feat: make it possible to merge configurations when extending other config.

[soulgalore]

Default behavoir is as before. But you can add 'merge-extends': true
to your parser configuration that will change so that configurations
will be deeply merged instead of overwritten per key.

See #1363

[bcoe]

@soulgalore thanks for the patch 👍 might be a few days before I can review.

[soulgalore]

@mleguen Thanks for taking the time to review! I've pushed an updated version, please let me know if there's something else I missed!

[mleguen]

Thank you @soulgalore.

Would you mind updating the doc too, to add en entry for the new mergeExtends() function and a word about its effects in config()?

[bcoe]

This is looking slick to me 👍

My main nit is I think we should configure this with parserConfiguration rather than introducing a new method on yargs.

[bcoe]

@soulgalore could you please try:

npm i yargs@next and let me know if it works for you use-cases?

[soulgalore]

Thank you @bcoe ! I've tested and it works great!

[soulgalore]

One thing though @bcoe - when I tested at work I run into an issue of a three step extend described here: https://phabricator.wikimedia.org/T232467
Where the new functionality doesn't work.

I'll add a new test case first thing tomorrow and verify.

[mleguen]

@bcoe @soulgalore one of the tests added by this PR breaks on master branch :-(

  559 passing (37s)
  1 failing

  1) yargs dsl tests
       config
         extends
           deep merges configs when extending when deep-merge-config=true:
     AssertionError: expected 1 to deeply equal [ 1 ]
      at Context.it (test\yargs.js:1398:25)

[soulgalore]

@mleguen Can you share some more context? It works when I tested on my local machine with a fresh checkout just now and on Travis: https://travis-ci.org/yargs/yargs/builds/581897033

[mleguen]

@soulgalore sorry, it was a problem of outdated dependencies on my side

[bcoe]

published in yargs@14.2.0 sorry for the slow cadence lately; thanks for the contribution @soulgalore, let me know if you bump into any issues.