Extremely long compile times with Vuetify 2.1 and Webpack

Question

I am using Vue CLI 3 and Vuetify 2.1 in a new-ish project, and recently delved into overriding Vuetify's SASS variables. After finally getting it to work, I realized that each time I modify the variables.scss file that I created and the project recompiles, it takes close to 5 minutes to finish compiling. I've tried updating the package.json script to bump up the memory that Node is using, and while that fixed an error I was receiving that caused the compile to crash, the result is now extremely slow compile times. The progress that shows (I'm using Foreman to run both my Rails API and Vue server at the same time) looks like this:

17:47:29 web.1  | <s> [webpack.Progress] 69% building 916/930 modules 14 active /<path/to/app>/frontend/node_modules/css-loader/index.js??ref--9-oneOf-3-1!/<path/to/app>/frontend/node_modules/postcss-loader/src/index.js??ref--9-oneOf-3-2!/<path/to/app>/frontend/node_modules/sass-loader/lib/loader.js??ref--9-oneOf-3-3!/<path/to/app>/frontend/node_modules/vuetify/src/components/VSwitch/VSwitch.sass

These progresses load, like I mentioned, for about five minutes before it finally finishes. My guess is that because I updated a variable, it's having to go through and update that style for each component and instance of that variable in the Vuetify node_module.

My question is whether there is any way to speed this up? Maybe I've set something up wrong that has caused this issue? Or is this totally normal and I'll just have to deal with it?

main.js

import Vue from 'vue';

import App from './App.vue';
import { router } from './router';
import store from './_store';
import vuetify from './plugins/vuetify';

Vue.config.productionTip = false;

new Vue({
  router,
  store,
  vuetify,
  render: h => h(App),
}).$mount('#app');

vuetify.js

import 'material-design-icons-iconfont/dist/material-design-icons.css';
import Vue from 'vue';
import Vuetify from 'vuetify/lib';

Vue.use(Vuetify);

export default new Vuetify({
  theme: {
    options: {
      customProperties: true,
    },
    themes: {
      light: {
        primary: '#4A90E2',
        darkPrimary: '#3B73B4',
        secondary: '#424242',
        accent: '#82B1FF',
        error: '#a70000',
        info: '#2196F3',
        success: '#4CAF50',
        warning: '#FFC107',
        teal: '#64EBC6',
        green: '#7ED321',
        darkGreen: '#4c8f1d',
        lightGrey: 'rgba(0,0,0,0.12)',
        darkGrey: '#4A4A4A',
        textSecondary: 'rgba(0,0,0,0.4)',
      },
    },
  },
  icons: {
    iconfont: 'md',
  },
});

variables.scss

// Globals
$border-radius-root: 2px;
// $font-size-root: 14px;
$body-font-family: 'Avenir Next', 'Lato', Roboto, 'Helvetica Neue', Helvetica, Arial, sans-serif; // $main-font comes from my own ./_variables.scss.
$heading-font-family: 'Avenir Next', 'Lato', Roboto, 'Helvetica Neue', Helvetica, Arial, sans-serif; // $title-font comes from my own ./_variables.scss.

$headings: (
  'h1': (
    'size': 3.3125rem,
    'line-height': 1.15em
  ),
  'h2': (
    'size': 2.25rem,
    'line-height': 1.5em,
  ),
  'h3': (
    'size': 1.5625rem,
    'line-height': 1.4em
  ),
  'h4': (
    'size': 1.125rem,
    'line-height': 1.4em
  ),
  'h5': (
    'size': 1.0625rem
  ),
  'h6': (
    'size': .75rem
  ),
  'subtitle-2': (
    'size': 1rem
  ),
  'overline': (
    'letter-spacing': 0
  )
);

@import '~vuetify/src/styles/settings/variables';

// V-Btn
$btn-letter-spacing: 1px;
@import '~vuetify/src/components/VBtn/_variables';

@import '~vuetify/src/styles/main.sass';

package.json

{
  "name": "myProject",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "serve" : "node --max_old_space_size=4096 node_modules/.bin/vue-cli-service serve",
    "build": "vue-cli-service build",
    "lint": "vue-cli-service lint"
  },
  "dependencies": {
    "axios": "^0.19.0",
    "core-js": "^2.6.5",
    "dayjs": "^1.8.16",
    "echarts": "^4.3.0",
    "fibers": "^4.0.1",
    "material-design-icons-iconfont": "^5.0.1",
    "sass": "^1.23.0",
    "sass-loader": "7.1.0",
    "vee-validate": "^3.0.11",
    "vue": "^2.6.10",
    "vue-router": "^3.0.3",
    "vuedraggable": "^2.23.2",
    "vuetify": "^2.1.0",
    "vuex": "^3.0.1"
  },
  "devDependencies": {
    "@vue/cli-plugin-babel": "^3.12.0",
    "@vue/cli-plugin-eslint": "^3.12.0",
    "@vue/cli-service": "^3.12.0",
    "@vue/eslint-config-airbnb": "^4.0.0",
    "babel-eslint": "^10.0.1",
    "eslint": "^5.16.0",
    "eslint-plugin-vue": "^5.0.0",
    "vue-cli-plugin-vuetify": "^1.0.1",
    "vue-template-compiler": "^2.6.10",
    "vuetify-loader": "^1.2.2"
  }
}

Answer 1

@import '~vuetify/src/styles/main.sass';

This injects a fairly large amount of CSS into the top of every single sass file, so it gets repeated a couple hundred times. The variables file should not contain any code that outputs actual styles - only variables, mixins, and functions are allowed.

30+ sec when modifying the variables file is normal however, as you guessed it has to recompile everything in that case. Importing from vuetify/lib/framework instead of vuetify/lib may speed this up somewhat by only including used components in the dev bundle.