Do not stop booting if apps path is unavailable (#1812)

lib/livebook.ex

@@ -152,7 +152,7 @@ defmodule Livebook do
       config :livebook, :data_path, data_path
     end
 
-    if apps_path = Livebook.Config.readable_dir!("LIVEBOOK_APPS_PATH") do
+    if apps_path = System.get_env("LIVEBOOK_APPS_PATH") do
       config :livebook, :apps_path, apps_path
     end
 

lib/livebook/apps.ex

@@ -107,6 +107,10 @@ defmodule Livebook.Apps do
     pattern = Path.join([path, "**", "*.livemd"])
     paths = Path.wildcard(pattern)
 
+    if paths == [] do
+      Logger.warning("No .livemd files were found for deployment at #{path}")
+    end
+
     for path <- paths do
       markdown = File.read!(path)
       {notebook, warnings} = Livebook.LiveMarkdown.notebook_from_livemd(markdown)

lib/livebook/config.ex

@@ -262,33 +262,6 @@ defmodule Livebook.Config do
     end
   end
 
-  @doc """
-  Parses and validates dir from env.
-  """
-  def readable_dir!(env) do
-    if dir = System.get_env(env) do
-      readable_dir!(env, dir)
-    end
-  end
-
-  @doc """
-  Validates `dir` within context.
-  """
-  def readable_dir!(context, dir) do
-    if readable_dir?(dir) do
-      Path.expand(dir)
-    else
-      abort!("expected #{context} to be a readable directory: #{dir}")
-    end
-  end
-
-  defp readable_dir?(path) do
-    case File.stat(path) do
-      {:ok, %{type: :directory, access: access}} when access in [:read_write, :read] -> true
-      _ -> false
-    end
-  end
-
   @doc """
   Parses and validates the secret from env.
   """