Add configuration defaults for nextercism

[kytrinyx]

We will be moving to a tree-shaped track rather than a linear one, as described in the progression & learning in Exercism design document.

In order to support this, we need to expand the metadata that exercises are configured with.

Note that 'core' exercises are never unlocked by any other exercises. Core exercises appear in the track in the order that they are listed in the array.

Non-core exercises depend on only one exercise (unlocked_by: ). At the moment we are assuming that this is a core exercise, but there is no reason that it needs to be.

active: false is the equivalent of deprecated, which was stored in a separate array. This array is being removed in this change.

With these defaults the track in nextercism will have no core exercises, and all the exercises will be available as 'extras' from the start.

See exercism/meta#16

[petertseng]

Planning to squash those commits.

Thinking about whether to move the deprecated into their original position from before they were deprecated, but I think I decided probably not, too hard to tell them apart if they stay in their original position?

[kytrinyx]

I think it probably doesn't matter about where the deprecated ones are in the list. I've been debating with myself which I prefer, and I can make the argument for both:

• original location: if we deprecate other exercises, they will likely stay in the original location, so putting them at the end now will cause inconsistencies later, unless we move all the deprecated ones to the end.
• at the end: it seems to keep them out of the way

[petertseng]

At exercism/discussions#159 (comment) I am discussing whether certain keys (definitely difficulty and topics, and perhaps core and depends_on) can be removed for the inactive exercises.

[petertseng]

$ cat cmp.rb

require 'json'

a = JSON.parse(IO.read(ARGV[0]))
b = JSON.parse(IO.read(ARGV[1]))

a['exercises'].zip(b['exercises']) { |ae, be|
  expected_keys = ae.keys
  expected_keys.insert(1, 'unlocked_by')
  expected_keys.insert(1, 'core')
  expected_keys.unshift('uuid')
  raise "No. #{ae['slug']} #{ae.keys} should have become #{expected_keys} but became #{be.keys} instead" if be.keys != expected_keys
}

b['exercises'].drop(a['exercises'].size).zip(a['deprecated']) { |be, deprecated|
  raise "deprecated #{deprecated} != #{be['slug']}" if be['slug'] != deprecated
}

$ ruby cmp.rb <(git show master:config.json) config.json
$