feat: allow parallel option to be an integer (#3864)

closes #3850

packages/@vue/cli-plugin-babel/index.js

@@ -16,7 +16,7 @@ function genTranspileDepRegex (transpileDependencies) {
 }
 
 module.exports = (api, options) => {
-  const useThreads = process.env.NODE_ENV === 'production' && options.parallel
+  const useThreads = process.env.NODE_ENV === 'production' && !!options.parallel
   const cliServicePath = require('path').dirname(require.resolve('@vue/cli-service'))
   const transpileDepRegex = genTranspileDepRegex(options.transpileDependencies)
 
@@ -59,9 +59,13 @@ module.exports = (api, options) => {
           .end()
 
     if (useThreads) {
-      jsRule
+      const threadLoaderConfig = jsRule
         .use('thread-loader')
           .loader('thread-loader')
+
+      if (typeof options.parallel === 'number') {
+        threadLoaderConfig.options({ workers: options.parallel })
+      }
     }
 
     jsRule

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

@@ -2,7 +2,7 @@ const path = require('path')
 
 module.exports = (api, options) => {
   const fs = require('fs')
-  const useThreads = process.env.NODE_ENV === 'production' && options.parallel
+  const useThreads = process.env.NODE_ENV === 'production' && !!options.parallel
 
   api.chainWebpack(config => {
     config.resolveLoader.modules.prepend(path.join(__dirname, 'node_modules'))
@@ -37,7 +37,11 @@ module.exports = (api, options) => {
 
     if (useThreads) {
       addLoader({
-        loader: 'thread-loader'
+        loader: 'thread-loader',
+        options:
+          typeof options.parallel === 'number'
+            ? { workers: options.parallel }
+            : {}
       })
     }
 

packages/@vue/cli-service/lib/options.js

@@ -10,7 +10,10 @@ const schema = createSchema(joi => joi.object({
   runtimeCompiler: joi.boolean(),
   transpileDependencies: joi.array(),
   productionSourceMap: joi.boolean(),
-  parallel: joi.boolean(),
+  parallel: joi.alternatives().try([
+    joi.boolean(),
+    joi.number().integer()
+  ]),
   devServer: joi.object(),
   pages: joi.object().pattern(
     /\w+/,

packages/@vue/cli-service/types/ProjectOptions.d.ts

@@ -38,7 +38,7 @@ export interface ProjectOptions {
   runtimeCompiler?: boolean;
   transpileDependencies?: Array<string | RegExp>;
   productionSourceMap?: boolean;
-  parallel?: boolean;
+  parallel?: boolean | number;
   devServer?: object;
   pages?: {
     [key: string]: PageEntry | PageConfig;