Adds backport for &build_slug/1

lib/ecto_autoslug_field/slug.ex

@@ -72,7 +72,7 @@ defmodule EctoAutoslugField.SlugBase do
 
   It should return a `binary` or `nil`.
   """
-  @spec build_slug(Keyword.t, Changeset.t) :: String.t
+  @spec build_slug(Keyword.t, Changeset.t | nil) :: String.t
   def build_slug(sources, changeset), do: SlugGenerator.build_slug(sources, changeset)
 end
 
@@ -184,9 +184,15 @@ defmodule EctoAutoslugField.Slug do
         SlugBase.get_sources(changeset, opts)
       end
 
-      def build_slug(sources, changeset), do: SlugBase.build_slug(sources, changeset)
+      def build_slug(sources) do
+        SlugBase.build_slug(sources, nil)
+      end
+
+      def build_slug(sources, _changeset) do
+        build_slug(sources)
+      end
 
-      defoverridable [get_sources: 2, build_slug: 2]
+      defoverridable [get_sources: 2, build_slug: 2, build_slug: 1]
 
     end
   end

test/ecto_autoslug_field_test/edge_cases_test/build_slug_arity_2_test.exs

@@ -0,0 +1,44 @@
+defmodule EctoAutoslugField.SlugTest.EdgeCases.Arity2 do
+  use ExUnit.Case
+
+  defmodule StringSource do
+    use EctoAutoslugField.Slug, to: :slug, from: :title
+
+    def build_slug(sources) do
+      sources
+      |> super()
+      |> String.replace("-", "*")
+    end
+  end
+
+  defmodule Article do
+    use Ecto.Schema
+    import Ecto.Changeset
+
+    schema "articles" do
+      field :title, :string
+      field :slug, StringSource.Type
+    end
+
+    def changeset(model, params \\ :invalid) do
+      model
+      |> cast(params, [:title, :slug])
+      |> validate_required([:title])
+      |> StringSource.maybe_generate_slug
+    end
+  end
+
+  setup do
+    {:ok, %{article: Article.changeset(
+      %Article{}, %{"title": "Some article title"})
+    }}
+  end
+
+  test "changeset is valid", %{article: article} do
+    assert article.valid?
+  end
+
+  test "build_slug/2 is working", %{article: article} do
+    assert article.changes.slug == "some*article*title"
+  end
+end