feat: expose webpack target via babel caller

[DylanPiercey]

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Other... Please describe:

What is the current behavior? (You can also link to an open issue here)
Currently it is not possible to determine inside of a babel.config.js file what the webpack target being bundled for is.

What is the new behavior?
Exposes the current webpack target using the babel caller api.

Does this PR introduce a breaking change?

• Yes
• No

Other information:
I'm happy to add a test if necessary. However there are not existing tests for the already injected caller data. I think it'd require a bit of effort to setup correctly since we'd probably want to write a fake plugin which just checked what the caller was.

Implements #787

[nicolo-ribaudo]

target can also be a function, but I wonder how it interacts with config caching 🤔

[DylanPiercey]

@nicolo-ribaudo hmm. I thought it was resolved to a string by the time it got to the loader. Could very well be wrong on that though. I'm pretty sure caller will error if passed a function since they serialize it for the cache key.

[nicolo-ribaudo]

I thought it was resolved to a string by the time it got to the loader.

Oh ok, I didn't know about it 👍

[DylanPiercey]

Yes it looks like it is resolved to a string since the target for the loader is actually added by a plugin here: https://github.com/webpack/webpack/blob/0d4607c68e04a659fa58499e1332c97d5376368a/lib/LoaderTargetPlugin.js#L29 which is always passed a string. In the function target example in the webpack docs they actually use this plugin inside the function (https://webpack.js.org/configuration/target/#function).

[existentialism]

@DylanPiercey thanks!

[bpinto]

Is this working? I can't get anything other than web as my target, even though it's configured to use a browserlist environment target: 'browserslist:app'.

[DylanPiercey]

@bpinto this.target in the context of a webpack loader is the normalized target, not the raw one, so it becomes web for anything that uses browserslist.

[bpinto]

@DylanPiercey Is there a way to use webpack target (raw) for babel-loader browserlistEnv option? Thank you.

I was trying the following:

  presets: [
    [
      '@babel/preset-env',
      {
        browserslistEnv: api.caller(caller => caller.target),
        corejs: '3.22',
        useBuiltIns: 'entry'
      }
    ],

[DylanPiercey]

@bpinto I think it probably could be exposed as well, but it'd need to be a new property on the caller. Currently it is not exposed.

[bpinto]

@DylanPiercey #943