Add support for nested main field selectors

[aaronadamsCA]

Fixes #217.

There's some slightly repetitive code, I just wasn't sure where a common function should live, so I left the minor copy-paste.

[codecov]

Codecov Report

Merging #218 (0a2d6f4) into master (f420039) will increase coverage by 0.31%.
The diff coverage is 66.66%.

❗ Current head 0a2d6f4 differs from pull request most recent head b96b740. Consider uploading reports for the commit b96b740 to get more accurate results

@@            Coverage Diff             @@
##           master     #218      +/-   ##
==========================================
+ Coverage   67.97%   68.28%   +0.31%     
==========================================
  Files           9        9              
  Lines         306      309       +3     
  Branches       93       95       +2     
==========================================
+ Hits          208      211       +3     
  Misses         92       92              
  Partials        6        6              

Impacted Files	Coverage Δ
src/config-loader.ts	83.33% <ø> (ø)
src/filesystem.ts	73.91% <ø> (ø)
src/match-path-async.ts	69.35% <66.66%> (+1.02%)	⬆️
src/match-path-sync.ts	79.06% <66.66%> (+0.49%)	⬆️

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[jonaskello]

Altough I would prefer to keep webpack specific stuff in the webpack plugin, resolving nested mainfields in package.json cannot be done in the plugin so I guess we need to add this.

[jonaskello]

The jsdoc currently says this about the mainFields param:

@param mainFields A list of package.json field names to try when resolving module files.

@aaronadamsCA Could you update that comment to reflect the new function? Also the same comment is in the readme.

[aaronadamsCA]

Altough I would prefer to keep webpack specific stuff in the webpack plugin, resolving nested mainfields in package.json cannot be done in the plugin so I guess we need to add this.

If you prefer, I can update the downstream PR instead to just throw an error if the script reaches an array. This syntax does not appear to be in wide use anymore; it seems to relate to a proposal that never went anywhere.

The jsdoc currently says this about the mainFields param:

@param mainFields A list of package.json field names to try when resolving module files.

@aaronadamsCA Could you update that comment to reflect the new function? Also the same comment is in the readme.

Done.

[jonaskello]

I think we could have this for completeness so let's merge it and then look into the downstream PR.

[jonaskello]

Released in 4.1.0