Merge with config when array

[markbirbeck]

This is a fix for yargs/yargs#817.

[markbirbeck]

Shouldn't the coverage test just check the entire branch, rather than individual steps? I'm assuming that the coverage number appears to fall because I add my test in one commit before I add the code that passes that test in the next. This makes it easier to review.

[bcoe]

@markbirbeck thanks for the contribution (regarding coverage, this is a change in how coveralls works will not block the merging of this pull request).

[markbirbeck]

Thanks for the update @bcoe.

[maxrimue]

Looks great 👍

[bcoe]

@markbirbeck sorry to drop this on the floor for so long -- just working through a large backlog of issues now; having slept on this one. It comes to mind that we might want to make this a parser option that can be enabled or disabled. Here's a scenario I frequently run into:

• I'm configuring a cluster of servers, which are represented by an array; ['staging-www-1, 'staging-www-2] -- I might have this stored in a config.json.
• In production, I might wish to override this value with ['prod-www-1', 'prod-www-2'] -- with this new logic we'd instead end up with ['staging-www-1', 'staging-www-2', 'prod-www-1', 'prod-www-2']?

Perhaps we simply add a new config option, combine-arrays, which defaults to false; if turned on it would combine merge arrays:

• if multiple arrays are given as arguments: --arr 1 2 --arr 3 4.
• or if a config file is provided along with an argument.

[bcoe]

@markbirbeck does my last comment make sense? still interested in landing this?