[babel 8]: Does not work with babel-loader

[nicolo-ribaudo]

💻

• Would you like to work on a fix?

How are you using Babel?

babel-loader (webpack)

Current and expected behavior

It throws

misc/babel-bugs/babel-8.0.0 is 📦 1.0.0 via ⬢ v20.4.0 
➜ ./node_modules/.bin/webpack 
asset main.js 1.53 KiB [emitted] (name: main)
./src/main.ts 39 bytes [not cacheable] [built] [code generated] [1 error]

ERROR in ./src/main.ts
Module build failed (from ./node_modules/babel-loader/lib/index.js):
Error: The `version` export of @babel/core is only accessible from the CommonJS version after that the ESM version is loaded.
    at notLoadedError (/Users/nic/Documents/misc/babel-bugs/babel-8.0.0/node_modules/@babel/core/cjs-proxy.cjs:47:10)
    at Object.get (/Users/nic/Documents/misc/babel-bugs/babel-8.0.0/node_modules/@babel/core/cjs-proxy.cjs:40:25)
    at Object.<anonymous> (/Users/nic/Documents/misc/babel-bugs/babel-8.0.0/node_modules/babel-loader/lib/index.js:13:23)
    at Module._compile (node:internal/modules/cjs/loader:1233:14)
    at Module._extensions..js (node:internal/modules/cjs/loader:1287:10)
    at Module.load (node:internal/modules/cjs/loader:1091:32)
    at Module._load (node:internal/modules/cjs/loader:938:12)
    at Module.require (node:internal/modules/cjs/loader:1115:19)
    at require (node:internal/modules/helpers:119:18)
    at loadLoader (/Users/nic/Documents/misc/babel-bugs/babel-8.0.0/node_modules/loader-runner/lib/loadLoader.js:19:17)

webpack 5.88.2 compiled with 1 error in 34 ms

Environment

Babel 8.0.0-alpha.0

[nicolo-ribaudo]

The solution is to wrap the .version access in https://github.com/babel/babel-loader/blob/70f74d852d96669d806d73c65086d506d06a093a/src/index.js#L15-L20 in a try/catch and ignore the error, and to make https://github.com/babel/babel-loader/blob/70f74d852d96669d806d73c65086d506d06a093a/src/transform.js#L39 a getter.

[JLHwung]

Since babel.version is a constant string defined from PACKAGE_JSON.version, can we duplicate that to the cjs-proxy? In a user hat I can accept that babel.otherFunctions require complex loading logic so we don't want to have both CJS and ESM versions running. But that's not the story of a constant string.