Add autocorrect for unless with else check

This autocorrects an unless with else check so that we're changing it to
an `if` statement.

Author: devonremote

lib/credo/check/refactor/unless_with_else.ex

@@ -71,4 +71,23 @@ defmodule Credo.Check.Refactor.UnlessWithElse do
       line_no: line_no
     )
   end
+
+  def autocorrect(file, _issue) do
+    {:ok, quoted} = :"Elixir.Code".string_to_quoted(file)
+
+    modified =
+      quoted
+      |> Macro.prewalk(&do_autocorrect/1)
+      |> Macro.to_string()
+      |> :"Elixir.Code".format_string!()
+      |> to_string()
+
+    "#{modified}\n"
+  end
+
+  defp do_autocorrect({:unless, meta, [clause, [do: falsy, else: truthy]]}) do
+    {:if, meta, [clause, [do: truthy, else: falsy]]}
+  end
+
+  defp do_autocorrect(ast), do: ast
 end

test/credo/check/refactor/unless_with_else_test.exs

@@ -47,4 +47,38 @@ defmodule Credo.Check.Refactor.UnlessWithElseTest do
     |> run_check(@described_check)
     |> assert_issue()
   end
+
+  describe "autocorrect/2" do
+    test "changes the unless with else to an if clause" do
+      starting = """
+      defmodule CredoSampleModule do
+        def some_function(parameter1, parameter2) do
+          unless allowed? do
+            unless other_condition? do
+              something
+            end
+          else
+            something_else
+          end
+        end
+      end
+      """
+
+      expected = """
+      defmodule CredoSampleModule do
+        def some_function(parameter1, parameter2) do
+          if allowed? do
+            something_else
+          else
+            unless other_condition? do
+              something
+            end
+          end
+        end
+      end
+      """
+
+      assert @described_check.autocorrect(starting, nil) == expected
+    end
+  end
 end