Correct indentation for `for` comprehensions

[michalmuskala]

Example:

for {k, v} <- keyword,
  v = process_value(v),
  into: %{}
  do: {v, k}

To be honest, I'm not sure that's the correct way to indent it, but I can't think of a different one that would make sense.

[whatyouhide]

FWIW, that's how I indent that kind of code as well. When I need do...end in the comprehension, I usually indent like this:

for {k, v} <- keyword,
    v = process_value(v),
    into: %{} do
  {v, k}
end

Just for the record, maybe not the best way to do it.

[jesenko]

I added failing indentation tests for the cases given above + for the case when for comprehension is combined with assignment, e.g.

result =
  for {k, v} <- keyword,
      v = process_value(v)
      into: %{} do
    {v, k}
  end

[tonini]

fixed by f721fb4