Linaria not using custom babel config with rootMode: 'upward'

[rgoldfinger-quizlet]

Environment

• Linaria version: 3.0.0-beta.13
• Bundler (+ version): Webpack 5.51.2
• Node.js version: 16.8.0
• OS: macOS Big Sur 11.6

// project root
.babel.config.js
/build/webpack.config.js

// webpack.config.js
{
  test: /\.[jt]sx?$/,
  use: [
    babelLoader,
    {
      loader: '@linaria/webpack-loader',
      options: {
        babelOptions: {
          rootMode: 'upward',
        },
      },
    },
  ],
},

Description

I noticed that Linaria's Babel was not using our Babel config, even though we are using even `rootMode: 'upward' at the suggestion of https://github.com/callstack/linaria/issues/334#issuecomment-469725071.

This is because Linaria passes configFile: false to Babel when running the Babel transform: https://github.com/callstack/linaria/blob/master/packages/babel/src/transform.ts#L180

As a result, Babel will not use the root Babel config because of configFile: false. See https://github.com/babel/babel/blob/main/packages/babel-core/src/config/config-chain.ts#L155-L169

When I change to configFile: true by editing Linaria locally, I can see that Babel is using the root config, and the compile works just fine. I'd be happy to make a PR that makes this change in the Webpack 4 and 5 loaders, but I'm not sure of the implications.

Reproducible Demo

Happy to provide if requested

[Anber]

Hi @rgoldfinger-quizlet

We can't use pure user's config in transform because transform does some very specific transformations. However, we can try to resolve the config and merge it but I don't sure that Babel provides a way to do it. I have to check.

[Anber]

btw, a demo will help a lot :)

[layershifter]

Babel options are loaded differently in v5 and can be completely opted out by a feature flag, #1355.

As the issue does not have a repro, closing for now. Feel free to submit a new issue if the problem still exists.