copy getOptions from webpack

[qnighy]

This PR contains a:

• bugfix
• new feature
• code refactor
• test update
• typo fix
• metadata update

Motivation / Use-Case

Attempt to fix #106, a major compatibility problem with Webpack 5.

Breaking Changes

No.

Additional Info

Ideally we should be able to delegate computation to the main process, but unfortunately getOptions needs to return a value synchronously. In this PR I just copied the code verbatim. Copyright-wise, it should be sufficient to ask @alexander-akait and @sokra because they seem to be the only authors of the code.

[codecov]

Codecov Report

Merging #113 (5b1945e) into master (78920d9) will decrease coverage by 0.81%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #113      +/-   ##
==========================================
- Coverage   21.84%   21.03%   -0.82%     
==========================================
  Files           8        8              
  Lines         467      485      +18     
  Branches       89       94       +5     
==========================================
  Hits          102      102              
- Misses        322      335      +13     
- Partials       43       48       +5     

Impacted Files	Coverage Δ
src/worker.js	0.00% <0.00%> (ø)

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[alexander-akait]

Ideally we should run webpack api here not copy this, because it can be bad for future webpack changes

[qnighy]

Ideally we should run webpack api here not copy this, because it can be bad for future webpack changes

I agree, though as of 5.31.2 it's hard to call webpack's getOptions from workers because it's created in NormalModule.prototype.createLoaderContext.

Possible options:

• Keep the status quo in this PR.
• Expose getOptions implementation from webpack.
• Port webpack's getOptions back to schema-utils or loader-utils or something, and use it from both webpack and thread-loader.

[qnighy]

@alexander-akait here's another attempt: webpack/schema-utils#123. Which do you think is better?

[sokra]

Seems fine to copy the implementation. I don't think we will change that in webpack any time soon (it would be a breaking change anyway).