This plugin is deprecated in favor of styled-components/babel-plugin-styled-components#248. It's possible that something other than styled-components might cause a similar issue, in which case this plugin might still be useful, but I won't be maintaining it. (Also, my implementation for babel-plugin-styled-components is a bit more efficient than what I did here.)
Fixes an issue with tree shaking that can occur when using static properties on React components using styled-components.
This plugin replaces static property assignments on React components (e.g. MyComponent.defaultProps = {...}) with Object.assign() statements annotated with /*#__PURE__*/ comments so that tree-shaking will work correctly.