robots.txt

Add default robots.txt that allows bots access to all paths.
Add mix task to generate robots.txt taht allows bots access to no paths.
Document custom emojis, MRF and static_dir
static_dir documentation includes docs for the robots.txt Mix task.

lib/mix/tasks/pleroma/robotstxt.ex

@@ -0,0 +1,32 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Mix.Tasks.Pleroma.RobotsTxt do
+  use Mix.Task
+
+  @shortdoc "Generate robots.txt"
+  @moduledoc """
+  Generates robots.txt
+
+  ## Overwrite robots.txt to disallow all
+
+      mix pleroma.robots_txt disallow_all
+
+  This will write a robots.txt that will hide all paths on your instance
+  from search engines and other robots that obey robots.txt
+
+  """
+  def run(["disallow_all"]) do
+    static_dir = Pleroma.Config.get([:instance, :static_dir], "instance/static/")
+
+    if !File.exists?(static_dir) do
+      File.mkdir_p!(static_dir)
+    end
+
+    robots_txt_path = Path.join(static_dir, "robots.txt")
+    robots_txt_content = "User-Agent: *\nDisallow: /\n"
+
+    File.write!(robots_txt_path, robots_txt_content, [:write])
+  end
+end