Avoid importing .json files

[nicolo-ribaudo]

Q	A
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

I'm starting to check what we need to do in order to migrate to native ES modules, and this is one of the problems I found: native ESM cannot import .json files by default.

This PR replaces imports to package.json files with a compile-time macro, which is replaced with the corresponding package.json entry.

• This doesn't cause problems when releasing a new version, because we compile after bumping the version in package.json.
• This has the advantage of slightly reducing the @babel/standalone size, since it doesn't need to include the full package.json contents.

[nicolo-ribaudo]

@kaicataldo Do you know if there is an eslint rule to say something like "disallow *.json imports"? I tried looking both at the core rules and at eslint-plugin-import, but I couldn't find anything.

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

To see build info of the built libraries, click here or the icon next to each commit SHA.

Latest deployment of this branch, based on commit 771d06d:

Sandbox	Source
babel-repl-custom-plugin	Configuration
babel-plugin-multi-config	Configuration

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/39683/

[existentialism]

@nicolo-ribaudo can we use https://github.com/benmosher/eslint-plugin-import/blob/master/docs/rules/extensions.md?

[nicolo-ribaudo]

That doesn't really prevent us from importing json files, it just ensures that we explicitly write the .json extension.

[existentialism]

While not foolproof, can't we use it to at least disallow importing something with the json extension ({ "json": "never" })?

[nicolo-ribaudo]

Actually, probably it's better to do the opposite: if we require the .json extension, we'll avoid accidentally importing json files.

[nicolo-ribaudo]

The new .json imports are all removed by #12583

[JLHwung]

Do we still need to support old versions since 1) we are building on latest node 2) it is a compile-time macro?

[nicolo-ribaudo]

"compile time" means also "on Node.js 6 inside babel-jest"

[JLHwung]

Oh I thought we are replacing packageJson.field on the build step.

[nicolo-ribaudo]

Yes, but we also run Babel in jest (that's the reason why we cannot use babel.config.mjs)

[JLHwung]

What do you think extract it to a dedicated plugin in yarn workspace. No need to publish now but maybe we can decide it later. Unlike the BABEL_8_BREAKING flag remover, it falls to an optimizer plugin that will stay for a long time.

[nicolo-ribaudo]

What do you think extract it to a dedicated plugin in yarn workspace. No need to publish now but maybe we can decide it later. Unlike the BABEL_8_BREAKING flag remover, it falls to an optimizer plugin that will stay for a long time.

We would still need to run Babel inside the yarn plugin to modify the code (unless we want to hack it with regexps 😕)