feat: support .vue files coverage

[rndmerle]

Hi. I managed to make .vue files coverage appear in report.

The issue is the sourcemap resource path for .vue file is a crappy Webpack loaders string from vue-loader, like "cache-loader!vue-loader!file.vue?type=script,lang=ts&".
So it's needed to clean up that path before storing the coverage report.

I've been inspired by an option on karma-coverage-istanbul-reporter doing exactly this.

[bahmutov]

@rndmerle thank you, could you sign CLA please before we can accept this PR

Also, hmm, it would be nice to test this

[bahmutov]

nice, thank you @rndmerle I really appreciate this. I will merge this feature and will create another repo with Vue example

[bahmutov]

🎉 This PR is included in version 1.4.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[bahmutov]

trying to get coverage for Vue components in https://github.com/bahmutov/code-coverage-vue-example - so far the reports have the wrong path, "src/components/src/components" even if the .nyc_output/out.json seems correct

[rndmerle]

@bahmutov I'll check it out. Pathes are fine on our project.
I was thinking it would be a good idea to base the example repo on a minimal vue-cli3 project maybe ? It would be more familiar to most user I think.

[rndmerle]

Ok I got it now. The current fix of this PR is not enough to support the sourcemaps generated by vue-loader an other loaders.
On our project the pathes are all absolute and thus it was working right away (maybe because it goes through ts-loader first). But on your repo, in out.json, inputSourceMap.sources and inputSourceMap.sourceRoot contain relative pathes.

To get a final working report we need:

path: '/absolute-path/src/component.vue',
inputSourceMap: {
  sources: ['/absolute-path/src/component.vue'],
  sourceRoot: '', // or undefined
}

But vue-loader (I guess) outputs this for regular components (non-Typescript classes like ours) and functional components:

path: '/absolute-path/src/component.vue',
inputSourceMap: {
  sources: ['component.vue'], // actually it's 'cache-loader!vue-loader!component.vue?vue&type=script&lang=js&'
  sourceRoot: 'src',
}

Unless you have a better idea we'd need to clear sourceRoot and replace sources with path's value?