a |> map(m) |> join() -> map_join(a, m)

CHANGELOG.md

@@ -103,6 +103,7 @@ See the moduledoc for `Styler.Style.Configs` for more.
 * `Timex.now/1` will no longer be rewritten to `DateTime.now!/1` due to Timex accepting a wider domain of "timezones" than the stdlib (#145, h/t @ivymarkwell)
 * `with`: skip nodes which (unexpectedly) do not contain a `do` body (#158, h/t @DavidB59)
 * `then(&fun/1)`: fix false positives on arithmetic `&1 + x / 1` (#164, h/t @aenglisc)
+* rewrite `a |> Enum.map(m) |> Enum.join()` to `map_join(a, m)`. we already did this for `join/2`, but missed the case for `join/1`
 
 ### Breaking Changes
 

lib/style/pipes.ex

@@ -236,12 +236,12 @@ defmodule Styler.Style.Pipes do
   defp fix_pipe(
          pipe_chain(
            lhs,
-           {{:., dm, [{_, _, [mod]}, :map]}, em, [mapper]},
-           {{:., _, [{_, _, [:Enum]} = enum, :join]}, _, [joiner]}
+           {{:., dm, [{_, _, [mod]}, :map]}, em, map_args},
+           {{:., _, [{_, _, [:Enum]} = enum, :join]}, _, join_args}
          )
        )
        when mod in @enum do
-    rhs = Style.set_line({{:., dm, [enum, :map_join]}, em, [joiner, mapper]}, dm[:line])
+    rhs = Style.set_line({{:., dm, [enum, :map_join]}, em, join_args ++ map_args}, dm[:line])
     {:|>, [line: dm[:line]], [lhs, rhs]}
   end
 

test/style/pipes_test.exs

@@ -613,7 +613,8 @@ defmodule Styler.Style.PipesTest do
 
     test "map/join" do
       for enum <- ~w(Enum Stream) do
-        assert_style("a|> #{enum}.map(b) |> Enum.join(x)", "Enum.map_join(a, x, b)")
+        assert_style("a |> #{enum}.map(mapper) |> Enum.join()", "Enum.map_join(a, mapper)")
+        assert_style("a |> #{enum}.map(mapper) |> Enum.join(joiner)", "Enum.map_join(a, joiner, mapper)")
       end
     end