New: Add require-default-props rule (fixes #528)

Author: vitorbal

README.md

@@ -103,6 +103,7 @@ Finally, enable all of the rules that you would like to use.  Use [our preset](#
 * [react/prefer-stateless-function](docs/rules/prefer-stateless-function.md): Enforce stateless React Components to be written as a pure function
 * [react/prop-types](docs/rules/prop-types.md): Prevent missing props validation in a React component definition
 * [react/react-in-jsx-scope](docs/rules/react-in-jsx-scope.md): Prevent missing `React` when using JSX
+* [react/require-default-props](docs/rules/require-default-props.md): Enforce a defaultProps definition for every prop that is not a required prop
 * [react/require-optimization](docs/rules/require-optimization.md): Enforce React components to have a shouldComponentUpdate method
 * [react/require-render-return](docs/rules/require-render-return.md): Enforce ES5 or ES6 class for returning value in render function
 * [react/self-closing-comp](docs/rules/self-closing-comp.md): Prevent extra closing tags for components without children (fixable)

docs/rules/require-default-props.md

@@ -0,0 +1,163 @@
+# Enforce a defaultProps definition for every prop that is not a required prop (require-default-props)
+
+This rule aims to ensure that any non-required `PropType` declaration of a component has a corresponding `defaultProps` value.
+
+One advantage of `defaultProps` over regular default logic in your code is that `defaultProps` are resolved by React before the `PropTypes` typechecking happens, so typechecking will also apply to your `defaultProps`.
+
+To illustrate, consider the following example:
+
+With `defaultProps`:
+```js
+const HelloWorld = ({ name }) => (
+  <h1>Hello, {name.first} {name.last}!</h1>
+);
+
+HelloWorld.propTypes = {
+  name: React.PropTypes.shape({
+    first: React.PropTypes.string,
+    last: React.PropTypes.string,
+  })
+};
+
+HelloWorld.defaultProps = {
+  name: 'john'
+};
+
+// Logs:
+// Invalid prop `name` of type `string` supplied to `HelloWorld`, expected `object`.
+ReactDOM.render(<HelloWorld />,  document.getElementById('app'));
+```
+
+Without `defaultProps`:
+```js
+const HelloWorld = ({ name = 'John Doe' }) => (
+  <h1>Hello, {name.first} {name.last}!</h1>
+);
+
+HelloWorld.propTypes = {
+  name: React.PropTypes.shape({
+    first: React.PropTypes.string,
+    last: React.PropTypes.string,
+  })
+};
+
+// Nothing is logged, renders:
+// "Hello,!"
+ReactDOM.render(<HelloWorld />,  document.getElementById('app'));
+```
+
+## Rule Details
+
+The following patterns are considered warnings:
+
+```js
+function MyStatelessComponent({ foo, bar }) {
+  return <div>{foo}{bar}</div>;
+}
+
+MyStatelessComponent.propTypes = {
+  foo: React.PropTypes.string.isRequired,
+  bar: React.PropTypes.string
+};
+```
+
+```js
+var Greeting = React.createClass({
+  render: function() {
+    return <div>Hello {this.props.foo} {this.props.bar}</div>;
+  },
+
+  propTypes: {
+    foo: React.PropTypes.string,
+    bar: React.PropTypes.string
+  },
+
+  getDefaultProps: function() {
+    return {
+      foo: "foo"
+    };
+  }
+});
+```
+
+```js
+class Greeting extends React.Component {
+  render() {
+    return (
+      <h1>Hello, {this.props.foo} {this.props.bar}</h1>
+    );
+  }
+}
+
+Greeting.propTypes = {
+  foo: React.PropTypes.string,
+  bar: React.PropTypes.string
+};
+
+Greeting.defaultProps = {
+  foo: "foo"
+};
+```
+
+```js
+class Greeting extends React.Component {
+  render() {
+    return (
+      <h1>Hello, {this.props.foo} {this.props.bar}</h1>
+    );
+  }
+
+  static propTypes = {
+    foo: React.PropTypes.string,
+    bar: React.PropTypes.string.isRequired
+  };
+
+  static defaultProps = {
+    foo: "foo"
+  };
+}
+```
+
+The following patterns are not considered warnings:
+
+```js
+function MyStatelessComponent({ foo, bar }) {
+  return <div>{foo}{bar}</div>;
+}
+
+MyStatelessComponent.propTypes = {
+  foo: React.PropTypes.string.isRequired,
+  bar: React.PropTypes.string.isRequired
+};
+```
+
+```js
+function MyStatelessComponent({ foo, bar }) {
+  return <div>{foo}{bar}</div>;
+}
+
+MyStatelessComponent.propTypes = {
+  foo: React.PropTypes.string.isRequired,
+  bar: React.PropTypes.string
+};
+
+MyStatelessComponent.defaultProps = {
+    bar: 'some default'
+};
+```
+
+```js
+function NotAComponent({ foo, bar }) {}
+
+NotAComponent.propTypes = {
+  foo: React.PropTypes.string,
+  bar: React.PropTypes.string.isRequired
+};
+```
+
+## When Not To Use It
+
+If you don't care about using `defaultsProps` for your component's props that are not required, you can disable this rule.
+
+# Resources
+- [Official React documentation on defaultProps](https://facebook.github.io/react/docs/typechecking-with-proptypes.html#default-prop-values)

index.js

@@ -4,6 +4,7 @@ var allRules = {
   'jsx-uses-react': require('./lib/rules/jsx-uses-react'),
   'no-multi-comp': require('./lib/rules/no-multi-comp'),
   'prop-types': require('./lib/rules/prop-types'),
+  'require-default-props': require('./lib/rules/require-default-props'),
   'display-name': require('./lib/rules/display-name'),
   'jsx-wrap-multilines': require('./lib/rules/jsx-wrap-multilines'),
   'self-closing-comp': require('./lib/rules/self-closing-comp'),