Upgrade Babel to 8 and move polyfill injection to babel-plugin-polyfill-corejs3

Babel 8 removes preset-env's `useBuiltIns`. Each of the three configs that set
it keeps its injection mode: `entry-global` for the core polyfills bundle and
Jest, `usage-global` for the sandbox. The core-js version hint moves with it,
onto the plugin's `version` option.

core-js unifies on the catalog at 3.49.0 — 3.50.0 is inside the 7-day
`minimumReleaseAge` window. 300 -> 327 generated modules; all 38 removals are
proposals that graduated to `es.*` in the same diff.

Consequences of the major:

- `vue-jest@3` reaches @babel/core through the `babel-core` bridge, which dies
  under 8. `@vue/vue2-jest` delegates to babel-jest instead.
- transform-runtime needs an explicit `moduleName`: polyfill-corejs3 advertises
  `@babel/runtime-corejs3` as the helper module whatever its `method`.
- `@babel/parser` is pinned to 7.x inside recast's scope — recast requires it
  from CJS without declaring it, and 8.x is ESM-only.
- `@babel/plugin-syntax-import-assertions` is dropped; it has no 8.x release,
  and nothing transformed here uses import attributes.

polyfillLoader.js's comment claimed browsers passing its ES2023 array-method
test support the full polyfill set. That was already false at 3.31; the comment
now states the test as the legacy-cohort cutoff it is.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: rtibblesbot

kolibri/core/buildConfig.js

@@ -30,14 +30,10 @@ module.exports = [
             include: [path.resolve(__dirname, 'frontend/polyfills.js')],
             loader: 'babel-loader',
             options: {
-              presets: [
-                [
-                  '@babel/preset-env',
-                  {
-                    useBuiltIns: 'entry',
-                    corejs: '3.31',
-                  },
-                ],
+              presets: ['@babel/preset-env'],
+              // `version` must track the `core-js` catalog entry in pnpm-workspace.yaml.
+              plugins: [
+                ['babel-plugin-polyfill-corejs3', { method: 'entry-global', version: '3.49' }],
               ],
               sourceType: 'unambiguous',
             },

kolibri/core/frontend/polyfillLoader.js

@@ -1,9 +1,6 @@
-// Feature test for core-js 3.31 long-pole: ES2023 Array copy methods
-// (Array.prototype.toSorted / toReversed / toSpliced / with).
-// All browsers that natively support these also support the full
-// core-js 3.31 polyfill set — no generation from core-js-compat needed.
-// The pinned core-js version is corejs: '3.31' in kolibri/core/buildConfig.js —
-// revisit this test when bumping that value.
+// Legacy-cohort cutoff, not a completeness check: browsers that pass this
+// ES2023 Array-copy test still lack part of the bundled core-js set, and no
+// feature test separates that set cleanly at any core-js version.
 (function () {
   var p = Array.prototype;
   var methods = ['toSorted', 'toReversed', 'toSpliced', 'with'];

kolibri/core/package.json

@@ -4,10 +4,11 @@
   "private": true,
   "version": "0.0.1",
   "dependencies": {
-    "@babel/core": "^7.29.7",
-    "@babel/preset-env": "^7.29.7",
+    "@babel/core": "^8.0.0",
+    "@babel/preset-env": "^8.0.0",
     "@vueuse/core": "catalog:",
     "babel-loader": "^10.1.1",
+    "babel-plugin-polyfill-corejs3": "^1.0.0",
     "browserslist-config-kolibri": "workspace:*",
     "core-js": "catalog:",
     "kolibri": "workspace:*",

kolibri/plugins/media_player/package.json

@@ -4,7 +4,7 @@
   "private": true,
   "version": "0.0.1",
   "dependencies": {
-    "@babel/runtime": "^7.29.7",
+    "@babel/runtime": "^8.0.0",
     "@vueuse/core": "catalog:",
     "frame-throttle": "^3.0.0",
     "global": "^4.4.0",

package.json

@@ -43,8 +43,8 @@
   "devDependencies": {
     "@crowdin/cli": "^4.14.1",
     "@types/jest": "^30.0.0",
+    "@vue/vue2-jest": "^29.2.6",
     "@vueuse/shared": "^11.3.0",
-    "babel-core": "7.0.0-bridge.0",
     "babel-jest": "^30.3.0",
     "browserslist-config-kolibri": "workspace:*",
     "concurrently": "^8.0.1",
@@ -60,7 +60,6 @@
     "kolibri-logging": "workspace:*",
     "kolibri-plugin-data": "workspace:*",
     "rewire": "^6.0.0",
-    "vue-jest": "^3.0.0",
     "vue-template-compiler": "2.7.16",
     "webpack": "^5.104.0"
   },
@@ -98,14 +97,18 @@
       "vue-demi"
     ],
     "overrides": {
-      "@khanacademy/math-input>mathquill": "github:Khan/mathquill#v1.0.0",
-      "vue-jest>vue-template-es2015-compiler": "npm:vue-template-babel-compiler@^2.0.0"
+      "@khanacademy/math-input>mathquill": "github:Khan/mathquill#v1.0.0"
     },
     "packageExtensions": {
       "@khanacademy/perseus@*": {
         "dependencies": {
           "@swc/helpers": "^0.5.18"
         }
+      },
+      "recast@*": {
+        "dependencies": {
+          "@babel/parser": "^7.29.7"
+        }
       }
     }
   }

packages/kolibri-jest-config/jest.conf/babel.config.js

@@ -1,13 +1,11 @@
 module.exports = {
-  presets: [
-    [
-      '@babel/preset-env',
-      {
-        useBuiltIns: 'entry',
-        corejs: '3.31',
-      },
-    ],
+  presets: ['@babel/preset-env'],
+  // `version` must track the `core-js` catalog entry in pnpm-workspace.yaml.
+  plugins: [
+    ['babel-plugin-polyfill-corejs3', { method: 'entry-global', version: '3.49' }],
+    // polyfill-corejs3 advertises `@babel/runtime-corejs3` as the helper module
+    // whatever its `method`, and transform-runtime follows that over its default.
+    ['@babel/plugin-transform-runtime', { moduleName: '@babel/runtime' }],
   ],
-  plugins: ['@babel/plugin-syntax-import-assertions', '@babel/plugin-transform-runtime'],
   sourceType: 'unambiguous',
 };

packages/kolibri-jest-config/jest.conf/index.js

@@ -1,5 +1,4 @@
 const path = require('node:path');
-const babelConfig = require('./babel.config');
 
 const moduleNameMapper = {
   '^testUtils$': path.resolve(__dirname, './testUtils'),
@@ -13,9 +12,6 @@ module.exports = {
     __version: 'testversion',
     __copyrightYear: '2018',
     __webpack_public_path__: 'webpack_public_path',
-    'vue-jest': {
-      babelConfig,
-    },
   },
   rootDir: path.resolve(process.cwd()),
   moduleFileExtensions: ['js', 'json', 'vue'],
@@ -26,7 +22,7 @@ module.exports = {
   },
   transform: {
     '^.+\\.js$': 'babel-jest',
-    '^.+\\.vue$': 'vue-jest',
+    '^.+\\.vue$': '@vue/vue2-jest',
   },
   transformIgnorePatterns: [
     // Ignore all node_modules except kolibri packages

packages/kolibri-jest-config/package.json

@@ -12,12 +12,13 @@
   "private": false,
   "main": "jest.conf/index.js",
   "dependencies": {
-    "@babel/core": "^7.29.7",
-    "@babel/plugin-syntax-import-assertions": "^7.29.7",
-    "@babel/plugin-transform-runtime": "^7.29.7",
-    "@babel/preset-env": "^7.29.7",
+    "@babel/core": "^8.0.0",
+    "@babel/plugin-transform-runtime": "^8.0.0",
+    "@babel/preset-env": "^8.0.0",
+    "@babel/runtime": "^8.0.0",
     "aphrodite": "^2.4.0",
-    "core-js": "^3",
+    "babel-plugin-polyfill-corejs3": "^1.0.0",
+    "core-js": "catalog:",
     "intl": "^1.2.4",
     "kolibri": "workspace:*",
     "kolibri-design-system": "catalog:",
@@ -36,11 +37,11 @@
     "@testing-library/user-event": "^14.6.1",
     "@testing-library/vue": "^5",
     "@vue/test-utils": "^1.3.6",
+    "@vue/vue2-jest": "^29.2.6",
     "babel-jest": "^30.2.0",
     "jest": "^30.2.0",
     "jest-environment-jsdom": "^30.2.0",
-    "jest-serializer-vue": "^3.1.0",
-    "vue-jest": "^3.0.0"
+    "jest-serializer-vue": "^3.1.0"
   },
   "engines": {
     "node": ">= 20.19.0",

packages/kolibri-sandbox/babel.config.js

@@ -1,12 +1,6 @@
 /* eslint-disable import-x/no-commonjs, import-x/no-amd, import-x/no-import-module-exports */
 module.exports = {
-  presets: [
-    [
-      '@babel/preset-env',
-      {
-        useBuiltIns: 'usage',
-        corejs: '3.46',
-      },
-    ],
-  ],
+  presets: ['@babel/preset-env'],
+  // `version` must track the `core-js` catalog entry in pnpm-workspace.yaml.
+  plugins: [['babel-plugin-polyfill-corejs3', { method: 'usage-global', version: '3.49' }]],
 };

packages/kolibri-sandbox/package.json

@@ -14,9 +14,10 @@
   "author": "Learning Equality",
   "license": "MIT",
   "devDependencies": {
-    "@babel/core": "^7.29.7",
-    "@babel/preset-env": "^7.29.7",
+    "@babel/core": "^8.0.0",
+    "@babel/preset-env": "^8.0.0",
     "babel-loader": "^10.1.1",
+    "babel-plugin-polyfill-corejs3": "^1.0.0",
     "css-loader": "7.1.2",
     "css-minimizer-webpack-plugin": "8.0.0",
     "eslint-plugin-compat": "^6.0.2",
@@ -31,7 +32,7 @@
     "webpack-cli": "^7.0.2"
   },
   "dependencies": {
-    "core-js": "3.47",
+    "core-js": "catalog:",
     "dayjs": "^1.11.20",
     "iri": "^1.3.1",
     "is-language-code": "^3.1.0",