feat(css): allow to use default and named export

[alexander-akait]

What kind of change does this PR introduce?

feature - allow to use default and named export

The same as requested here - webpack-contrib/mini-css-extract-plugin#1084

/cc @ahabhgk What do you think about it?

The main idea - allow to easy migrate from default to named, by default it is disabled (because we use only named export), but if developers have a lot of code, it is not easy to migrate fast, so developer can disable named export and use both of them

Did you add tests for your changes?

Yes

Does this PR introduce a breaking change?

No

What needs to be documented once your changes are merged?

When named export is disabled for CSS modules you can get classes using (we redirect named export for better DX, it will allow to migrate from default export to named smoothly):

import * as styles from "./styles.css";
import styles1 from "./styles.css";
import { foo } from "./styles.css";

console.log(styles.default.foo);
console.log(styles.foo);
console.log(styles1.foo);
console.log(foo);

When namedExport: true, you can use only named export.

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[ahabhgk]

Good idea, looks good to me

[webpack-bot]

I've created an issue to document this in webpack/webpack.js.org.

[nyngwang]

@alexander-akait Do we need to update any option from css-loader, e.g. the option modules.namedExport? Do we need to ensure it's set to true to work correctly?

[alexander-akait]

@nyngwang Yeah, let's check it and add tests, anyway I want to make namedExport to true by default in css-loader in the next major release (we should start to migrate to the named export), just want to finish webpack-contrib/css-loader#1532 (will be glad with help) before make a major release