CSS Loader has been initialised using an options object that does not match the API schema

Question

Production build fails with the following error:

ValidationError: Invalid options object. CSS Loader has been initialised using an options object that does not match the API schema.
 - options has an unknown property 'minimize'. These properties are valid:
   object { url?, import?, modules?, sourceMap?, importLoaders?, localsConvention?, onlyLocals? }
    at validate (/Users/username/Sites/projectname/node_modules/css-loader/node_modules/schema-utils/dist/validate.js:85:11)
    at Object.loader (/Users/username/Sites/projectname/node_modules/css-loader/dist/index.js:34:28)

Using this webpack template: http://vuejs-templates.github.io/webpack/, updated to Webpack 4 and faced build issues, package.json:

{
  "name": "projectname",
  "private": true,
  "scripts": {
    "dev": "webpack-dev-server --inline --progress --config webpack.config.js --port 3000 --hot",
    "start": "npm run dev",
    "build": "cross-env NODE_ENV=production webpack --progress --hide-modules"
  },
  "dependencies": {
    "@vue/cli-service": "^3.2.0",
    "axios": "^0.18.0",
    "babel-polyfill": "^6.26.0",
    "cross-env": "^5.2.0",
    "css-loader": "^3.2.1",
    "jquery": "^3.3.1",
    "moment": "^2.22.2",
    "style-loader": "^1.0.1",
    "swiper": "^4.5.0",
    "v-tabs-router": "^1.4.0",
    "vee-validate": "^2.1.0-beta.9",
    "vue": "^2.5.2",
    "vue-awesome-swiper": "^3.1.3",
    "vue-backtotop": "^1.6.1",
    "vue-carousel": "^0.18.0",
    "vue-cleave-component": "^2.1.2",
    "vue-instant": "^1.0.2",
    "vue-jsonp": "^0.1.8",
    "vue-magic-line": "^0.2.1",
    "vue-masked-input": "^0.5.2",
    "vue-resource": "^1.5.1",
    "vue-router": "^3.0.2",
    "vue-select": "^2.5.1",
    "vue-slider-component": "^2.8.0",
    "vue-smooth-scroll": "^1.0.13",
    "vuejs-datepicker": "^1.5.3",
    "vuelidate": "^0.7.4",
    "vuex": "^3.0.1"
  },
  "devDependencies": {
    "autoprefixer": "^7.1.2",
    "babel-core": "^6.22.1",
    "babel-helper-vue-jsx-merge-props": "^2.0.3",
    "babel-loader": "^7.1.1",
    "babel-plugin-syntax-jsx": "^6.18.0",
    "babel-plugin-transform-runtime": "^6.22.0",
    "babel-plugin-transform-vue-jsx": "^3.5.0",
    "babel-preset-env": "^1.3.2",
    "babel-preset-stage-2": "^6.22.0",
    "chalk": "^2.0.1",
    "copy-webpack-plugin": "^4.0.1",
    "extract-text-webpack-plugin": "^3.0.0",
    "file-loader": "^5.0.2",
    "friendly-errors-webpack-plugin": "^1.6.1",
    "html-webpack-plugin": "^3.2.0",
    "node-notifier": "^5.1.2",
    "node-sass": "^4.13.0",
    "optimize-css-assets-webpack-plugin": "^5.0.3",
    "ora": "^1.2.0",
    "portfinder": "^1.0.13",
    "postcss-import": "^12.0.1",
    "postcss-loader": "^3.0.0",
    "postcss-url": "^8.0.0",
    "rimraf": "^2.6.0",
    "sass-loader": "^8.0.0",
    "semver": "^5.3.0",
    "shelljs": "^0.7.6",
    "uglifyjs-webpack-plugin": "^1.1.1",
    "url-loader": "^1.1.2",
    "vue-loader": "^14.2.2",
    "vue-resource": "^1.5.1",
    "vue-style-loader": "^4.1.2",
    "vue-template-compiler": "^2.5.2",
    "webpack": "^4.41.2",
    "webpack-cli": "^3.3.10",
    "webpack-dev-server": "^3.9.0"
  },
  "engines": {
    "node": ">= 6.0.0",
    "npm": ">= 3.0.0"
  },
  "browserslist": [
    "> 1%",
    "last 2 versions",
    "not ie <= 8"
  ]
}

I've checked with grep -rl 'minimize' . in a project root, but didn't found any related options. Wth..

Answer 1

This has to do with a breaking change in the module. According to semver rules, a major change (first digit x of version x.y.z) is a breaking change.

In this case the old version syntax uses

    {
        loader: 'postcss-loader',
        options: {
            plugins: postCSSPlugins
        }
    }

whereas the new version in options uses nested postcssOptions before plugins

    {
        loader: 'postcss-loader',
        options: {
            postcssOptions: {
                plugins: postCSSPlugins
            }
        }
    }

Answer 2

I also encountered this error when updating to webpack 4 and using MiniCssExtractPlugin

I was able to eliminate the error and get a successful build by using an older version of ccs-loader

These versions worked for me

 "devDependencies": {
   "css-loader": "1.0.1",

OR

   "css-loader": "^0.28.0",

css-loader 2* and 3* gave me the error.

UPDATE after testing publish: using the old version of the css-loader causes the css to fail to load when rendering the web site in a browser. So this appears to not be a solution.