Rename Dealias to AliasEnv, now that elixir 1.17 gave me much better words for everything

Author: novaugust

lib/alias_env.ex

@@ -0,0 +1,57 @@
+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, {:alias, m, [{:__aliases__, m_, modules} | rest]}),
+    do: {:alias, m, [{:__aliases__, m_, do_expand(env, modules)} | rest]}
+
+  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

lib/dealias.ex

@@ -88,7 +88,7 @@ defmodule Styler.Style.ModuleDirectives do
   """
   @behaviour Styler.Style
 
-  alias Styler.Dealias
+  alias Styler.AliasEnv
   alias Styler.Style
   alias Styler.Zipper
 
@@ -235,7 +235,7 @@ defmodule Styler.Style.ModuleDirectives do
       |> Enum.reduce(@acc, fn
         {:@, _, [{attr_directive, _, _}]} = ast, acc when attr_directive in @attr_directives ->
           # attr_directives are moved above aliases, so we need to dealias them
-          {ast, acc} = acc.dealiases |> Dealias.apply(ast) |> lift_module_attrs(acc)
+          {ast, acc} = acc.dealiases |> AliasEnv.expand(ast) |> lift_module_attrs(acc)
           %{acc | attr_directive => [ast | acc[attr_directive]]}
 
         {:@, _, [{attr, _, _}]} = ast, acc ->
@@ -245,8 +245,8 @@ defmodule Styler.Style.ModuleDirectives do
           {ast, acc} = lift_module_attrs(ast, acc)
           ast = expand(ast)
           # import and used get hoisted above aliases, so need to dealias
-          ast = if directive in ~w(import use)a, do: Dealias.apply(acc.dealiases, ast), else: ast
-          dealiases = if directive == :alias, do: Dealias.put(acc.dealiases, ast), else: acc.dealiases
+          ast = if directive in ~w(import use)a, do: AliasEnv.expand(acc.dealiases, ast), else: ast
+          dealiases = if directive == :alias, do: AliasEnv.define(acc.dealiases, ast), else: acc.dealiases
 
           # the reverse accounts for `expand` putting things in reading order, whereas we're accumulating in reverse
           %{acc | directive => Enum.reverse(ast, acc[directive]), dealiases: dealiases}
@@ -327,7 +327,7 @@ defmodule Styler.Style.ModuleDirectives do
   defp lift_aliases(%{alias: aliases, require: requires, nondirectives: nondirectives} = acc) do
     # we can't use the dealias map built into state as that's what things look like before sorting
     # now that we've sorted, it could be different!
-    dealiases = Dealias.new(aliases)
+    dealiases = AliasEnv.define(aliases)
     excluded = dealiases |> Map.keys() |> Enum.into(Styler.Config.get(:lifting_excludes))
     liftable = find_liftable_aliases(requires ++ nondirectives, excluded)
 
@@ -339,7 +339,7 @@ defmodule Styler.Style.ModuleDirectives do
 
       aliases =
         liftable
-        |> Enum.map(&Dealias.apply(dealiases, {:alias, m, [{:__aliases__, [{:last, m} | m], &1}]}))
+        |> Enum.map(&AliasEnv.expand(dealiases, {:alias, m, [{:__aliases__, [{:last, m} | m], &1}]}))
         |> Enum.concat(aliases)
         |> sort()