Change mix format to skip empty '.ex' and '.exs' files

Author: ak3nji

lib/mix/lib/mix/tasks/format.ex

@@ -561,7 +561,7 @@ defmodule Mix.Tasks.Format do
 
   defp format_file({file, formatter}, task_opts) do
     input = read_file(file)
-    output = formatter.(input)
+    output = bit_size(input) > 0 && formatter.(input) || <<>>
     check_formatted? = Keyword.get(task_opts, :check_formatted, false)
     dry_run? = Keyword.get(task_opts, :dry_run, false)
 

lib/mix/test/mix/tasks/format_test.exs

@@ -15,6 +15,16 @@ defmodule Mix.Tasks.FormatTest do
     end
   end
 
+  test "doesn't convert empty lines into line breaks", context do
+    in_tmp(context.test, fn ->
+      File.write!("a.exs", "")
+
+      Mix.Tasks.Format.run(["a.exs"])
+
+      assert File.read!("a.exs") == ""
+    end)
+  end
+
   test "formats the given files", context do
     in_tmp(context.test, fn ->
       File.write!("a.ex", """