sort_nodes! changes method privacy

[mwudka]

I think that the SortNodes rewriter doesn't preserve the position of private and protected, causing it to change the privacy of methods. For example, I would expect this input:

rbi = RBI::Tree.new
rbi << RBI::Method.new("c")
rbi << RBI::Private.new
rbi << RBI::Method.new("a")
rbi << RBI::Protected.new
rbi << RBI::Method.new("b")
rbi.sort_nodes!
puts rbi.string

to produce

def c; end
private
def a; end
protected
def b; end

but it sorts everything and produces

def a; end
def b; end
def c; end
private
protected

So that method b which should be private has become public, and c which should be protected is also public.

If my understanding is correct, the problem is in the node.nodes.sort! call in the SortNodes visitor, which currently sorts all the nodes. I think it needs to first segment the nodes into public, private, and protected ranges and sort those ranges individually. Would a PR to fix this be helpful?