Weird and inconsistent ABCSize behaviour when using guard, quote and unquote

[Eiji7]

Hi, I would like to describe it as best as I can, but I'm completely lost in what have happened, so I've written a simple script with comments so maybe someone can describe what's going wrong.

Mix.install([:credo])

sources = [
  # 3.0
  # (argument + guard + body - makes sense)
  """
  def sample(id) when is_atom(id) do
    quote bind_quoted: [id: id] do
      id
    end
  end
  """,
  # 2.23606797749979
  # (extra assign decreases size ?!)
  """
  def sample(id) when is_atom(id) do
    quote bind_quoted: [id: id] do
      id = id
      id
    end
  end
  """,
  # 1.0
  # (removing guard decreases size by 2 ?!)
  """
  def sample(id) do
    quote bind_quoted: [id: id] do
      id
    end
  end
  """,
  # 1.4142135623730951
  # (with extra assign removing guard decreases size by less than one ?!)
  """
  def sample(id) do
    quote bind_quoted: [id: id] do
      id = id
      id
    end
  end
  """,
  # 3.0
  # (argument + guard + unquote - again makes sense)
  """
  def sample(id) when is_atom(id) do
    quote do
      unquote(id)
    end
  end
  """,
  # 2.23606797749979
  # (again why the extra assign is decreasing size?)
  """
  def sample(id) when is_atom(id) do
    quote do
      id = unquote(id)
      id
    end
  end
  """,
  # 2.0
  # (in this case removing guard decreases size by 1 - makes sense)
  """
  def sample(id) do
    quote do
      unquote(id)
    end
  end
  """,
  # 2.23606797749979
  # (makes sense standalone, but in context why without guard it's increasing size now?)
  """
  def sample(id) do
    quote do
      id = unquote(id)
      id
    end
  end
  """
]

for source <- sources,
    {:ok, ast} = Credo.Code.ast(source),
    size = Credo.Check.Refactor.ABCSize.abc_size_for(ast, []) do
  IO.inspect({size, source})
end

In a real code just adding an extra variable assignment could add many points I figured out that just because of this false positive I can reduce size from 39 to 32 by … adding more code (variable assignment for each bind quoted variable)?

The more macros and the bigger quote do … end block you have the more problematic this rule is. Sometimes it's easier to just ignore the warning than changing the code. Yeah, I understand it's not designed for Elixir language, but it's not a matter of it, but a false positive it gives as without them it's really a good hint for me.

Anyway, hope it helps.