Don't call formatter on directories (#12488)

Author: edennis

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

@@ -551,7 +551,9 @@ defmodule Mix.Tasks.Format do
   end
 
   defp stdin_or_wildcard("-"), do: [:stdin]
-  defp stdin_or_wildcard(path), do: path |> Path.expand() |> Path.wildcard(match_dot: true)
+
+  defp stdin_or_wildcard(path),
+    do: path |> Path.expand() |> Path.wildcard(match_dot: true) |> Enum.filter(&File.regular?/1)
 
   defp elixir_format(content, formatter_opts) do
     case Code.format_string!(content, formatter_opts) do

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

@@ -81,6 +81,16 @@ defmodule Mix.Tasks.FormatTest do
     end)
   end
 
+  test "does not try to format a directory that matches a given pattern", context do
+    in_tmp(context.test, fn ->
+      File.mkdir_p!("a.ex")
+
+      assert_raise Mix.Error, ~r"Could not find a file to format", fn ->
+        Mix.Tasks.Format.run(["*.ex"])
+      end
+    end)
+  end
+
   test "reads file from stdin and prints to stdout", context do
     in_tmp(context.test, fn ->
       File.write!("a.ex", """