Properly format :in composite types, closes #4672

Author: josevalim

lib/ecto/type.ex

@@ -106,7 +106,7 @@ defmodule Ecto.Type do
   >
   > When you `use Ecto.Type`, it will set `@behaviour Ecto.Type` and define
   > default, overridable implementations for `c:embed_as/1` and `c:equal?/2`.
-  > You must implement your own `c:embed_as/1` function if you want 
+  > You must implement your own `c:embed_as/1` function if you want
   > your `c:dump/1` to be called when exporting from Ecto.
 
   ## Custom types and primary keys
@@ -1408,7 +1408,7 @@ defmodule Ecto.Type do
     end
   end
 
-  def format({composite, type}) when composite in [:array, :map] do
+  def format({composite, type}) when composite in [:array, :map, :in] do
     "{#{inspect(composite)}, #{format(type)}}"
   end
 

test/ecto/type_test.exs

@@ -1433,19 +1433,18 @@ defmodule Ecto.TypeTest do
       assert Ecto.Type.format({:array, with_format_defined}) ==
                "{:array, #CustomParameterizedTypeWithFormat<:custom>}"
 
-      assert Ecto.Type.format({:array, without_format_defined}) ==
-               "{:array, #Ecto.TypeTest.CustomParameterizedTypeWithoutFormat<%{}>}"
+      assert Ecto.Type.format({:in, without_format_defined}) ==
+               "{:in, #Ecto.TypeTest.CustomParameterizedTypeWithoutFormat<%{}>}"
     end
 
     test "non parameterized type" do
-      # fallback to `inspect(type)`
       assert Ecto.Type.format(:id) == ":id"
     end
 
     test "composite non parameterized type" do
-      # fallback to `inspect(type)`
       assert Ecto.Type.format({:array, :id}) == "{:array, :id}"
       assert Ecto.Type.format({:array, {:map, :integer}}) == "{:array, {:map, :integer}}"
+      assert Ecto.Type.format({:in, :binary}) == "{:in, :binary}"
     end
   end