add new rule

Author: cyan33

README.md

@@ -123,6 +123,7 @@ Enable the rules that you would like to use.
 * [react/no-find-dom-node](docs/rules/no-find-dom-node.md): Prevent usage of findDOMNode
 * [react/no-is-mounted](docs/rules/no-is-mounted.md): Prevent usage of isMounted
 * [react/no-multi-comp](docs/rules/no-multi-comp.md): Prevent multiple component definition per file
+* [react/no-object-type-as-default-prop](docs/rules/no-object-type-as-default-prop.md): Prevent usage of object types variables as default param in functional component
 * [react/no-redundant-should-component-update](docs/rules/no-redundant-should-component-update.md): Flag shouldComponentUpdate when extending PureComponent
 * [react/no-render-return-value](docs/rules/no-render-return-value.md): Prevent usage of the return value of React.render
 * [react/no-set-state](docs/rules/no-set-state.md): Prevent usage of setState

docs/rules/no-object-type-as-default-prop.md

@@ -0,0 +1,68 @@
+# Prevent usage of referential-type variables as default param in functional component (react/no-object-type-as-default-prop)
+
+Warns if in a functional component, an object type value (such as array/object literal) is used as default prop, to prevent potential un-necessary re-renders, and performance regressions.
+
+## Rule Details
+
+Certain values (like arrays, objects, functions, etc) are compared by indentity instead of by value. This means that, for example, whilst two empty arrays represent the same value - to the JS engine they are distinct and inequal as they represent two different identities in memory.
+
+When using object destructuring syntax you can set the default value for a given property if it does not exist. If you set the default value to one of the values that is compared by identity, it will mean that each time the destructure is executed the JS engine will create a new, non-equal value in the destructured variable.
+
+In the  context of a React functional component's props argument this means that each render the property has a new, distinct value. When this value is passed to a hook as a dependency or passed into a child component as a property react will see this as a new value - meaning that a hook will be re-evaluated, or a memoized component will rerender.
+
+This obviously destroys any performance benefits you get from memoisation. Additionally in certain circumstances this can cause infinite rerender loops, which can often be hard to debug.
+
+It's worth noting that primitive literal values (`string`, `number`, `boolean`, `null`, and `undefined`) are equal when two same value are being compared, so it's safe for those to be inlined as default prop.
+
+To fix the violations, the easiest way is to use a referencing variable instead of using the literal values, e.g:
+
+```jsx
+const emptyArray = [];
+
+function Component({
+  items = emptyArray,
+}) {}
+```
+
+Examples of ***invalid*** code for this rule:
+
+```jsx
+function Component({
+  items = [],
+}) {}
+
+const Component = ({
+  items = {},
+}) => {}
+
+const Component = ({
+  items = () => {},
+}) => {}
+```
+
+Examples of ***valid*** code for this rule:
+
+```jsx
+const emptyArray = [];
+
+function Component({
+  items = emptyArray,
+}) {}
+
+const emptyObject = {};
+const Component = ({
+  items = emptyObject,
+}) => {}
+
+const noopFunc = () => {};
+const Component = ({
+  items = noopFunc,
+}) => {}
+
+// primitive literals are all compared by value, so are safe to be inlined
+function Component({
+  num = 3,
+  str = 'foo',
+  bool = true,
+}) {}
+```

index.js

@@ -67,6 +67,7 @@ const allRules = {
   'no-find-dom-node': require('./lib/rules/no-find-dom-node'),
   'no-is-mounted': require('./lib/rules/no-is-mounted'),
   'no-multi-comp': require('./lib/rules/no-multi-comp'),
+  'no-object-type-as-default-prop': require('./lib/rules/no-object-type-as-default-prop'),
   'no-set-state': require('./lib/rules/no-set-state'),
   'no-string-refs': require('./lib/rules/no-string-refs'),
   'no-redundant-should-component-update': require('./lib/rules/no-redundant-should-component-update'),

lib/rules/no-object-type-as-default-prop.js

@@ -0,0 +1,150 @@
+/**
+ * @fileoverview Prevent usage of referential-type variables as default param in functional component
+ * @author Chang Yan
+ */
+
+'use strict';
+
+const docsUrl = require('../util/docsUrl');
+
+const FORBIDDEN_TYPES_MAP = {
+  ArrowFunctionExpression: 'arrow function',
+  FunctionExpression: 'function expression',
+  ObjectExpression: 'object literal',
+  ArrayExpression: 'array literal',
+  ClassExpression: 'class expression',
+  NewExpression: 'construction expression',
+  JSXElement: 'JSX element'
+};
+
+const FORBIDDEN_TYPES = new Set(Object.keys(FORBIDDEN_TYPES_MAP));
+const MESSAGE_ID = 'forbiddenTypeDefaultParam';
+
+function isReactComponentName(node) {
+  if (node.id && node.id.type === 'Identifier' && node.id.name) {
+    const firstLetter = node.id.name[0];
+    if (firstLetter.toUpperCase() === firstLetter) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+function isReactComponentVariableDeclarator(variableDeclarator) {
+  if (!isReactComponentName(variableDeclarator)) {
+    return false;
+  }
+  return (
+    variableDeclarator.init != null
+    && variableDeclarator.init.type === 'ArrowFunctionExpression'
+  );
+}
+
+function hasUsedObjectDestructuringSyntax(params) {
+  if (
+    params == null
+    || params.length !== 1
+    || params[0].type !== 'ObjectPattern'
+  ) {
+    return false;
+  }
+  return true;
+}
+
+function verifyDefaultPropsDestructuring(context, properties) {
+  // Loop through each of the default params
+  properties.forEach((prop) => {
+    if (prop.type !== 'Property') {
+      return;
+    }
+
+    const propName = prop.key.name;
+    const propDefaultValue = prop.value;
+
+    if (propDefaultValue.type !== 'AssignmentPattern') {
+      return;
+    }
+
+    const propDefaultValueType = propDefaultValue.right.type;
+
+    if (
+      propDefaultValueType === 'Literal'
+      && propDefaultValue.right.regex != null
+    ) {
+      context.report({
+        node: propDefaultValue,
+        messageId: MESSAGE_ID,
+        data: {
+          propName,
+          forbiddenType: 'regex literal'
+        }
+      });
+    } else if (propDefaultValueType === 'CallExpression'
+      && propDefaultValue.right.callee.type === 'Identifier'
+      && propDefaultValue.right.callee.name === 'Symbol'
+    ) {
+      context.report({
+        node: propDefaultValue,
+        messageId: MESSAGE_ID,
+        data: {
+          propName,
+          forbiddenType: 'Symbol literal'
+        }
+      });
+    } else if (FORBIDDEN_TYPES.has(propDefaultValueType)) {
+      context.report({
+        node: propDefaultValue,
+        messageId: MESSAGE_ID,
+        data: {
+          propName,
+          forbiddenType: FORBIDDEN_TYPES_MAP[propDefaultValueType]
+        }
+      });
+    }
+  });
+}
+
+module.exports = {
+  meta: {
+    docs: {
+      description: 'Prevent usage of referential-type variables as default param in functional component',
+      category: 'Best Practices',
+      recommended: false,
+      url: docsUrl('no-object-type-as-default-prop')
+    },
+    messages: {
+      [MESSAGE_ID]:
+        '{{propName}} has a/an {{forbiddenType}} as default prop.\n'
+        + 'This could lead to potential infinite render loop in React. \n'
+        + 'Use a variable reference instead of {{forbiddenType}}.'
+    }
+  },
+  create(context) {
+    return {
+      FunctionDeclaration(node) {
+        if (
+          !isReactComponentName(node)
+          || !hasUsedObjectDestructuringSyntax(node.params)
+        ) {
+          return;
+        }
+
+        const properties = node.params[0].properties;
+        verifyDefaultPropsDestructuring(context, properties);
+      },
+      'VariableDeclarator > :matches(ArrowFunctionExpression, FunctionExpression).init'(
+        node
+      ) {
+        if (
+          !isReactComponentVariableDeclarator(node.parent)
+          || !hasUsedObjectDestructuringSyntax(node.params)
+        ) {
+          return;
+        }
+        const properties = node.params[0].properties;
+        verifyDefaultPropsDestructuring(context, properties);
+      }
+    };
+  }
+};