Make Style/GuardClause a bit more lenient when the replacement would make the code more verbose

[dvandersluis]

We currently have an exception in Style/GuardClause when the suggested replacement would be too long.

def test
  if something && something_that_makes_the_guard_clause_too_long_to_fit_on_one_line
    work
  end
end

RuboCop suggests replacing this with:

def test
  unless something && something_that_makes_the_guard_clause_too_long_to_fit_on_one_line
    return
  end
  work
end

However, this makes the code more verbose (adds a line that doesn't really add any benefit) and harder to understand (since this only happens when the line is too long, it's a safe assumption that the condition is long, and flipping it with unless adds cognitive overhead).

This exception is not covered in the style guide either, so it should be "non-breaking".

My proposal here is that if the guard clause is too line but what is inside the if is trivial (a single statement, and not a nested if), it will not be registered as an offense.

---

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[dvandersluis]

This is not strictly related to my change but I noticed it could be replaced with node.inverse_keyword.

https://github.com/rubocop/rubocop-ast/blob/816dfe7f2ca4e92c7eda226a9e8b44aa9fa81e81/lib/rubocop/ast/node/if_node.rb#L61-L73

[bbatsov]

That's an improvement for sure, but overall I think that's one of those cops that need more work and have to be relaxed a bit to focus on cases where the guard clause really improves something.