Backport #30742

Update to `@rollup/plugin-babel`

build/babel-helpers.js

@@ -1,13 +0,0 @@
-'use strict'
-
-// These are the babel helpers we whitelist
-const helpers = [
-  'createClass',
-  'createSuper',
-  'defineProperties',
-  'defineProperty',
-  'inheritsLoose',
-  'objectSpread2'
-]
-
-module.exports = helpers

build/build-plugins.js

@@ -9,19 +9,18 @@
 
 'use strict'
 
-const path    = require('path')
-const rollup  = require('rollup')
-const babel   = require('rollup-plugin-babel')
-const banner  = require('./banner.js')
-const babelHelpers = require('./babel-helpers.js')
+const path = require('path')
+const rollup = require('rollup')
+const { babel } = require('@rollup/plugin-babel')
+const banner = require('./banner.js')
 
-const TEST    = process.env.NODE_ENV === 'test'
+const TEST = process.env.NODE_ENV === 'test'
 const plugins = [
   babel({
     // Only transpile our source code
     exclude: 'node_modules/**',
-    // Include only required helpers
-    externalHelpersWhitelist: babelHelpers
+    // Inline the required helpers in each file
+    babelHelpers: 'inline'
   })
 ]
 const bsPlugins = {

build/rollup.config.js

@@ -1,21 +1,20 @@
 'use strict'
 
-const path    = require('path')
-const babel   = require('rollup-plugin-babel')
+const path = require('path')
+const { babel } = require('@rollup/plugin-babel')
 const resolve = require('@rollup/plugin-node-resolve')
-const banner  = require('./banner.js')
-const babelHelpers = require('./babel-helpers.js')
+const banner = require('./banner.js')
 
-const BUNDLE  = process.env.BUNDLE === 'true'
+const BUNDLE = process.env.BUNDLE === 'true'
 
-let fileDest  = 'bootstrap.js'
+let fileDest = 'bootstrap.js'
 const external = ['jquery', 'popper.js']
 const plugins = [
   babel({
-  // Only transpile our source code
+    // Only transpile our source code
     exclude: 'node_modules/**',
-    // Include only required helpers
-    externalHelpersWhitelist: babelHelpers
+    // Include the helpers in the bundle, at most one copy of each
+    babelHelpers: 'bundled'
   })
 ]
 const globals = {