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

[rtibblesbot]

Summary

Injection moves off the removed useBuiltIns onto babel-plugin-polyfill-corejs3 — entry-global for the polyfills bundle and Jest, usage-global for the sandbox. core-js unifies on the catalog at 3.49.0.

References

Fixes #15138. Supersedes #15113 — close when this lands.
Criteria ticked with evidence: #15169 (comment)

Reviewer guidance

• jest.conf/babel.config.js:8 — polyfill-corejs3 advertises @babel/runtime-corejs3 whatever its method, and transform-runtime follows it; hence moduleName.
• package.json:108 — @babel/parser held at 7.x in recast's scope: 8.x is ESM-only and recast require()s it undeclared.
• jest.conf/index.js:25 — @vue/vue2-jest@29.2.6 peers jest 29 / babel-jest 29 / @babel/core 7, all mismatched.
• pnpm-lock.yaml — one non-Babel move: terser 5.49.2 → 5.46.0, deduped onto the copy already there under an optional terser-webpack-plugin.

Polyfill accounting

core-js-compat over browserslist-config-kolibri: 300 → 327 modules, 65 added, 38 removed. Every removal is an esnext.X with a matching es.X addition.

38 graduations, 27 new modules

Graduated: iterator.*, set.* v2, json.* raw-json, array-buffer.* transfer/detached, symbol.[async-]dispose, [async-]disposable-stack, async-iterator.async-dispose, suppressed-error, array.from-async, map/object.group-by, promise.try, promise.with-resolvers.

Group	New
Float16	es.data-view.{get,set}-float16, es.math.f16round
Uint8Array	es.uint8-array.{from,to,set-from}-{base64,hex}
getOrInsert	es.{map,weak-map}.get-or-insert[-computed]
Other stable	es.error.is-error, es.iterator.concat, es.math.sum-precise, es.regexp.escape
Proposals	esnext.data-view.{get,set}-uint8-clamped, esnext.iterator.{chunks,sliding,windows,zip,zip-keyed}, esnext.number.clamp, esnext.symbol.custom-matcher
Web	web.url.parse

Emitted core-js/modules/* for polyfills.js:

Step	Emitted	vs previous
Babel 7, useBuiltIns: 'entry', corejs 3.31	300	—
core-js → 3.49	327	all 103 changed ids are in the compat diff
useBuiltIns → polyfill-corejs3	327	byte-identical
Babel 7 → 8	327	identical

Bundle 211,870 → 230,596 bytes (gz 73,633 → 80,399), all the core-js bump.

Sandbox usage mode: 58 modules before and after, the one change esnext.json.parse → es.json.parse. Re-measure with babel-loader's caller flags; without them preset-env down-transforms import() and injects a spurious es.weak-map.

Criteria not met as written

1. Latest core-js — 3.49.0; minimumReleaseAge blocks 3.50.0 until 2026-08-12.
2. A feature test separating browsers that need the bundle — not achievable at any version: the cohort passing the ES2023 array-copy test needs 184 modules at 3.31 and 211 at 3.49, and no es.* module dominates all three engines. It stays a legacy-cohort cutoff — measurement.
3. Matching corejs: hints — that preset-env key is gone; the literal is polyfill-corejs3's version, '3.49' in all three configs.
4. BrowserStack Chrome 49 — unverified: no credentials or tunnel here.

Verification

pnpm test-jest 318/318, pnpm sandbox-build, make assets, make dist, prek: pass. No useBuiltIns outside node_modules.

AI usage

Used Claude Code to plan and implement the upgrade, and to measure the compat and emitted-import diffs rather than reason about them. Verified with the full Jest suite, the sandbox build and the WHL build.

---

@rtibblesbot's comments are generated by an LLM, and should be evaluated accordingly

How was this generated?

• Ran pre-flight CI checks (lint, format, tests) and verified all pass
• Rebased onto the target branch and resolved any conflicts
• Reorganized commit history into clean, logical commits
• Audited the diff to ensure only issue-relevant files are changed
• Built PR body from the repository's PR template with evidence blocks

🟡 Waiting for feedback Last updated: 2026-08-08 10:26 UTC

[github-actions]

npm Package Versions

Warning

The following packages have changed files but no version bump:

Package	Version	Changed files
kolibri-jest-config	1.0.0	3

If these changes affect published code, consider bumping the version.

[github-actions]

Build Artifacts

Asset type	Download link
PEX file	kolibri-0.20.0a1.dev13_g1850b102c.d20260808.pex
Windows Installer (EXE)	kolibri-setup-0.20.0a1.dev13+g1850b102c.d20260808-unsigned.exe
Debian Package	kolibri_0.20.0a1.dev13+g1850b102c-0ubuntu1_all.deb
Debian Package	kolibri-server_0.20.0~a1.dev13+g1850b102c-0ubuntu1_all.deb
Mac Installer (DMG)	kolibri-0.20.0a1.dev13+g1850b102c.d20260808.dmg
Android Package (APK)	kolibri-0.20.0a1.dev13+g1850b102c.d20260808-debug.apk
Raspberry Pi Image	kolibri-pi-image-0.20.0a1.dev13+g1850b102c.zip
TAR file	kolibri-0.20.0a1.dev13+g1850b102c.d20260808.tar.gz
WHL file	kolibri-0.20.0a1.dev13+g1850b102c.d20260808-py3-none-any.whl

Smoke test screenshot

Download screenshot

[rtibblesbot]

Acceptance criteria, ticked here because this account cannot edit the issue body (PATCH /issues/15138 → 403).

• No babel config sets useBuiltIns; polyfill-corejs3 does entry-global for the polyfills bundle and Jest, usage-global for the sandbox — grep -rn useBuiltIns outside node_modules is empty.
• All four packages declare "core-js": "catalog:" — kolibri/core/package.json:13, packages/kolibri-jest-config/package.json:21, packages/kolibri-sandbox/package.json:35, packages/kolibri-zip/package.json:10.
• Catalog at ^3.49.0; the version literal is '3.49' in all three configs. Not 3.50.0 — minimumReleaseAge blocks it until 2026-08-12. corejs: itself is gone; it was a preset-env key.
• @babel/core, @babel/preset-env, @babel/plugin-transform-runtime, @babel/runtime all ^8.0.0. The lone 7.x literal is the @babel/parser override scoped to recast.
• polyfillLoader.js comment names the feature and calls the threshold a legacy-cohort cutoff. The separation the criterion asks for is unachievable at any core-js version — measured in Upgrade to Babel 8 and unify core-js on the pnpm catalog #15138 (comment).
• core-js-compat diff 3.31 → 3.49 accounted for in the PR body: 300 → 327, 65 added, 38 removed, every removal an esnext.X with a matching es.X.
• pnpm test-jest 318/318, pnpm sandbox-build, make assets, make dist, prek — all pass locally; CI 55 green, 0 failing.
• BrowserStack Chrome 49 — not run. No credentials or tunnel in this environment. The emitted set is 327 modules and the loader's feature test is unchanged, so Chrome 49 still fires it, but that is inference, not a browser run.

[rtibbles]

Changes make sense - manual QA checks out, no regressions when testing on Chrome 65.