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A code-style enforcer that will just FIFY instead of complaining

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styler lib alias_env.ex
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lib/alias_env.ex 

defmodule Styler.AliasEnv do

  @moduledoc """

  A datastructure for maintaining something like compiler alias state when traversing AST.



  Not anywhere as correct as what the compiler gives us, but close enough for open source work.



  A alias env is a map from an alias's `as` to its resolution in a context.



  Given the ast for



      alias Foo.Bar



  we'd create the env:



      %{:Bar => [:Foo, :Bar]}

  """

  def define(env \\ %{}, ast)



  def define(env, asts) when is_list(asts), do: Enum.reduce(asts, env, &define(&2, &1))



  def define(env, {:alias, _, aliases}) do

    case aliases do

      [{:__aliases__, _, aliases}] -> define(env, aliases, List.last(aliases))

      [{:__aliases__, _, aliases}, [{_as, {:__aliases__, _, [as]}}]] -> define(env, aliases, as)

      # `alias __MODULE__` or other oddities i'm not bothering to get right

      _ -> env

    end

  end



  defp define(env, modules, as), do: Map.put(env, as, do_expand(env, modules))



  # no need to traverse ast if there are no aliases

  def expand(env, ast) when map_size(env) == 0, do: ast



  def expand(env, ast) do

    Macro.prewalk(ast, fn

      {:__aliases__, meta, modules} -> {:__aliases__, meta, do_expand(env, modules)}

      ast -> ast

    end)

  end



  # if the list of modules is itself already aliased, dealias it with the compound alias

  # given:

  #   alias Foo.Bar

  #   Bar.Baz.Bop.baz()

  #

  # lifting Bar.Baz.Bop should result in:

  #   alias Foo.Bar

  #   alias Foo.Bar.Baz.Bop

  #   Bop.baz()

  defp do_expand(env, [first | rest] = modules) do

    if dealias = env[first], do: dealias ++ rest, else: modules

  end

end