Add new Style/CombinableLoops cop

[fatkodima]

This cop checks for places where multiple consecutive loops over the same data can be combined into a single loop.
It is very likely that combining them will make the code more efficient and more concise.

  # bad
  def method
    items.each do |item|
      do_something(item)
    end

    items.each do |item|
      do_something_else(item)
    end
  end

  # good
  def method
    items.each do |item|
      do_something(item)
      do_something_else(item)
    end
  end

Inspired by https://rules.sonarsource.com/java/RSPEC-3047

I ran it on ~30k files and it detected 133 offenses. So seems useful.

[marcandre]

Interesting. You didn't want to raise on offense for combinable each with each_with_index?

[marcandre]

I love it when you find things in this codebase 👍

[fatkodima]

Updated with suggestions.

[marcandre]

the || method_name.match?(/_each$/) is still not covered by the specs, right?

[fatkodima]

Added test for reverse_each

[marcandre]

LGTM. I'm usggesting a small wording change, and maybe @bbatsov has a better idea for the cop's name?

[bbatsov]

I'm guessing we should make this work with for as well, right? As for the name - I can't really think of a better name right now. I'm thinking, however, it'd be nice to have a similar check for conditionals - e.g. consecutive ifs with the same condition.

[fatkodima]

I'm guessing we should make this work with for as well, right?

Yes, added support for it.

I'm thinking, however, it'd be nice to have a similar check for conditionals - e.g. consecutive ifs with the same condition.

I guess it will be better implemented as a new cop?

[bbatsov]

I guess it will be better implemented as a new cop?

Yeah, definitely.