[New] no-unstable-nested-components: Prevent creating unstable comp…

…onents inside components

README.md

@@ -132,6 +132,7 @@ Enable the rules that you would like to use.
 * [react/no-unescaped-entities](docs/rules/no-unescaped-entities.md): Detect unescaped HTML entities, which might represent malformed tags
 * [react/no-unknown-property](docs/rules/no-unknown-property.md): Prevent usage of unknown DOM property (fixable)
 * [react/no-unsafe](docs/rules/no-unsafe.md): Prevent usage of unsafe lifecycle methods
+* [react/no-unstable-nested-components](docs/rules/no-unstable-nested-components.md): Prevent creating unstable components inside components
 * [react/no-unused-prop-types](docs/rules/no-unused-prop-types.md): Prevent definitions of unused prop types
 * [react/no-unused-state](docs/rules/no-unused-state.md): Prevent definition of unused state fields
 * [react/no-will-update-set-state](docs/rules/no-will-update-set-state.md): Prevent usage of setState in componentWillUpdate

docs/rules/no-unstable-nested-components.md

@@ -0,0 +1,142 @@
+# Prevent creating unstable components inside components (react/no-unstable-nested-components)
+
+Creating components inside components without memoization leads to unstable components. The nested component and all its children are recreated during each re-render. Given stateful children of the nested component will lose their state on each re-render.
+
+React reconcilation performs element type comparison with [reference equality](https://github.com/facebook/react/blob/v16.13.1/packages/react-reconciler/src/ReactChildFiber.js#L407). The reference to the same element changes on each re-render when defining components inside the render block. This leads to complete recreation of the current node and all its children. As a result the virtual DOM has to do extra unnecessary work and [possible bugs are introduced](https://codepen.io/ariperkkio/pen/vYLodLB).
+
+## Rule Details
+
+The following patterns are considered warnings:
+
+```jsx
+function Component() {
+  function UnstableNestedComponent() {
+    return <div />;
+  }
+
+  return (
+    <div>
+      <UnstableNestedComponent />
+    </div>
+  );
+}
+```
+
+```jsx
+function SomeComponent({ footer: Footer }) {
+  return (
+    <div>
+      <Footer />
+    </div>
+  );
+}
+
+function Component() {
+  return (
+    <div>
+      <SomeComponent footer={() => <div />} />
+    </div>
+  );
+}
+```
+
+```jsx
+class Component extends React.Component {
+  render() {
+    function UnstableNestedComponent() {
+      return <div />;
+    }
+
+    return (
+      <div>
+        <UnstableNestedComponent />
+      </div>
+    );
+  }
+}
+```
+
+The following patterns are **not** considered warnings:
+
+```jsx
+function OutsideDefinedComponent(props) {
+  return <div />;
+}
+
+function Component() {
+  return (
+    <div>
+      <OutsideDefinedComponent />
+    </div>
+  );
+}
+```
+
+```jsx
+function Component() {
+  const MemoizedNestedComponent = React.useCallback(() => <div />, []);
+
+  return (
+    <div>
+      <MemoizedNestedComponent />
+    </div>
+  );
+}
+```
+
+```jsx
+function Component() {
+  return (
+    <SomeComponent footer={<div />} />
+  )
+}
+```
+
+By default component creation is allowed inside component props only if prop name starts with `render`. See `allowAsProps` option for disabling this limitation completely.
+
+```jsx
+function SomeComponent(props) {
+  return <div>{props.renderFooter()}</div>;
+}
+
+function Component() {
+  return (
+    <div>
+      <SomeComponent renderFooter={() => <div />} />
+    </div>
+  );
+}
+```
+
+## Rule Options
+
+```js
+...
+"react/no-unstable-nested-components": [
+  "off" | "warn" | "error",
+  { "allowAsProps": true | false }
+]
+...
+```
+
+You can allow component creation inside component props by setting `allowAsProps` option to true. When using this option make sure you are **calling** the props in the receiving component and not using them as elements.
+
+The following patterns are **not** considered warnings:
+
+```jsx
+function SomeComponent(props) {
+  return <div>{props.footer()}</div>;
+}
+
+function Component() {
+  return (
+    <div>
+      <SomeComponent footer={() => <div />} />
+    </div>
+  );
+}
+```
+
+## When Not To Use It
+
+If you are not interested in preventing bugs related to re-creation of the nested components or do not care about optimization of virtual DOM.

index.js

@@ -74,6 +74,7 @@ const allRules = {
   'no-unescaped-entities': require('./lib/rules/no-unescaped-entities'),
   'no-unknown-property': require('./lib/rules/no-unknown-property'),
   'no-unsafe': require('./lib/rules/no-unsafe'),
+  'no-unstable-nested-components': require('./lib/rules/no-unstable-nested-components'),
   'no-unused-prop-types': require('./lib/rules/no-unused-prop-types'),
   'no-unused-state': require('./lib/rules/no-unused-state'),
   'no-will-update-set-state': require('./lib/rules/no-will-update-set-state'),