fix: generate compiler per component to pass information about scopeId

[przemkow]

Fixes #321

Changes proposed in this pull request:

• Generate compiler instance per component so component scopeId can be passed as a variable to generate correctly optimised SSR code.

I tried to add tests for that but it seems that currently tests enviroment supports only iife build.

/ping @znck

[znck]

It looks good but I need some time to properly review the code (😞 as CI is broken).

[przemkow]

yea I noticed that. No worries @znck, take you time :) if you notice that something needs to be changed let me know :)

[hjkcai]

How is it going here? I have the same problem and I really need this fix. Thanks @znck @przemkow

BTW in the fix code, is it fine to create the compiler multiple times? I am not sure about it. My fix might be simpler:

if (descriptor.template) {
  const hasScoped = descriptor.styles.some(s => !!s.scoped);

  // magic!
  Object.assign(compiler.template.compilerOptions, { scopeId: hasScoped ? scopeId : undefined });

  // ...
}

[przemkow]

@hjkcai Thanks for that suggestion! To be honest I was thinking about something similar but I wasn't sure if mutating the compilerOptions will not create any side-effects.
I noticed that vue-loader seems to create a separate instance of templateLoader per file so I tried to implement a similar approach with as small modifications as possible.
If you have some time @znck let us know what do you think about that :) If any modifications are required I will try to update this PR as soon as possible.

[znck]

Transform function is async and mutation could potentially produce wrong results.

P.S. I’ll merge it today. Apologies for the delay.

[hjkcai]

Good job @znck @przemkow

Thanks a lot