Sass-loader error 'options has an unknown property 'indentedSyntax'' when upgrading Vuetify from 1.5 to 2

Question

I am upgrading Vuetify in my Vue CLI 3 project from version 1.5 to 2. I have followed these instructions, doing a full install. Since the upgrade, running 'npm run serve' gives me a ton of errors looking like this:

error  in ./node_modules/vuetify/src/components/VGrid/_grid.sass

Module build failed (from ./node_modules/sass-loader/dist/cjs.js):
    ValidationError: Invalid options object. Sass Loader has been initialised using an options object that does not match the API schema.
     - options has an unknown property 'indentedSyntax'. These properties are valid:
       object { implementation?, sassOptions?, prependData?, sourceMap?, webpackImporter? }
        at validate (C:\Users\kristoffer.dahl\Documents\Prosjekter\fridgein\fridgein_fe\node_modules\sass-loader\node_modules\schema-utils\dist\validate.js:50:11)
        at Object.loader (C:\Users\kristoffer.dahl\Documents\Prosjekter\fridgein\fridgein_fe\node_modules\sass-loader\dist\index.js:36:28)

All errors look the same, except for the Vuetify component mentioned.

This is my package.json:

{
  "name": "fridgein_fe",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "serve": "vue-cli-service serve",
    "build": "vue-cli-service build",
    "lint": "vue-cli-service lint"
  },
  "dependencies": {
    "@fortawesome/fontawesome-svg-core": "^1.2.22",
    "@fortawesome/free-brands-svg-icons": "^5.10.2",
    "@fortawesome/free-regular-svg-icons": "^5.10.2",
    "@fortawesome/free-solid-svg-icons": "^5.10.2",
    "@fortawesome/vue-fontawesome": "^0.1.7",
    "@vue/cli": "^3.11.0",
    "@vue/cli-shared-utils": "^3.11.0",
    "auth0-js": "^9.11.3",
    "axios": "^0.18.1",
    "dotenv": "^8.1.0",
    "es6-promise": "^4.2.8",
    "jquery": "^3.4.1",
    "js-cookie": "^2.2.1",
    "popper.js": "^1.14.7",
    "register-service-worker": "^1.6.2",
    "sockjs-client": "^1.3.0",
    "vue": "^2.6.10",
    "vue-float-action-button": "^0.4.4",
    "vue-google-charts": "^0.3.2",
    "vue-plugin-load-script": "^1.2.0",
    "vue-router": "^3.0.2",
    "vuetify": "^2.1.0",
    "vuex": "^3.1.1",
    "vuex-persistedstate": "^2.5.4",
    "webstomp-client": "^1.2.6"
  },
  "devDependencies": {
    "@vue/cli-plugin-babel": "^3.4.0",
    "@vue/cli-plugin-eslint": "^3.4.0",
    "@vue/cli-plugin-pwa": "^3.11.0",
    "@vue/cli-service": "^3.5.1",
    "babel-eslint": "^10.0.1",
    "babel-plugin-module-resolver": "^3.2.0",
    "css-loader": "^2.1.1",
    "deepmerge": "^4.0.0",
    "eslint": "^5.0.0",
    "eslint-plugin-vue": "^5.2.3",
    "eslint-plugin-vuetify": "^1.0.0-beta.3",
    "fibers": "^4.0.1",
    "sass": "^1.23.0",
    "sass-loader": "^8.0.0",
    "stylus": "^0.54.5",
    "stylus-loader": "^3.0.1",
    "vue-cli-plugin-vuetify": "^0.5.0",
    "vue-template-compiler": "^2.6.10",
    "vuetify-loader": "^1.3.0",
    "webpack": "^4.41.0"
  },

This is my vue.config.js:

module.exports = {
    css: {
      loaderOptions: {
        sass: {
          data: `@import "~@/sass/main.scss"`
        },
      },
    },
}

I have checked out and tried every solution presented in relevant issues on the developers' Github pages, but none has has any effect.

Has anyone else encountered this?

Answer 1

Update for those using version 10+. prependData is no longer valid. However you can use additionalData as a drop-in replacement.

Answer 2

I had the same issue and fixed it by downgrading sass-loader by setting

"sass-loader": "7.3.1",

in package.json.

This was suggested on the Vuetify Discord

Answer 3

Actually you are using sass-loader 8+ and it has an option a little bit different.
Try using prependData instead of data.
Check this github issue

module.exports = {
    css: {
      loaderOptions: {
        sass: {
          prependData: `@import "~@/sass/main.scss"`
        }
      }
    }
}