This needs rebasing now.

That said, it never occurred to me that depth could be used as a configuration for pretty printing purposes. But if it works, why not.

Testing old versions, seems like this never really worked?

gem "json", "2.2.0"
require 'json'

puts "JSON::VERSION: #{JSON::VERSION}"
puts JSON.generate({ foo: 1 }, object_nl: "\n", array_nl: "\n", space: " ", indent: "  ", depth: 4)

$ ruby /tmp/test.rb
JSON::VERSION: 2.2.0
{
          "foo": 1
        }

Testing old versions, seems like this never really worked?

I'm not sure what you mean, your example shows that JSON.generate always respected depth?

your example shows that JSON.generate always respected depth?

Look at the opening braces. It's not respecting the depth. But the rest yes.

The opening brace being on the first character is expected, because the enclosing code should be already indenting that part. For example, to go from a fragment with depth 1 to an Array:

puts "[\n  #{JSON.generate({ foo: 1 }, object_nl: "\n", array_nl: "\n", space: " ", indent: "  ", depth: 1)}\n]"

[
  {
    "foo": 1
  }
]

Ah right, that makes sense.

Another example, using the generator to do the Array part instead of String interpolation:

gem "json", ARGV.first
require 'json'

puts "JSON::VERSION: #{JSON::VERSION}"

cache_miss = 0
cache = Hash.new do |h, k|
  cache_miss += 1
  h[k] = Fragment.new(JSON.pretty_generate({ foo: k }, depth: 1))
end

class Fragment
  def initialize(fragment)
    @fragment = fragment
  end

  def to_json(*)
    @fragment
  end
end

puts JSON.pretty_generate((1..3).map(&cache))
puts "miss:#{cache_miss}"
cache_miss = 0
puts JSON.pretty_generate((1..3).map(&cache))
puts "miss:#{cache_miss}"

This works all the way to ruby 2.7 for example:

$ cat test.rb | container run --rm -i ruby:2.7 ruby
JSON::VERSION: 2.3.0             
[
  {
    "foo": 1
  },
  {
    "foo": 2
  },
  {
    "foo": 3
  }
]
miss:3
[
  {
    "foo": 1
  },
  {
    "foo": 2
  },
  {
    "foo": 3
  }
]
miss:0