feat(webpack): allow function entries for `build.transpile`

[Atinux]

Types of changes

• Bug fix (a non-breaking change which fixes an issue)
• New feature (a non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Description

It's mostly a feature for module, thinking of @nuxt/http for example that need to add ky in build.transpile but only for legacy mode.

Before:

{
  build: {
    transpile: ['ky']
  }
}

After:

{
  build: {
    transpile: [
      ({ isModern }) => isModern ? null : 'ky'
    ]
  }
}

The main issue I see is that module author will have to check Nuxt version to be able to push a function in build.transpile otherwise it justs breaks 😢

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly. (PR: nuxt/docs#1472)
• I have added tests to cover my changes (if not applicable, please state why)
• All new and existing tests are passing.

[pi0]

The main issue I see is that module author will have to check Nuxt version to be able to push a function in build.transpile otherwise it justs breaks cry

This is a feat/fix by next release. Nothing will be breaking.

---

Some other enhancements we could do is adding an option like transpileLegacy or allow object form like { name: 'ky', legacy: true } or { name: 'ky', modern: false }

[codecov-io]

Codecov Report

Merging #6120 into dev will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##              dev    #6120      +/-   ##
==========================================
+ Coverage   95.75%   95.75%   +<.01%     
==========================================
  Files          80       80              
  Lines        2659     2665       +6     
  Branches      682      686       +4     
==========================================
+ Hits         2546     2552       +6     
  Misses         97       97              
  Partials       16       16

Flag	Coverage Δ
#e2e	100% <ø> (ø)	⬆️
#fixtures	50.91% <75%> (+0.03%)	⬆️
#unit	92.45% <100%> (+0.01%)	⬆️

Impacted Files	Coverage Δ
packages/webpack/src/config/base.js	94.89% <100%> (+0.16%)	⬆️
packages/webpack/src/config/server.js	100% <100%> (ø)	⬆️

---

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[clarkdo]

If function is one of array items, then it can only return string or regex pattern.

Do you think is there any use case for multiple functions, maybe modules ?

How about just making transpile as function, like:

transpile: () => {
  return [
    'vue-test',
    '@vue/test'
  ]
}

[clarkdo]

Should this be string ?

[Atinux]

Yes, Will update to check typeof pattern === 'string'

[Atinux]

@clarkdo Making build.transpile a function will be harder for modules author to extend it I guess, this is why I thought about handling a push as a method (see nuxt/http@2ce08de#diff-d1234a869b3d648ebfcdce5a76747d71R100)

[Atinux]

Ready to review

[manniL]

Looks like we have a duplicate code block here (as in src/config/base.js, L61-70). Could we extract it somehow?

[clarkdo]

I will do it in another pr since this has been a long time