# `react-doctor/zustand-no-mutating-state`

Zustand state mutated in place

- **Category:** Bugs
- **Severity:** error
- **Source:** oxlint-plugin-react-doctor
- **Framework:** global
- **Enabled when:** react, zustand, zustand:1

## Validate the diagnostic

Confirm the reported code matches this rule before you edit it.

Confirm the reported code matches `react-doctor/zustand-no-mutating-state`. Compare it with the Before example and verify the same API, framework, and execution context. Treat it as a false positive only when one of those conditions differs.

## Compare the code

The corrected pattern shows a focused way to address the diagnostic.

### Reported pattern

```ts
import { create } from "zustand";

interface Todo {
  id: string;
}

interface TodoStore {
  todos: Todo[];
  addTodo: (todo: Todo) => void;
}

const useTodoStore = create<TodoStore>((set) => ({
  todos: [],
  addTodo: (todo) =>
    set((state) => {
      state.todos.push(todo);
      return { todos: state.todos };
    }),
}));
```

### Corrected pattern

```ts
import { create } from "zustand";

interface Todo {
  id: string;
}

interface TodoStore {
  todos: Todo[];
  addTodo: (todo: Todo) => void;
}

const useTodoStore = create<TodoStore>((set) => ({
  todos: [],
  addTodo: (todo) =>
    set((state) => ({
      todos: [...state.todos, todo],
    })),
}));
```

## How to fix

Use the corrected pattern as a reference. Preserve behavior that the rule does not require you to change.

### Copyable fix prompt

Copy this self-contained prompt into your coding agent after you confirm the diagnostic.

````text
Fix every confirmed `react-doctor/zustand-no-mutating-state` diagnostic in the current repository.

Required change:
- Create a new object, array, Map, or Set before passing the updated value to Zustand.

Reference transformation:

Before:
```ts
import { create } from "zustand";

interface Todo {
  id: string;
}

interface TodoStore {
  todos: Todo[];
  addTodo: (todo: Todo) => void;
}

const useTodoStore = create<TodoStore>((set) => ({
  todos: [],
  addTodo: (todo) =>
    set((state) => {
      state.todos.push(todo);
      return { todos: state.todos };
    }),
}));
```

After:
```ts
import { create } from "zustand";

interface Todo {
  id: string;
}

interface TodoStore {
  todos: Todo[];
  addTodo: (todo: Todo) => void;
}

const useTodoStore = create<TodoStore>((set) => ({
  todos: [],
  addTodo: (todo) =>
    set((state) => ({
      todos: [...state.todos, todo],
    })),
}));
```

Constraints:
- Confirm the reported code matches the Before pattern.
- Make the smallest change that fixes the root cause.
- Preserve behavior and interfaces unrelated to this diagnostic.
- Reuse existing project components, utilities, and conventions.
- Do not introduce render-phase side effects, render-phase state updates, or Hooks rule violations.
- Adapt identifiers and framework details instead of copying blindly.
- Do not disable the rule or suppress matching code.
- Confirm this rule is enabled for the project: `react, zustand, zustand:1`.

Verification:
- Run focused tests for the changed behavior.
- Run React Doctor and confirm this diagnostic no longer appears.
- Report the files changed and any checks you could not run.
````