Allow custom directory in Migrator.migrations_path

lib/ecto/migrator.ex

@@ -161,13 +161,17 @@ defmodule Ecto.Migrator do
 
   @doc """
   Gets the migrations path from a repository.
+
+  This function accepts an optional second parameter to customize the
+  migrations directory. This can be used to specify a custom migrations
+  path.
   """
-  @spec migrations_path(Ecto.Repo.t) :: String.t
-  def migrations_path(repo) do
+  @spec migrations_path(Ecto.Repo.t, String.t) :: String.t
+  def migrations_path(repo, directory \\ "migrations") do
     config = repo.config()
     priv = config[:priv] || "priv/#{repo |> Module.split |> List.last |> Macro.underscore}"
     app = Keyword.fetch!(config, :otp_app)
-    Application.app_dir(app, Path.join(priv, "migrations"))
+    Application.app_dir(app, Path.join(priv, directory))
   end
 
   @doc """

test/ecto/migrator_test.exs

@@ -698,6 +698,20 @@ defmodule Ecto.MigratorTest do
     end
   end
 
+  describe "migrations_path" do
+    test "is inferred from the repository name" do
+      path = migrations_path(TestRepo)
+      expected = "priv/test_repo/migrations"
+      assert path == Application.app_dir(TestRepo.config()[:otp_app], expected)
+    end
+
+    test "uses custom directory when provided" do
+      path = migrations_path(TestRepo, "custom")
+      expected = "priv/test_repo/custom"
+      assert path == Application.app_dir(TestRepo.config()[:otp_app], expected)
+    end
+  end
+
   describe "with_repo" do
     defmodule Repo do
       def start_link(opts) do