NodePattern: Add <> for matching children in any order.

[marcandre]

These can be used multiple times in the same sequence as well as
nested.

Limitations: A sequence can only contain a single ellipsis (contained
or not within a <> sequence).

Other implementation changes:

• Captures are now an array (i.e. capture0 is now captures[0])
• Temporary variables like temp1 were renamed to node1.
• Reading tokens until a delimiter was factorized into tokens_until

Example of produced code:

# Pattern: (hash <(pair (sym $_)) $...>)

(captures = Array.new(2)) && node0.is_a?(RuboCop::AST::Node) &&
node0.children.size >= 0 &&
node0.is_a?(RuboCop::AST::Node) && node0.hash_type? &&
(captures[1] = []) && node0.children[0..-1].each_with_object({}) { |child1, matched2|
  case
    when !matched2[0] && child1.is_a?(RuboCop::AST::Node) &&
child1.children.size == 1 &&
child1.is_a?(RuboCop::AST::Node) && child1.pair_type? &&
(node3 = child1.children[0]).is_a?(RuboCop::AST::Node) &&
  node3.children.size == 1 &&
  node3.is_a?(RuboCop::AST::Node) && node3.sym_type? &&
  (captures[0] = node3.children[0]; true) then matched2[0] = true
      else captures[1] << child1
    end
}.size == 1

Fixes #6841

[marcandre]

Fixed a few small things and even found a strange JRuby bug, all green now.

[bbatsov]

Fantastic work, @marcandre!

[pirj]

Please correct me if I'm mistaken, but it seems there's a minor mistake in the description:

# Pattern: (hash <(pair (:sym $_)) $...>)

should probably be:

# Pattern: (hash <(pair (sym $_)) $...>)

[marcandre]

@pirj Both are valid and should give you similar results. Using :sym will generate node.type == :sym (note: when it is at the beginning of a sequence!), while sym will generate node.sym_type? (note: in any position), and unless it is redefined by the user, sym_type? returns type == :sym :-)
HTH

[marcandre]

PS: I believe you are right though that (sym ...) is probably more usual and better than (:sym ...). I modified my description above accordingly.

[pirj]

What makes this change double as awesome is that it also works for matching arguments, not only in a hash. 💯