CSS Problem on --prod build when use custom-webpack

[lihuabest]

use @angular-builders/custom-webpack to export webpack.config.js hook，src/styles.css can't build with ng build --prod. @angular/cli version is @angular/cli": "~8.2.2, even i test latest.

styles has no name and no file. this is simple code of webpack.config.js
`
const path = require('path');

module.exports = (config, options) => {
config.plugins.push(spritePlugin);

  config.module.rules = config.module.rules.filter(
    rule => rule.test.toString() !== '/\\.css$/'
);

// CSS Module support
config.module.rules.push({
    test: /\.(css)$/,
    use: [
        'style-loader',
        'css-loader',
    ],
});

return config

};

`

code can't run with ng build --prod，to fix the problem i use ng build --extract-css=false， but lose some of performance. export webpack config, we can do more things like use postcss...

[clydin]

Third party builders are not supported by the Angular team. If you are encountering issues while using one please contact the author of the builder. In this case, the project can be found here: https://github.com/just-jeb/angular-builders/tree/master/packages/custom-webpack

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