Add import_file_if_available, closes #4878

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: José Valim

lib/iex/lib/iex/helpers.ex

@@ -533,6 +533,15 @@ defmodule IEx.Helpers do
     end
   end
 
+  @doc """
+  Similar to `import_file` but only imports it if it is available.
+  """
+  defmacro import_file_if_available(path) do
+    quote do
+      import_file(unquote(path), optional: true)
+    end
+  end
+
   @doc """
   Evaluates the contents of the file at `path` as if it were directly typed into
   the shell.

lib/iex/test/iex/helpers_test.exs

@@ -257,11 +257,11 @@ defmodule IEx.HelpersTest do
   end
 
   test "import_file when the file is missing" do
-    assert "nil" == capture_iex("import_file \"nonexistent\", optional: true")
-
     failing = capture_iex("import_file \"nonexistent\"")
     assert "** (File.Error) could not read file" <> _ = failing
     assert failing =~ "no such file or directory"
+
+    assert "nil" == capture_iex("import_file_if_available \"nonexistent\"")
   end
 
   test "import_if_available helper" do