a mix task to help figure out why elixir is recompiling every file

analyze_compile.ex

defmodule Mix.Tasks.AnalyzeCompile do
  use Mix.Task

  @shortdoc "Looks for problems in compile graph"

  @moduledoc """
    This is where we would put any long form documentation or doctests.
  """

  def run(_args) do
    graph =
      File.read!("xref_graph.dot")
      |> String.trim
      |> String.splitter("\n")
      |> Enum.reduce(%{}, fn line, graph ->
        line
        |> String.split("\"")
        |> case do
          ["  ", file, _] ->
            case graph[file] do
              nil -> Map.put(graph, file, [])
              _list -> graph
            end
          ["  ", file, " -> ", depends_on, _] ->
            add_to_graph(graph, depends_on, file, false)
          ["  ", file, " -> ", depends_on, " [label=", "(compile)", "]"] ->
            add_to_graph(graph, depends_on, file, true)
          _ -> graph
        end
      end)

    # worst offenders
    graph
    |> Enum.map(fn {file, deps} ->
      {file, all_deps(graph, deps) |> Enum.uniq}
    end)
    |> Enum.sort_by(fn {_file, list} -> length(list) end)
    |> Enum.reverse
    |> Enum.take(100)
    |> Enum.each(fn {file, list} ->
      IO.puts("#{length(list) + 1}: #{file}")
    end)

    # find cycles
    graph
    |> Enum.map(fn {file, deps} ->
      {file, find_cycle(graph, deps)}
    end)
    |> Enum.find(fn
      {_file, []} -> false
      {file, list} -> IO.puts("#{file}: #{Poison.encode! list, pretty: true}")
      # {file, list} -> IO.puts("#{file}: #{Kernel.inspect list}")
    end)

  end

  defp add_to_graph(graph, file, depends_on, compile) do
    case graph[file] do
      nil ->
        Map.put(graph, file, [%{
          compile: compile,
          file: depends_on,
        }])
      list ->
        Map.put(graph, file, list ++ [%{
          compile: compile,
          file: depends_on,
        }])
    end
  end

  def all_deps(graph, deps, acc \\ [], compile_in_tree \\ false)
  def all_deps(_graph, [], acc, _), do: acc
  def all_deps(graph, [%{file: file, compile: compile} | rest], acc, compile_in_tree) do
    if Enum.member?(acc, file)  do
      acc
    else
      track = compile_in_tree || compile
      # if track do
        all_deps(graph, rest, acc ++ [file], track) ++ all_deps(graph, graph[file], acc ++ [file], track)
      # else
      #   acc
      # end
    end
  end

  def find_cycle(graph, deps, breadcrumb \\ [], compile_in_tree \\ false) do
    Enum.find_value(deps, fn %{file: file, compile: compile} ->
      track = compile || compile_in_tree
      if Enum.member?(breadcrumb, file) do
        if track do
          breadcrumb
        else
          []
        end
      else
        find_cycle(graph, graph[file], breadcrumb ++ [file], track)
      end
    end) || []
  end

end