Assessment and Required evidence fields define the review contract.

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

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 or expiry condition. It is not a pass or false positive.

## Fix prompt

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

Always create a new container: setItems([...items, newItem]) or setUser({ ...user, name }): spread at every nested level you change. For deep updates prefer useReducer with explicit immutable cases, or wrap producer code in Immer's produce(). React relies on reference identity (Object.is) to detect changes, so mutating the same array/object silently skips re-renders. See https://react.dev/reference/eslint-plugin-react-hooks/lints/immutability

## Repository-wide copy prompt

Use this only for a repository-wide pass after validating each occurrence. For one occurrence, use the occurrence-level guidance above.

````text
Fix every confirmed `react-hooks-js/immutability` diagnostic in the current repository.

Required change:
- Always create a new container: setItems([...items, newItem]) or setUser({ ...user, name }): spread at every nested level you change. For deep updates prefer useReducer with explicit immutable cases, or wrap producer code in Immer's produce(). React relies on reference identity (Object.is) to detect changes, so mutating the same array/object silently skips re-renders. See https://react.dev/reference/eslint-plugin-react-hooks/lints/immutability

Validation before editing:
Fires on writes to values the compiler proves are immutable: props, useState values, useReducer state: via property assignment (state.x = v), in-place array methods (push, pop, splice, sort, reverse), or Object.assign(state, ...).

Suppress when: the value is an Immer produce() draft (draft.x = v is legal inside the producer) or some other proxy that intentionally exposes mutable semantics.

Constraints:
- Confirm every occurrence independently.
- Make the smallest change that addresses the root cause.
- Preserve unrelated behavior, interfaces, content, and semantics.
- Reuse existing project conventions and components.
- Do not suppress the rule merely to clear the report.

Assessment:
- Record detector evidence, applicability, missing evidence, and one outcome: Confirmed failure, Rejected, Needs evidence, Unavailable, Waived with evidence, or Observation.

Verification:
- Run focused tests and every repository-mandated check.
- Run React Doctor and confirm the diagnostic no longer appears from changed code.
- Run an unfiltered scan of the affected scope before claiming no cross-category regression.
- Report checks that were not run instead of claiming they passed.
````