Support Babel 8 alongside Babel 7

[wagenet]

Note: This PR was written by an AI agent (Claude, via Claude Code), run by @wagenet. The code and this description are the agent's work, not his.

Widens the @babel/core peer range to ^7.17.9 || ^8.0.0.

Right now "@babel/core": "^7.17.9" is a hard install failure for anyone on Babel 8, not a warning:

npm error code ERESOLVE
npm error peer @babel/core@"^7.17.9" from broccoli-babel-transpiler@8.0.2

That makes this package the blocker for Babel 8 across the Ember toolchain — emberjs/ember-cli-babel#537 is already Babel 7/8 compatible but can't be installed until this moves.

npm test and npm run test:slow are green on both: 102/102 on @babel/core@7.17.9, 102/102 on @babel/core@8.0.1 (checked on Node 22 and 24).

Why the constraint was safe to widen

The whole @babel/core surface here is transformAsync (lib/parallel-api.js, lib/worker.js) plus require('@babel/core/package.json').version for the worker pool cache key. Both are unchanged in Babel 8, and ./package.json is still exported from the package.

Babel 8 ships as ESM, but require('@babel/core') still works from CJS via require(esm) — it's available on every Node version Babel 8 itself supports (^22.18.0 || >=24.11.0).

The options this plugin injects on its own (filename, sourceFileName) are still valid root options in Babel 8. Nothing else it adds goes to Babel.

The one behavior change

Babel 8 removed the root-level moduleId, moduleIds, getModuleId and moduleRoot options; they're read from the module transform plugin now. This plugin passes user options straight through, so anyone setting them gets Unknown option: .moduleId and has to move them:

// Babel 8
esTranspiler(inputTree, {
  babel: {
    plugins: [
      ['@babel/plugin-transform-modules-amd', { moduleIds: true, getModuleId }]
    ]
  }
});

That also takes out the moduleId: true shorthand in index.js, which derives the module id from the file's relative path and then sets Babel's root-level moduleId. There's no root option left to set, and the plugin can't guess which entry in a user's plugins array is the module transform, so the shorthand is Babel 7 only. The moduleId === true test asserts that behavior on Babel 8 rather than skipping, so the limitation stays pinned. Both are documented in the README.

If you'd rather this fail early with a broccoli-level error naming the fix instead of letting Babel's message through, say so and I'll add it.

Test changes

Two mechanical things, no behavior changes to the plugin:

• Expectations are read through readExpectation(), which prefers tests/expectations/babel8/<name> when Babel 8 is installed. Three files needed a Babel 8 variant: source map key ordering plus the new ignoreList field, var foo = _exports.foo = 5 instead of two statements, and the interop helper's parameter name.
• The module ID tests put moduleIds/getModuleId/moduleId on @babel/plugin-transform-modules-amd on Babel 8 and at the root on Babel 7. Plugin order is preserved either way. The parallel variant still round-trips a _parallelBabel object, now nested inside plugin options — serialize/deserialize already handle that depth.

CI

Adds a Babel 8 - Node 22/24 job. npm run use-babel-8 installs Babel 8 over a normal npm ci tree with --no-save --no-package-lock, so package.json and the lockfile keep pinning Babel 7 and the existing jobs are untouched. npm run test:babel-8 does the same thing locally.

The main matrix stays on Node 16/18 — Babel 8 needs Node 22+, so it can't run there.

Not changed

engines stays at 16.* || >= 18. Babel 7 still works on those, and Babel 8 enforces its own floor through its engines.

🤖 Generated with Claude Code

[wagenet]

Comment written by an AI agent (Claude, via Claude Code), run by @wagenet.

Actions don't appear to be running on this repo (/actions/runs reports 0 total), so nothing will report on this PR. I ran the workflow on the fork instead to check the CI changes actually work — all 9 jobs green, including the two new Babel 8 ones:

https://github.com/wagenet/broccoli-babel-transpiler/actions/runs/31645509456

Job	Result
Node 16 / 18 × ubuntu, windows, macOS	✅ (6 jobs, unchanged)
Floating dependencies	✅
Babel 8 - Node 22	✅
Babel 8 - Node 24	✅