@vue/cli-plugin-typescript/index.js

const path = require('path')

module.exports = (api, projectOptions) => {
  const fs = require('fs')
  const useThreads = process.env.NODE_ENV === 'production' && !!projectOptions.parallel

  const { semver, loadModule } = require('@vue/cli-shared-utils')
  const vue = loadModule('vue', api.service.context)
  const isVue3 = (vue && semver.major(vue.version) === 3)

  api.chainWebpack(config => {
    config.resolveLoader.modules.prepend(path.join(__dirname, 'node_modules'))

    if (!projectOptions.pages) {
      config.entry('app')
        .clear()
        .add('./src/main.ts')
    }

    config.resolve
      .extensions
        .prepend('.ts')
        .prepend('.tsx')

    const tsRule = config.module.rule('ts').test(/\.ts$/)
    const tsxRule = config.module.rule('tsx').test(/\.tsx$/)

    // add a loader to both *.ts & vue<lang="ts">
    const addLoader = ({ name, loader, options }) => {
      tsRule.use(name).loader(loader).options(options)
      tsxRule.use(name).loader(loader).options(options)
    }

    addLoader({
      name: 'cache-loader',
      loader: require.resolve('cache-loader'),
      options: api.genCacheConfig('ts-loader', {
        'ts-loader': require('ts-loader/package.json').version,
        'typescript': require('typescript/package.json').version,
        modern: !!process.env.VUE_CLI_MODERN_BUILD
      }, 'tsconfig.json')
    })

    if (useThreads) {
      addLoader({
        name: 'thread-loader',
        loader: require.resolve('thread-loader'),
        options:
          typeof projectOptions.parallel === 'number'
            ? { workers: projectOptions.parallel }
            : {}
      })
    }

    if (api.hasPlugin('babel')) {
      addLoader({
        // TODO: I guess the intent is to require the `babel-loader` provided by the Babel vue
        // plugin, but that means we now rely on the hoisting. It should instead be queried
        // against the plugin itself, or through a peer dependency.
        name: 'babel-loader',
        // eslint-disable-next-line node/no-extraneous-require
        loader: require.resolve('babel-loader')
      })
    }
    addLoader({
      name: 'ts-loader',
      loader: require.resolve('ts-loader'),
      options: {
        transpileOnly: true,
        appendTsSuffixTo: ['\\.vue$'],
        // https://github.com/TypeStrong/ts-loader#happypackmode-boolean-defaultfalse
        happyPackMode: useThreads
      }
    })
    // make sure to append TSX suffix
    tsxRule.use('ts-loader').loader(require.resolve('ts-loader')).tap(options => {
      options = Object.assign({}, options)
      delete options.appendTsSuffixTo
      options.appendTsxSuffixTo = ['\\.vue$']
      return options
    })

    // this plugin does not play well with jest + cypress setup (tsPluginE2e.spec.js) somehow
    // so temporarily disabled for vue-cli tests
    if (!process.env.VUE_CLI_TEST) {
      if (isVue3) {
        config
          .plugin('fork-ts-checker')
          .use(require('fork-ts-checker-webpack-plugin-v5'), [{
            typescript: {
              extensions: {
                vue: {
                  enabled: true,
                  compiler: '@vue/compiler-sfc'
                }
              },
              diagnosticOptions: {
                semantic: true,
                // https://github.com/TypeStrong/ts-loader#happypackmode
                syntactic: useThreads
              }
            }
          }])
      } else {
        config
          .plugin('fork-ts-checker')
            .use(require('fork-ts-checker-webpack-plugin'), [{
              vue: { enabled: true, compiler: 'vue-template-compiler' },
              tslint: projectOptions.lintOnSave !== false && fs.existsSync(api.resolve('tslint.json')),
              formatter: 'codeframe',
              // https://github.com/TypeStrong/ts-loader#happypackmode-boolean-defaultfalse
              checkSyntacticErrors: useThreads
            }])
      }
    }
  })

  if (!api.hasPlugin('eslint')) {
    api.registerCommand('lint', {
      description: 'lint source files with TSLint',
      usage: 'vue-cli-service lint [options] [...files]',
      options: {
        '--format [formatter]': 'specify formatter (default: codeFrame)',
        '--no-fix': 'do not fix errors',
        '--formatters-dir [dir]': 'formatter directory',
        '--rules-dir [dir]': 'rules directory'
      }
    }, args => {
      return require('./lib/tslint')(args, api)
    })
  }
}