Inherit getLocalIdent from parent loader

[odensc]

What kind of change does this PR introduce?
Bug fix.

Did you add tests for your changes?
No. (I couldn't figure out how to compose from a css file with the test helpers)

Summary
Someone using one of my libraries ran into an issue where getLocalIdent was not being applied to composed classes. (odensc/css-loader-minify-class#1)

Looking into the source code for css-loader, I found that the loader query is stringified sometimes - which causes it to lose the function reference to getLocalIdent. This PR fixes that by inheriting the getLocalIdent function from the parent loader if possible.

Also fixes #524 which was reported on this repo.

Does this PR introduce a breaking change?
No.

[jsf-clabot]

All committers have signed the CLA.

[odensc]

(not sure what's wrong with AppVeyor)

[codecov]

Codecov Report

Merging #583 into master will decrease coverage by 1.31%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##           master     #583      +/-   ##
==========================================
- Coverage   98.63%   97.31%   -1.32%     
==========================================
  Files          10       10              
  Lines         367      373       +6     
  Branches       87       89       +2     
==========================================
+ Hits          362      363       +1     
- Misses          5       10       +5

Impacted Files	Coverage Δ
lib/loader.js	93.97% <16.66%> (-6.03%)	⬇️

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[codecov]

Codecov Report

Merging #583 into master will decrease coverage by 1.31%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##           master     #583      +/-   ##
==========================================
- Coverage   98.63%   97.31%   -1.32%     
==========================================
  Files          10       10              
  Lines         367      373       +6     
  Branches       87       89       +2     
==========================================
+ Hits          362      363       +1     
- Misses          5       10       +5

Impacted Files	Coverage Δ
lib/loader.js	93.97% <16.66%> (-6.03%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update eadbd47...de2ee8f. Read the comment docs.

[michael-ciniawsky]

Could you try with

webpack.config.js

{
  loader: 'css-loader'
  options: {
    ident: 'css', // <= this line, which value isn't important
    getLocalIdent: () => {}
  }
}

This should prevent losing the reference to {Function} when options get stringified. Normally webpack >= v2.2.1 should add the ident automatically per default, but since >= 2.6.0 this seems to be buggy again 😞 . I had countless issues with that in postcss-loader

In case it doesn't work this._module is a deprecated Loader API ⚠️ , so the current fix won't work this way

[odensc]

The `ident` option does indeed work! I didn't try it because I saw it was fixed (guess not anymore). Also good to know that `_module` is deprecated. :)